This chapter will cover items that are estimated in the concrete phase of construction. This will include concrete footings, foundations, floors, sidewalks, driveways, patios, stairs, and miscellaneous concrete items. The discussion will begin with footings.
Estimating concrete footings begins with estimating the formwork needed for the footings. There are a number of ways that concrete footings can be formed. Each has advantages and disadvantages. The three most common are trench footings, 2″× 10″ formed footings, and 2″× 4″ formed footings.
The most basic method of forming concrete footings is to dig a trench in the soil, place the reinforcing steel, and fill the trench with concrete. This method is usually the least expensive option for forming footings because separate form material does not have to be purchased. However, there are several disadvantages to this method. The first is that not all soils are suitable for trench footings. Soil that has a high clay content and holds its shape works well for forming trench footings. Sandy or gravelly soils, however, are not because of the difficulty in getting these soils to hold their shape after the trench is dug. The soil tends to slough off into the footings, making it difficult to pour and finish the concrete. Another drawback is the difficulty in getting level because there are no flat footing sides to screed the concrete off. With this method, metal rebar stakes are placed in the center of the trench at regular intervals, and the top of the stakes are set to the finished elevation using a transit or laser level (Figure 8-1). The top of the concrete is poured to the top of the grade stakes, which are used as a reference when floating to the top of the surface.
Another disadvantage to this method of forming is that it is more difficult to accurately estimate the amount of concrete that will be used because of the inconsistencies in the footing depth and shape. Commonly, a larger waste factor would be used when estimating trench footings.
Estimating trench footings is typically an excavation problem. The quantity to be excavated in cubic yards can be calculated by multiplying the length, depth, and thickness. Alternatively, it may be calculated as a lineal footage of trenching.
2″× 4″ Footing Forms
A second method of forming footings is to use 2″× 4″ or 2″× 6″ framing lumber to form the top of the footings and then to either backfill the open portion at the bottom of the footing, or excavate a few inches of soil at the base of the footings (Figure 8-2). The advantage of this method is that the footings can be formed more precisely, and the form tops can be used to screed the concrete, which results in a more level footing. The disadvantage is the time that is required to build the forms and the cost of the form material, although the cost of the form material is considerably less than purchasing material to form the footings at full depth.
There can be considerable hand labor involved, either backfilling around the footing forms or hand excavating the base of the footings.
Estimating 2″× 4″ footings requires calculating both the quantity of form material to be purchased and the quantity of soil to be either hand excavated or backfilled. The quantity of form side material is calculated by multiplying the length of the footings by the number of form sides (typically two). For a project with 216 lineal feet of footing, there would be approximately 432 lineal feet of forms to purchase and 216 lineal feet to excavate.
2″× 10″ Footing Forms
The third method of forming footings is to use 2″× 8″, 2″× 10″, or 2″× 12″ framing lumber to form the footings. This is the most common method used. The wider lumber allows the footings to be formed full width with very little backfill or hand excavation required (Figure 8-3).
Estimating 2″× 10″ requires calculating the quantity of form material to be purchased. The quantity of form material is calculated by multiplying the length of the footing by the number of form sides (typically two). For a project with 216 lineal feet of footing, there would be approximately 432 lineal feet of forms to purchase.
Number of Form Uses
Another aspect of the purchase of footing formwork material that needs to be part of the equation is the number of form uses. Framing lumber for form material is expensive and contractors try to reuse material when possible (Figure 8-4). Still, each time footings are formed, some of the material that was used is destroyed and cannot be reused in future formwork. This is typically accounted for by adding a number of form variables to the equation. A typical example is that a set of forms could be used in five separate footings before the material is too damaged to be used any further. With this example, the estimate for footing material for any single project would be one-fifth of the total amount needed for the project. The expectation is that the other four-fifths would be brought from old projects and reused. Using the previous estimated quantity of 432 lineal feet of formwork, only one-fifth or 87 lineal feet would be included in the estimate for that project.
Stakes and Spreaders
Footings formed by either the 2″× 4″ or the 2″× 10″ method require stakes and spreaders. The stakes are used to anchor the forms to the ground and hold them in place, and spreaders are used to keep the forms from spreading apart from the pressure of the concrete. Stakes can be made of either wood or metal. Metal stakes are typically reused time and time again and only a small amount is included in the estimate to cover the stakes that are lost or unusable after the project. Wooden stakes are typically destroyed with a project and are considered disposable. New stakes are usually purchased with each project. The number of stakes needed is dependent upon the type and size of the footing, but a common example would be to use two stakes for every four lineal feet of footing. This would place one stake on each side of the formwork every four feet. In the previous example, using 150 lineal feet of footings, the number of stakes needed would be
Wooden stakes are usually sold in bundles of 24 stakes, so three bundles would be insufficient and four bundles would need to be purchased.
Spreaders are used to keep the forms a consistent distance apart (Figure 8-5). They are usually made from some type of framing lumber, such as 1″ × 2″ × 8′ furring strips. They are usually placed approximately every four feet of footings. The quantity of spreader material is calculated by multiplying the number of spreaders by the length of each spreader and dividing by the length of the spreader material. Each spreader is usually the width of the footing plus an additional three inches to account for the thickness of the form material. Footings that are 18 inches wide would require spreaders that are a minimum of 21 inches long. Using the above example of 150 lineal feet of footings, 38 spreaders would be needed.
Each spreader would need to be at least 21 inches long. If they were cut out of 1″ × 2″ × 8′ spreader material, one board would yield four spreaders, which would require the purchase of ten boards.
Steel rebar is often placed in concrete to strengthen it. The combination of steel and concrete together make a better structure than either alone. This is because they have complimentary characteristics. Concrete is very good under compression and can carry large compressive loads, however, it is relatively weak under tension. To compensate for this weakness, steel is embedded in the concrete because steel has a high tensile strength.
Steel rebar used in construction is usually deformed rebar. This means that the rebar has been made with ribs and depressions on its surface (Figure 8-6). The deformations help the concrete to mechanically bond to the rebar surface and prevent slippage under heavy loads. Still, under very heavy loads, such as earthquakes, the rebar can pull out of the concrete. The individual pieces of rebar are tied together, or there are bends and hooks in the rebar to tie it to each other to increase bonding capacity.
Steel rebar comes in many different types and styles. The most common type is black rebar, however, it is also available in epoxy coated, zinc coated, and stainless steel for special applications. Different strength grades of rebar are also available such as grade 40 with a minimum yield strength of 40,000 pounds per square inch or grade 60 with a minimum yield strength of 60,000 pounds per square inch. Rebar is sized by diameter in units of one eighth of an inch and given designations such as #4 bar, which refers to rebar four eighths or one half of an inch in diameter. Standard rebar sizes in the United States range from #2 bar (1/4″) to #18 (2-1/4′). Rebar is also sold in standard lengths of 20 feet (most common size), 30 feet, 40 feet, and 60 feet.
In residential construction, rebar is often purchased in 20 foot lengths. Once on site, the individual pieces of rebar are cut and bent to meet the needs of the project using portable rebar forming equipment shown in Figure 8-7.
On some projects, both straight 20-foot length and prefabricated shapes may be purchased (Figure 8-8).
Two types of steel reinforcing are commonly embedded in concrete footings: horizontal rebar and vertical rebar.
Horizontal rebar is placed in the footings in one or more continuous bands that are made up of individual pieces of rebar that have been bent and tied together to mirror the path of the footings. The individual rebar pieces are overlapped before they are tied together with a code minimum overlap requirement of 24 bar diameters. This means that a #4 rebar, which has a diameter of one half an inch, would require a minimum of 12 inches of overlap where two bars are tied together. Figure 8-9 shows an example of two rows of #4 horizontal rebar bent to match the shape of the footing. Individual pieces of rebar are lapped a minimum of 12 inches and tied together.
Estimating horizontal rebar is done by multiplying the lineal feet of footing by the number of pieces of rebar. In the previous example of 150 lineal feet of footing, there would be roughly 300 lineal feet of rebar. However, additional rebar will be needed to compensate for the lapping requirement. Because #4 rebar requires a minimum of 12 inches of lapping, each 20-foot piece of rebar will yield only 19 feet of usable rebar. The formula for calculating rebar under these circumstances would be as follows:
This would be rounded up to a total of 23 pieces of rebar to meet the horizontal rebar requirement.
Vertical rebar is usually required in concrete footings that support concrete or masonry walls. The vertical rebar connects the footing and foundation together. Usually, the code minimum requirement is one #4 for rebar spaced a maximum of 48″ on-center, but local requirements may require a closer spacing or larger rebar. The vertical rebar has a hook bent on the end that anchors it into the concrete. The vertical rebar is most often placed in the footings after the concrete has been placed, but while it is still pliable (Figure 8-10). It may be placed in the footings prior to the placement of the concrete and braced and tied into place as shown in Figure 8-11. In both cases, the rebar and concrete needs to stand undisturbed until the concrete is allowed to harden.
The fabricated length of vertical rebar is determined by three factors: the hook length, the embed length, and the exposure length. Standard engineering design sets the hook length at 12 times the rebar diameter. This would mean a six-inch hook length for a standard #4 bar. The embed length is determined by the thickness of the footing and the amount of rebar embedded in the footing. Code requires the rebar to have a minimum of three inches of concrete cover between the rebar and the bottom of the footing. The maximum embed depth for an eight-inch-thick concrete footing would be five inches, but the distance could be as small as three inches. The IRC requires the footing reinforcing to extend a minimum of 14 inches into the stem wall that the footing supports. A minimum length for the vertical rebar in an eight-inch-deep by sixteen-inch-wide footing using #4 rebar would be calculated as follows:
Hook Length = 6″
Maximum Embed Depth = 5″
Minimum Exposure Length = 14″
6″ + 5″ + 14″ = 25″
This would be the minimum length for the vertical footing rebar, however, it is often made longer. One consideration for determining the length would be to size the rebar so that a standard 20-foot length would be cut into equal segments without significant leftover waste. It is not uncommon in a residential setting for the vertical rebar in the footings to have a minimum of 25-inch exposure to accommodate the vertical rebar in the foundation wall. Figure 8-12 shows an example of an 8″× 16″ footing with two pieces of horizontal rebar and vertical rebar spaced at 32 inches on-center. The exposure length of the vertical rebar is 25 inches with a five-inch embed distance and a six-inch hook length.
The length calculations for the vertical rebar length would be as follows:
Hook Length = 6″
Embed Depth = 5″
Exposure Length = 25″
6″ + 5″ + 25″ = 36″
If a 20-foot length were to be cut into 36-inch segments, each 20-foot piece would yield
20 ft. ÷ 3 ft. = 6.67 pieces
Each 20-foot length would yield six pieces with some waste. Determining the number of pieces of vertical rebar is calculated by dividing the length of the footing by the vertical rebar spacing and adding an additional piece of rebar for each footing corner and intersection. In the previous example of 150 feet of footing with a rebar spacing of 32 inches and eight corners and intersections, the number of horizontal rebar would be as follows:
216 ft. ÷ 2 ft. − 8 in.= 81 pcs.
81 pcs.+8 pcs.= 89 pcs
89 pcs. ÷ 6 pcs. = 14.8 rounded to 15 pcs. of rebar
Footing without Vertical Rebar
Some footings do not have vertical rebar even if there is horizontal rebar. Typically, these types of footings are used to support load bearing walls that are not made of masonry or concrete such as interior wood framed bearing walls. One example of load bearing footings is shown in Figure 8-13. These interior grade footings are formed and poured at the same time as the exterior wall footings. They have horizontal rebar in them, but the vertical rebar has been omitted. Later, backfill will be placed to the level off the top of the footings and a concrete floor will be poured in the basement. Wood framed walls will also be built on the concrete to support the first floor framing. Figure 8-14 shows interior grade footings in a crawl space construction. In this example, wood framed load bearing pony walls will be built directly on the footing to support the first floor framing.
Figure 8-15 shows another type of interior footing called a thickened slab footing. This type is used when a concrete floor is poured. Soil is excavated where the footing is located. Horizontal rebar is placed in the excavation, and the footing and floor are poured as a single monolithic pour.
Most concrete for residential construction projects is delivered to the job site in ready-mix concrete trucks. Several factors need to be taken into consideration when estimating the concrete including the quantity of concrete needed, the design mix of the concrete, the concrete placing method, and any curing requirements.
Calculating the Quantity of Footing Concrete
Concrete is calculated as a cubic foot quantity that is then converted into a cubic yard quantity when ordering from the ready-mix company. The footing dimensions determined when completing the basic takeoffs can be used to calculate the quantity of concrete in the footings. For example, the dimensions of the exterior wall footing given in the basic takeoffs are listed as 16 inches wide, 8 inches thick, and 216 feet long. The calculations for determining the quantity of concrete would be done by first converting the inch dimensions to feet and then multiplying the feet amounts and converting the total to cubic yards.
16″ × 8″ × 216′ = Total Cubic Feet
1.33′ × .67′ × 216′ = 192 ft3
The minimum quantity of concrete that can be ordered at most ready-mix companies is one quarter of a cubic yard. Quantities of concrete calculated should be rounded up to the next cubic yard when estimating. The total quantity of concrete ordered for this footing would be equal to 7.25 cubic yards.
Delivering concrete can be costly, and ready-mix companies like to deliver full trucks of concrete whenever possible. Concrete ready-mix trucks range in size from smaller eight cubic yard rear discharge trucks (Figure 8-16) to larger eleven cubic yard front discharge trucks (Figure 8-17). Ready-mix companies typically charge an extra fee for delivery of loads that are less than the capacity of the truck. This is known as a short-load fee. Short-load fees can add 15 to 20 dollars for each cubic yard short of a full load.
Concrete Design Mix
Concrete is primarily a mix of coarse aggregate, fine aggregate, and Portland cement, also known as gravel, sand, and cement. The exact portions of each element in the mix is one of the factors that determines the characteristics of the concrete, including its strength and durability. In addition, other chemicals or substances known as admixtures can be added to the mix to change or enhance the properties of the concrete. Batch plants (Figure 8-18) have specific recipes for these elements and can greatly affect the cost of the concrete. A discussion of these admixtures is beyond the scope of this text.
The strength of the concrete is one of the most important factors when using concrete. Concrete strength is defined by the pounds per square inch (psi) that it can support. Concrete footing strength requirements can vary from around 2,500 psi to 5,000 psi or more depending on the needs of the specific project. The strength of the concrete for a given project usually can be found in the plans or specification. There may be specific location strength requirements required by the building code or structural engineer. Concrete with higher strength requirements typically have more cement in the mix, which increases the cost of the mix. An old-fashioned method of specifying concrete strength is to identify it by the bag mix. A bag mix is the number of standard 94 lb. bags of cement in the mix per cubic yard of concrete. Bag mixes usually range from a somewhat weak 4-bag mix, which would be comparable to around a 2000 psi concrete to a 7-bag mix, which would equate to around a 5,000 psi concrete.
Concrete Placing Method
The method of placing the concrete in the footings can vary greatly and add significantly to the cost of the concrete. The concrete can be placed by direct chute, in which case the truck will need sufficient access to the job site to be able to reach all of the footings with the concrete chute (Figure 8-19). If the concrete cannot be delivered via the chute, it may need to be pumped or delivered with a crane and a bucket. Each of these options add to the cost of placing the concrete. In addition, ready-mix companies usually provide a specific time period for the unloading of the concrete truck and lengths of time greater than the allowance may result in an overcharge.
Concrete turns from its plastic state to a solid state in a chemical process known as hydration. During the hydration process, the water in the concrete forms chemical bonds with the compounds in the cement in the form of hydrates. The hydration process begins rapidly after the concrete is mixed and water is added. As the concrete continues to set, the hydration process begins to slow down but continues for some time depending upon a number of factors. The strength of specific concrete is tested by taking samples in the form of cylinders from the concrete ready-mix truck and allowing them to cure for a specific period of time. The cured cylinders are then broken and the specific psi at which the cylinder shattered is noted. Common cure times in the construction industry for curing and testing cylinders are seven days and 28 days.
The hydration process can be impacted by a number of factors including the design mix, the water in the mix, and the curing temperature. The specific design mix of the concrete determines what the concrete’s anticipated strength should be. The water in the concrete mix can affect the ultimate strength that the concrete should obtain. Too much water in the initial mix can weaken the concrete, but the reverse is also true, if the water in the mix is allowed to evaporate before it has time to combine with the cement compounds, the mix will be weaker. Once the concrete is placed, steps can be taken to slow the evaporation of the water into the atmosphere or seepage into the ground to allow sufficient time for most of the water in the concrete to hydrate with the cement. Temperature can also have an effect upon the concrete hydration process. Hot temperatures can accelerate the process but can also increase the rate of evaporation. The reverse is also true. Cold temperatures slow down the hydration process. If the water in the concrete is allowed to freeze before the concrete has reached a strength of 500 psi, the hydration process will be irreplaceably impacted and the strength of the concrete permanently impacted.
Curing is the process of using some artificial means to maintain ambient conditions so that the concrete may develop its designed strength. It may involve providing some form of barrier to slow the evaporation of water such as leaving the formwork in place for an extended period of time, covering the concrete with plastic sheathing, or applying a curing compound to the concrete surface.
Curing may also involve tenting around the concrete, providing artificial heat to keep the concrete warm, or covering recently poured concrete with thermal blankets (Figure 8-20) to allow it to retain the heat that is generated during the hydration process. Any curing needs must be accounted for when preparing an estimate.
Footing Material Costs
This section will focus on the concrete footing material. The emphasis will be on creating an assembly’s estimate from the various elements that are part of forming, placing, and stripping concrete footings. Creating assemblies is a powerful way of estimating that can greatly speed up and simplify the estimating process. With a properly structured takeoff assembly, a few simple inputs or basic takeoffs will be inputted, and a basic unit of cost, such as price per lineal foot, will be developed.
Completing the Footing Material Header Section
Figure 8-21 shows an example of the footings and formwork that will be estimated. Two types of footings are identified: the exterior wall footings and the interior grade footings. In order to create your assembly, you will need to know the following variables.
Number of Footing This Size.This variable is used to determine how many footings of a particular size and makeup there are. Most often, the input would be one for continuous strip footings even if there are several instances of the same footing type in a project.With strip footings, the important measurement is the length. The most likely instance when the variable would be higher is when it is used to identify a number of spot footings, each of which are the same size as the other. In Figure 8-22, the input has been set at one for both the exterior wall and grade beam footings.
Number of Horizontal Rebar. This variable is used to determine how many pieces of horizontal rebar there are in the footing assembly. Typical residential footings have two pieces of #4 rebar placed horizontally in the bottom of the footings, as shown in Figure 8-23; however, this number could easily be changed depending on the specific code and engineering requirements of the project.
Vertical Rebar Spacing. The vertical rebar spacing variable is used to determine the spacing for vertical rebar or dowels in the footings that will tie to the vertical rebar in the foundation. The spacing is determined by the engineering requirements of the project or the building code. Not all footings require vertical rebar. Only those footings that will have concrete foundation walls on them will need vertical rebar to tie the footing and foundation together. For our example, the vertical rebar spacing has been set to 2′-8″ for the exterior wall footings and to zero for the grade beam footings because there is no vertical rebar in that footing.
Rebar Lap Length. The rebar lap is the code required distance that two pieces of rebar must lap each other when they are being tied together. The code requirement is that rebar must lap by 24 bar diameters. A #4 rebar, such as is in this project, is one-half-inch in diameter, and therefore, the lap length requirement is 24 × 1/2″ or 12 inches, which is equal to one foot.
Vertical Rebar Length. The vertical rebar length is the length of the piece that vertical rebar is cut to before it is bent to make the footing dowels. This will include the exposed length of the rebar, the distance that is embedded into the footing, and the length of the hook. Figure 8-16 shows an example of the vertical rebar length for the footings in the example. The exposure length is 25″, the embedded length is 5″, and the hook length is 6″, for a total length of 36″. Thus the standard 20-foot length of rebar can be cut into six 36″ inch pieces with some waste.
Number of Corners or Intersections. Whenever there is vertical rebar, there is usually a piece of vertical rebar in the corner of each footing or at the intersection of two footings. This variable is a count of how many corners or intersections there are that have a piece of vertical rebar in them and will add another vertical rebar to the count. A judgement call may be necessary in determining this number. Figure 8-25 shows the vertical rebar in the footings.
Because the interior grade footing has no vertical rebar, the intersection between the interior grade footing would not be counted as an intersection where an extra rebar would be placed and would not have rebar there unless, as is the case in this instance, the rebar at the intersection falls close to the normal on-center spacing layout. The intersection between the main footing and the front porch may or may not require additional rebar. The choice would be made depending upon whether or not the on-center spacing is close to the normal on-center spacing. In this instance, the number eight is placed in the header section for this variable, based upon the number that is highlighted in red in Figure 8-25.
Number of Form Sides. This variable counts the number of sides for each form. This is used in determining the amount of form material to purchase. This number is generally two for standard strip footings but can be different. For example, a spot footing would have four sides to it, and a trench footing would have zero sides.
Form Brace Spacing. This variable determines the interval that is needed for stakes or other form bracing. Four feet is generally used for standard strip footings, but the number could be higher when the bracing needs are greater and could be lower with some types of footing forms. For example, trench footings usually have no need for bracing.
Number of Form Uses. It is common construction practice to use concrete form lumber more than one time. The forms are usually disassembled and moved to the next job. However, each time a set of forms are used, there is a certain amount of waste and new forms will need to be bought. In this example, it will be assumed that each piece of form material can be used at least five times. So for each new job, only one-fifth of the form material will be purchased for use on this job. The rest of the material will be brought from other jobs.
Once you know all of these variables, you can calculate how much of each material will be used per lineal foot of footing.
Misc. Footing Material
Miscellaneous footing materials can include bracing, form release, tie wire, and nails. Some quantities can be calculated, and some are estimated based upon past experience.
Bracing. Not all footing formwork needs bracing. Often, forms are braced by shoveling dirt up against the forms. Footings that are taller or have significant pressure may require additional bracing.
Form Release. Form release is a chemical agent that is applied to concrete formwork to aid in removing the forms after the concrete has hardened. It is typically applied as a liquid or powder to the formwork as it is installed. Calculating the amount of form release is done by determining the square footage of formwork area that is in contact with the concrete. This is typically called square footage of contact area or SFCA. Most form release manufacturers will provide product data including the recommended coverage rate in square foot per gallons. Some products have different coverage rates for different form material. For example, steel forms would require less form release material than porous plywood forms. To calculate the quantity of form release, simply divide the SFCA by the coverage rate per gallon for that product on the formwork material.
Tie Wire. Concrete tie wire is used to tie reinforcing together to form the rebar grid work together. It is commonly sold in 3-/12 pound rolls or in bundles of preformed looped pieces. One roll of wire would be sufficient for a project of this size.
Nails. Formwork is usually installed using duplex headed nails. These nails are manufactured with a double head. The nails are hammered in tight to the first head to hold the formwork tight together, however, the second head is left exposed so that hammer claws or a pry bar can be used to remove the nails when disassembling the forms. Nails are sized by a unit known as a penny, which is abbreviated with the letter d. Formwork nails are usually 8d, 12d, and 16d size, which equates to 2-1/2″, 3-1/4″, and 3-1/2″ respectively. These nails are usually purchased by the 50 lb. box, which is many more than will be used on a single residential project. Only a portion of the box will be used with the quantity in pounds estimated for this single project at five pounds of both 8d and 16d nails.
The form release material located on the concrete database is entered into the materials column along with the size, units, and unit cost. The quantity is calculated by dividing the SFCA of the total footings from the header section by 300, which is the application rate per gallon for the form release.
The concrete footing labor can be estimated using the residential section of the National Construction Estimator. There are three main costs involved in pricing footing labor: board forming and stripping, install reinforcing, and placing concrete.
Board Forming and Stripping
The first footing labor quantity to be estimated will be board forming and stripping. This is a labor cost for both forming and stripping the footings after the concrete is poured. NCE Figure 8-1 shows a screenshot of the board forming and stripping section of the NCE.
The overview clarifies that this section would be appropriate for estimating a number of concrete items including both wall and grade beam footings. It also defines the unit of measurement as per square foot of contact area and explains that for estimating footings “when the forms are required on both sides of the concrete.” That is the case in this example; the square footage of contact area for both sides of the footings should be used.
The square footage of contact area information is calculated by multiplying the length of the footings by the footing height and the number of form sides.
The price for board forming and stripping identifies the prices based upon number of uses, however, this only has application with the material cost, and the material cost has already been calculated with the footing forms cost.
NCE Figure 8-2 shows a screenshot of the NCE Concrete Reinforcing Steel section. The costs are priced both by the pound and lineal foot.
The lineal footage of footing rebar is calculated by multiplying the total lineal footage rebar purchased by multiplying the number of 20-foot lengths of rebar for both the horizontal and vertical rebar in the exterior wall footing.
The concrete footing labor is determined by using the Column Footings subsection of the NCE (NCE Figure 8-3).
The price is established per cubic yard.
You can complete both the interior grade footing materials and labor portions of an estimate using information from the basic takeoffs and details in the plans and specification.
Estimating concrete foundations begins with estimating the foundation formwork. Foundation formwork can be erected using a number of different methods. Forms can be built out of plywood and other framing lumber, or they can be set up using pre-manufactured foundation forms. In addition to the forms themselves, other concrete form material will need to be estimated including snap ties, clamps, walers, strong backs, bracing, and form release. Other elements that will become part of the finished foundation will need to be estimated as well including steel rebar, door and window bucks, block outs, and the concrete itself.
One method of forming concrete foundations is with plywood forms. The material may simply be sheets of plywood, or it may be special plyform material that has a hard, impregnated phenolic resin coating. Typically, the form material is drilled with a pattern of holes that are used for the placement of snap ties to hold the foundation forms together (Figure 8-34).
Figure 8-35 shows the formwork in a large commercial project for a concrete foundation that is over 16 feet tall. The formwork shows multi-levels of plyform material with many horizontal levels of walers, some held in place by the snap tie clamps and others held in place by the vertical strong backs. The entire assembly is braced and straightened by long 2″× 10″ diagonal braces.
The foundation formwork for a more typical residential structure is shown in Figure 8-36. The smaller foundation requires fewer horizontal levels of walers, no strong backs, and smaller and fewer diagonal braces. The forms also use the less costly plywood rather than the coated plyform material.
Foundations can be formed using a commercial form system. These types of forms are typically easier to set up and take down than those that are made of plywood or plyform material. They are also usually more rigid and require less in the way of bracing material (Figure 8-37). Most often, a specialty concrete subcontractor would utilize this type of formwork because a full set of forms for even a small residential project is costly to purchase.
Snap ties are the mechanical fasteners that are used to temporarily hold formwork together while the concrete is being placed. They are also used to hold the form material a consistent distance apart resulting in a concrete wall of a specific thickness. Snap ties are engineered so that a portion of each tie remains inside of the concrete wall after it is completed and cured and the remaining portion, which extends outside of the concrete, is snapped (broken) off and disposed of. Different styles of formwork require different types of snap ties.
Wire Type with Plastic Cone Snap Ties
Figures 8-38 to 8-41 show examples of a typical wire type of snap tie with a plastic cone that is commonly used in plywood and plyform foundation formwork construction.
Flat Type Snap Ties
Flat type snap ties are commonly used in manufactured form systems. Figures 8-42 to 8-45 show examples of flat type snap ties and their usage in formwork. Typically, the forms and snap ties are held together using some form of wedges and pins.
Snap Tie Clamps and Wedges
The majority of concrete foundation formwork materials can be salvaged and reused many times before it becomes worn out. Snap tie clamps or wedges are used to hold the formwork together. They clamp on each side of the formwork and hold the form sides tight to the snap tie. This allows the forms to be spaced a specific distance apart and helps prevent the forms from bowing due to the outward pressure of the concrete as it is placed. Often, the snap tie clamps also attach to the walers or strongbacks to provide additional bracing and allow the forms to be straightened. Snap tie clamps are reusable items and are salvaged, cleaned up, and reused many times. Generally, two snap tie clamps are needed for each snap tie used in the formwork as both sides of the forms are clamped. Although the clamps are reused, it is often appropriate to add an amount to the estimate for each snap tie. They often have to be rented, or if already owned, they need periodic replacement.
Figure 8-46 shows clamps attached to concrete formwork and the walers. Several styles of snap tie clamps are used in concrete forming. The types used are often dependent upon the form material style. Figure 8-47 shows Jahn style clamps ready for reuse.
Walers are the horizontal members that are used to straighten and brace the foundation forms and keep them from bulging. The quantity of walers used depends upon the formwork system type and the height of the forms. They are reusable items, but a percentage should be included in the estimate to account for usage and wear of form walers. Figure 8-48 shows several types of form systems with the walers.
Strongbacks and Bracing
Strongbacks are vertical bracing members that are used to strengthen and stiffen the forms. The need for strongbacks depends entirely on the type of forming system and the height of the forms. Often, in a residential setting, strongbacks are not used at all. Bracing is the use of diagonal members to straighten and brace the forms. Turnbuckles are frequently attached to either end of the brace that can be used to micro adjust and straighten the forms (Figure 8-49).
Steel reinforcing is often placed in concrete foundation. The size, layout, and quantity of the steel is determined by the engineering needs of the foundation. In a residential setting, the steel reinforcing requirements are often determined by the building code and are specified in the plans and specification. The reinforcing needs may be such that it will need to be designed by an engineer. The rebar in foundations is often placed in a grid formation of both vertical and horizontal rebar, which can also include multiple grids of horizontal and vertical rebar. Figure 8-50 shows a residential foundation with a grid of vertical and horizontal rebar.
Figure 8-51 shows a commercial building foundation with a double grid of closely spaced horizontal and vertical rebar.
Figure 8-52 shows an example of the concrete foundation section that specifies a maximum rebar spacing of 32″ O/C spacing.
Figure 8-53 shows a three dimensional graphic of the foundation with three rows of horizontal rebar and 80″ lengths of vertical rebar tied to the vertical footing rebar.
Foundation Horizontal Rebar
There are often multiple rows of horizontal rebar in a foundation. The placement of these may be specified by the on-center spacing requirements outlined by the building code, or there may be specific engineering requirements for the placement of the rebar and the maximum or minimum amount of concrete coverage. For example, two addendums to the Rexburg building code make modifications to the International Residential Code and state the following:
“Section R404.14. Delete: Entire section. Insert: All concrete or masonry foundation walls constructed at a height equal to or lower than 4′ shall be constructed with a minimum of #4 rebar spaced at 24″ o.c. horizontally and #4 rebar spaced at 48″ o.c. vertically. The vertical bars shall have a minimum bend of 6″ with the bends rotated in each alternately in each direction.”
These codes determine both quantity, size, and placement of rebar requirements in both the footing and foundation.
The horizontal rebar quantity would be calculated by determining the number of rows required and multiplying this by the length of the foundation wall. Considerations will also need to be made to account for the lapping requirements when tying the rebar together and an appropriate waste factor.
Foundation Vertical Rebar
The vertical rebar in the foundation is usually placed as an extension to the vertical rebar placed in the footings. Each vertical footing rebar would have an additional piece of vertical rebar tied to it to extend the rebar grid to the top of the foundation. The length of each foundation vertical piece is determined by the exposure amount of the rebar in the footings, the height of the foundation, the rebar lapping requirements, and the amount of rebar coverage at the top of the foundation. Figure 8-23 shows a graphic of the footing, including vertical rebar where the exposure amount is 25″. Figure 8-52 shows a graphic of the foundation including vertical rebar. The foundation height is eight feet and the maximum embed distance at the top is identified as three inches. The formula for determining the length of the vertical rebar in the foundation would be as follows:
Foundation Height – Footing Exposure Amount – Maximum Embed Distance + Rebar Lap Length
8′-0″ – 25″ – 3′ + 12″
96″ – 25″ – 3″ + 12″ = 76″
The length of a normal 20-foot piece of rebar would be divided by the 6.67-foot length of each piece and would be as follows:
20′-0″ ÷ 6.67′ = 3 Pieces
This would be rounded down to three even pieces and would yield
20 ft ÷ 3 = 6.67 ft.
The total number of 20-foot pieces of rebar that would need to be purchased could be determined by multiplying the 6.67-foot length by the number of vertical pieces.
Very often in construction when the foundation is only a few feet tall, as is shown in Figure 8-54, the vertical rebar in the footings is extended to the top of the foundation and the vertical rebar requirements for the foundation are calculated as part of the footing rebar requirements and no additional rebar is added for the foundation.
Anchor bolts are used to attach the structure to the foundation. They are embedded in the foundation concrete while it is still in a plastic state. Specific anchor bolt size, embed distance, spacing, and plate washer requirements are specified by the building code and are usually detailed in the plans and specification. The foundation wall section, shown in Figure 8-52, shows the foundation anchor bolts and specifies a maximum spacing of 6′-0″ on-center. In addition to the on-center spacing requirements, there is a requirement for an anchor bolt at each end of the mud sill and at each corner (Figures 8-55 and 8-56).
Earthquake straps or hold-downs are hardware connections that attach the walls more firmly to the foundation. In houses located in earthquake prone zones, such as those specified by the IRC as zones D, E, and F, additional attachments will need to be provided. The earthquake straps help resist the lateral and sliding loads that are placed on the structure in an earthquake (8-57).
One common type of earthquake strap is placed at the building corners and at the edges of doors and windows. The strap anchors are embedded in the foundation concrete. The straps extend above the foundation to the wall framing, and they are attached by nailing to the studs in the walls above. When nailing the straps to the wall framing, it is required that all nail holes in the strap be filled. Usually two studs are needed in the wall framing to meet the nailing requirements. Very often, the straps are placed in locations where there are already double studs such as corners or the edges of windows and doors (Figure 8-58).
Foundation Dampproofing and Waterproofing
Although the terms dampproofing and waterproofing appear to be similar, there is a distinct difference between the two.
Dampproofing is intended to keep soil moisture out of a building, while waterproofing is intended to keep out both moisture and liquid water. The IRC section 406.1 requires that “foundation walls that retain earth and enclose interior spaces and floors below grade shall be dampproofed from the top of the footing to the finished grade.” A number of materials can be used for dampproofing, including bituminous coating (tar), acrylic modified cement, and surface bonding cement. The coating can be applied by a paint roller, brushing, or spraying. Dampproofing is usually estimated as a square footage cost by determining the square footage of area to be covered and the coverage rate of the dampproofing material (Figure 8-59).
Foundation waterproofing is a more rigorous process than dampproofing. The process is intended to create an impermeable barrier for the liquid water in situations such as high groundwater.
Waterproofing is required by the IBC “in areas where high water tables or other severe soil-water conditions are known to exist” (R402.2). Waterproofing is a more intensive process that usually requires some form of membrane coating. The IBC specifies that “the membrane shall consist of 2-ply hot mopped felts, 55-pound roll roofing, 6 mil polyvinyl chloride, 6 mil polyethylene or 40 mil polymer-modified asphalt” (R402.2).
Many waterproofing systems are proprietary products that require the application be installed by a certified applicator in order to warrant the product. The waterproofing system usually consists of more than just a water resistive barrier but could also contain other elements such as drainage mats and pipes. Waterproofing materials can include cementitious products, liquid membranes, sheet membranes, built-up systems, and bentonite. Estimating waterproofing will usually require pricing with a subcontractor.
Estimating Dampproofing and Waterproofing
Dampproofing and waterproofing is usually estimated based upon a square foot cost or a cost per square (100 SF). The calculations are based upon the length of the area to be dampproofed or waterproofed and the height of the treatment. Usually, the area of the windows or other openings are subtracted from the total area.
Foundation insulation is very often installed in order to increase the energy efficiency of the structure. There are a number of methods for installing the insulation. One method that is used on basement and crawlspace construction is to install wood framed walls inside of the foundation and attach the insulation material to the wood framing. This type of insulation would be installed later in the construction process and is not typically estimated during the concrete phase of the estimate. Figure 8-60 shows wood-framed basement insulation walls on the concrete foundation walls, which have insulation installed in the completed framing.
Rigid sheet insulation is often installed to insulate concrete foundations. The insulation can be installed either to the interior or the exterior of the foundation. It is most often placed on the interior when the foundation is buried in the earth and supporting a concrete slab floor. This helps to separate the heated interior space from the cold, damp earth. The insulation can be installed along the foundation walls and also under the floor slab. Figure 8-61 shows workmen installing rigid polystyrene foam along the inside of concrete foundation walls.
Rigid foam insulation can be installed on the exterior of the foundation walls. If the insulation extends past the finished grade and is exposed, it will need to have some type of protective surface installed over it, such as metal or cement parging.
Parging or pargeting, as it is sometimes called, is a thin cementitious mortar that is troweled on concrete or masonry walls to cover and smooth the imperfections in the surface such as snap tie holes, concrete form seams, and voids. Parging also adds a measure of protection and waterproofing to the walls. Parging can be purchased in premixed powders that are mixed with water to make a cementitious paste. The parging can be mixed from scratch with fine sand, often called silica sand, and cement powder. Liquid adhesives, or acrylic admixtures, can be added into the mix to improve adhesion and strength. The parging is usually troweled onto the walls and smoothed out with a rubber float. The parging is usually only installed on the foundation above grade on exposed areas. Commonly, a foundation will have dampproofing or waterproofing below the grade and have a parging coat on the foundation above the grade. Parging is usually estimated by determining the square footage of the parging area and pricing per square footage. Openings such as doors and windows are usually subtracted from the square footage of parging area.
Foundation Material Costs
This section will focus on preparing the concrete foundation material estimate. The emphasis will be on creating an assembly estimate from the various elements that are part of forming, placing, and stripping concrete foundations.
An explanation for each of the necessary variables to create your assembly is as follows:
SF Foundation Blockouts. This variable is used to input the square footage of openings such as doors and windows that are created in the foundation at the time the concrete is placed. The blockouts can be made of wood or metal materials and prevent the area from being filled with concrete during the pour. The square footage of the blockouts will be subtracted from the square footage of foundation area and will subtract a quantity of concrete from the cubic yards concrete total. Figure 8-64 shows a metal window blockout in a concrete foundation, and Figure 8-65 shows a blockout in the garage foundation for the installation of the garage door.
Vertical Rebar Spacing.This variable accounts for the spacing of the vertical rebar that is installed in the foundation. Usually the spacing is the same as the vertical rebar spacing in the footings, which in this case is 32″ or 2′-8″.
Vertical Rebar Length. This variable accounts for the length of the vertical rebar that is tied to the vertical rebar in the footings. Figure 8-81 shows the vertical rebar in the foundation, which was calculated at 80″ or 6′-8″.
Number of Horizontal Rebar.This variable accounts for the number of rows of continuous horizontal rebar that is installed in the foundation. This number was previously calculated at three.
Rebar Lap Length.This variable accounts for the code required 24 bar diameter lapping length when the rebar sections are tied together. The rebar that is installed in #4 rebar and the lapping length would be calculated at 4/8″× 24 = 12″. This is converted to a 1-foot measurement and entered into the header.
Foundation Bolt Spacing.This variable accounts for the spacing of the foundation anchor bolts that are installed in the top of the concrete foundation. The code required 6′-0″ on-center spacing will be input into the header section.
Foundation Mudsill Material Length.This variable accounts for the length of the mudsill material that will be bolted to the foundation. The number will be used to calculate the extra mudsill bolts that are required on each mudsill end.
Number of Corners and Intersections.This variable adds an additional foundation anchor bolt in the corners and intersection of the foundation where additional bolts are required.
Foundation Dampproofing Height. The foundation dampproofing height is the distance that the dampproofing material extends from the top of the footings to the finished grade. In this case, the top one foot of the foundation is exposed, so the dampproofing height is entered at 7′-0″.
Rigid Insulation. This variable is the amount of rigid insulation that will be used. If the concrete foundation does not have any rigid insulation installed, then a zero is inputted. If it has rigid insulation on either the inside or outside of the foundation, then a one is inputted. A two is inputted if insulation is installed on both the inside and outside of the foundation.
Rigid Insulation Height. If the foundation has insulation installed, this variable allows for the height of the insulation.
Foundation Parging Height. This variable allows for the height of the cement parging. This is usually the height from the top of the foundation to the finished grade.
Other Information. Other information such as number of vertical rebar, SF foundation area, square feet of contact area, and cubic yards of concrete is calculated from the variables above and your building plans.
With these variables, you can calculate the quantities of foundation materials.
Foundation Concrete Quantity Formula
The formula for calculating the foundation concrete is to multiply the cubic yards concrete by the waste factor, and the total is divided by the size of the material, which in this case is one cubic yard. The total should be rounded up to the nearest quarter of a cubic yard. This is because concrete is usually purchased in 1/4 cubic yard increments (Excel Figure 8-29).
Horizontal Reinforcing Quantity Formula
The basic formula for calculating horizontal reinforcing material is performed by multiplying the foundation length by the number of horizontal rebar and the waste factor. The total is divided by the rebar size minus the rebar lap length.
Vertical Reinforcing Quantity Formula
The formula for calculating the vertical reinforcing quantity is performed by multiplying the number of vertical rebar by the vertical rebar length and the waste factor. The total is divided by the rebar size.
Foundation Bolt Quantity Formula
The foundation bolt quantity is calculated with the following formula:
((Foundation Length ÷ Foundation Bolt Spacing) + Number of Corners and Intersections + (Foundation Length ÷ Foundation Mudsill Material Length)) × Waste Factor
Foundation Rigid Insulation Quantity Formula
The foundation rigid insulation quantity is calculated with the following formula:
((Rigid Insulation × Rigid Insulation Height × Foundation Length) ÷ (Area of One Sheet of Rigid Insulation)) × Waste Factor
Remember, rigid insulation in the formula above is the amount of insulation installed. If there is insulation on one side, this variable will be a 1. If there is insulation on both the inside and the outside, this variable will be a 2.
Shallow Foundation Wall Costs
This will be completed in a fashion similar to what was done with the basement foundation walls.
Complete the shallow foundation materials estimate using information from the basic takeoffs and details in the plans and specification. Apply the same principles and formulas learned in previous portions of the estimate to estimate the shallow foundation wall.
Completing the Miscellaneous Foundation Material Costs
The miscellaneous foundation material costs section will include material for both the basement and shallow foundations. The items estimated include plywood forming material cost, earthquake straps, foundation dampproofing, foundation parging, and window bucks (Figure 8-44).
Foundation Form Material Costs
In this instance, the material cost for forming the foundation will be taken from the residential section of the NCE. NCE Figure 8-4 shows a screenshot of this section.
The information in the description explains that the costs described are for forming walls with plyform material and includes all material cost for forms, bracing, snap ties, clamps, etc. The unit of measurement identified is the square footage of the contact area and explains that both sides of the forms should be used. The material costs are based on the number of times that the forms will be used or reused. For this example, five uses will be selected. The size is 1. The unit is SFCA, and the material cost is identified as $0.80 per SFCA.
Foundation Earthquake Anchors
Figure 8-66 is a graphic of the foundation with earthquake straps installed. They are usually installed at the corners of the foundation and at the side of large openings, such as would be required for a garage door.
Foundation earthquake straps are a count and list items taken from the plans. Their location would usually be specified on a foundation plan. They may be detailed on the plans by either a symbol or a text note. If the connector is identified using an annotation symbol, there will be an annotation legend on the plans showing what each symbol means (Figure 8-67).
Figure 8-68 is a foundation detail showing two earthquake straps. One is identified with a text note and the other by using an annotation symbol. Normal drafting convention would use one or the other, not both.
Foundation dampproofing will be installed on the foundation walls that enclose the living area of the basement. Dampproofing starts just below the finished grade and extends down to the top of the footings. The distance the foundation extends above grade can vary greatly, however, the minimum distance that the foundation extends above grade is six inches. The actual distance depends greatly upon the actual terrain and building conditions. For this example, we will assume that the foundation extends 12 inches above the grade, and the dampproofing will start two inches below the grade or 14 inches below the top of the foundation. Dampproofing will not be installed on the garage portion of the foundation that does not enclose living space.
The area dampproofing covers is the length of the enclosed foundation multiplied by the height. Windows and other openings will be subtracted from the total. Figure 8-69 shows the foundation dampproofing that is 82 inches high. The length is the total length around the foundation.
The foundation dampproofing length would be
36′+ 32′+ 10′-3″ + 6′-3″ + 11′+6′-3″ + 14′-9″ + 32′= 148′-6″
The foundation dampproofing area would be
148′-6″ × 6′-10″ = 1,074.75 ft2
The dampproofing is typically held back about three inches from the edge of the windows. This area would be 3′-9″ × 4′-6″. The calculated area would be multiplied by the number of windows, which is three.
3′-9″ × 4′-6″ × 3 windows = 50.625 ft2
This is subtracted from the total as follows:
1,074.75 ft2 – 50.625 ft2 = 1,024.125 ft2
Foundation parging is commonly done on the foundation area that is exposed above the grade and exposed to view. As was previously determined, the dampproofing is just below the finished grade. The parging will cover the area from the top of the dampproofing to the top of the foundation, or 14 inches. The length of the parging will be the length of the foundation that has parging. This will also include the area of the parged garage foundation (8-70).
The foundation dampproofing parging length will be
36′-4″ + 22′+ 20-′4″ + 10′ + 10-′3″ + 6′-3″ + 11′-0″ + 6′-3″ + 14′-9" + 32′ = 189′-2″ ft2
The area of the window and door openings will be subtracted from the total area.
Garage door opening 1′-2″ × 16′ = 18.67 ft2
Garage entry door opening 1′ × 3′-2″ = 3.17 ft2
Window openings 6″ × 4′ × 3 windows = 6 ft2
18.67 ft2 + 3.17 ft2 + 6 ft2 = 27.85 ft2
This is subtracted from the total.
189′-2″ ft2 - 27.85 ft2 = 161.32 ft2
Steel Window Bucks
The steel window bucks are a count-and-list item. If it was determined when completing the basic takeoffs that there were three basement windows 4′-0″ × 4′-0″, three window bucks at that size would be included in the estimate (Excel Figure 8-49)
Programing the Concrete Foundation Labor Costs
The concrete foundation labor costs will be estimated using the National Construction Estimator. The labor cost will be a combined cost for both the basement and shallow foundations..
The labor cost for plywood forming will be taken from the residential section of the National Construction Estimator. NCE Figure 8-5 shows a screenshot of the plywood forming subsection.
The labor costs for plywood forming is priced per square foot of contact area.
Concrete Reinforcing Steel
NCE Figure 8-6 shows a screenshot of the NCE concrete reinforcing steel section. The costs are priced both by the pound and lineal foot. The price per lineal foot will be used.
The lineal footage of footing rebar is calculated by multiplying the total lineal footage rebar purchased by multiplying the number of 20-foot lengths of rebar for the horizontal and vertical rebar in both the basement and shallow foundations.
Placing Concrete Walls
NCE Figure 8-7 shows a screenshot of the Concrete Walls subsection of the residential section of the NCE, which will be used to price the labor costs associated with placing concrete walls for the foundation.
The introduction provides information about methods used to price the labor cost, including information that the labor unit is per square foot of wall area measured from one face only.
NCE Figure 8-8 shows a screenshot of the Foundation Bolts subsection of the residential section of the NCE, which will be used to price the installation of the anchor bolts labor costs of the foundation.
Foundation bolts are priced both per each and pack of 25.
NCE Figure 8-9 shows a screenshot of the extruded polystyrene insulation panel portion of the insulation subsection of the residential section of the NCE, which will be used to calculate the insulation cost.
Foundation insulation is priced per square foot. The quantity of rigid insulation will be zero if there is no insulation on the project.
NCE Figure 8-10 shows a screenshot of the hold downs portion of the Framing Connectors subsection of the residential section of the NCE, which will be used to calculate the earthquake strap cost.
The earthquake anchors are priced per each.
NCE Figure 8-11 shows a screenshot of the Dampproofing subsection of the Thermal and Moisture Protection section of the commercial section of the NCE, which will be used to calculate the dampproofing cost.
The dampproofing is priced per square foot.
NCE Figure 8-12 shows a screenshot of the Parging (pargeting), Waterproofing and Dampproofing subsection of the masonry section of the commercial section of the NCE, which will be used to calculate the dampproofing cost.
The parging is priced per square foot. Estimate example 8-4 shows the completed foundation labor costs.
Two primary classifications of concrete flatwork are cast on earth flatwork and suspended flatwork. Cast on earth flatwork is directly supported upon the earth and includes garage floors, basement floors, slab on grade floors, sidewalks, driveways, patios, and equipment slabs. Suspended concrete flatwork consists of structural slabs used in concrete multi-story construction. In residential construction, suspended concrete slabs are occasionally used in situations where an exterior porch is built on top of a basement foundation room such as a storage room.
Cast on Earth Flatwork
Cast on earth flatwork is generally composed of several separate and distinct layers. Even the most basic concrete flatwork cast directly on the native soil has two layers: the concrete slab and the supporting native soil. Figure 8-71 shows an example of a concrete floor cast directly upon the earth.
The supporting native soil is an important part of a concrete flatwork system. If the native soil is sufficiently compacted and stable, the slab can hold up well, but in many cases, native subgrade soil does not provide an ideal base for the concrete. Many concrete floor systems can be improved by the addition of a subbase material. Desirable subbase material is a layer on top of the subgrade that is composed of compacted granular fill material that can be trimmed and graded easily. Some examples of desirable subbase material include gravel, crushed stone, and road base.
Gravel is composed of small rocks that are naturally formed by weathering and erosion. The rock typically has a rounded smooth shape. Gravel is graded, so the batch is uniform size, which is achieved by sending the rock through a specific screen grid size. Common sizes of gravel would be 1-inch, 3/4-inch, or 3/8-inch gravel. The small 3/8 or smaller is sometimes called pea gravel (Figure 8-72).
Crushed stone is a granular gravel-like material that is formed by crushing larger rocks into smaller pieces. Crushed stone is sized and graded similarly to gravel but has sharper more angular edges as a result of the crushing the larger rocks into smaller sizes. Crushed stone is graded and sized similar to gravel (Figure 8-73).
Road base is comprised of gravel or crushed stone with the addition of fines such as sand and a clay binder material. Road base can be moistened and compacted to provide a stable base that holds its shape for the concrete layer. Road base can be called other things such as road mix, pit run, bank gravel, and crusher run, depending upon how the material is processed.
Figure 8-75 shows an example of a concrete floor on a subbase of compacted road base material.
Figure 8-76 shows a garage floor that has a layer graded subbase installed and smoothed ready for the concrete layer.
Figure 8-77 shows an example of a basement floor that has a subbase of compacted road base installed and graded ready for the concrete floor. This floor also has portions excavated for a thickened slab that will be used as a support for load bearing walls installed on the top of the floor. The compact road base material is able to hold its shape for the thickened slab footing depressions.
More complex cast on earth floor systems can have additional layers, such as vapor barriers, insulation, and reinforcing. Concrete floors wick moisture out of the soil, which can increase the relative humidity in a building making the space feel cold and damp. Often a vapor barrier is placed on the soil or subbase before placing the concrete. Vapor barriers are commonly made of polyethylene plastic, which is sold in different thicknesses measured in mils. Common vapor barriers would have a thickness of four or six mils. The vapor barrier can significantly reduce moisture migration into the building from the concrete floor.
In addition, rigid foam insulation can be installed to increase the energy efficiency of the structure and slow down the transfer of heat. Rigid foam insulation appropriate for under slab installation is extruded polystyrene foam, as opposed to expanded polystyrene, which shouldn’t be used in an under slab installation. Common brands of extruded polystyrene include pink colored foam from Owens Corning and blue colored dow styrofoam (Figure 8-76).
Additional elements of a cast of earth floor system include formwork, reinforcing, isolation materials, and concrete.
Concrete Flatwork Formwork
The formwork for concrete flatwork in residential construction is often made of two-by-four or two-by-six material. Some flatwork types such as basement and garage floors that are inside of foundation walls require little formwork. Other flatwork such as sidewalks and driveways can require more extensive formwork.
Sidewalks and driveways typically require formwork on each side and ends.
Formwork for curved shaped forms require material that can be bent and formed. It can be one by material or even thinner bender board. Figure 8-81 shows an example of the formwork for a curved sidewalk.
Formwork often also requires the use of forms to screed and level the concrete in addition to the forms that define the exterior shape. The screed forms are staked in the center of the form and carefully leveled and straightened. The concrete is placed and raked as smooth and level as possible. A straightedge is pulled across the screed board forms to further level and smooth the slab. After the concrete has had a chance to set slightly, the screed form boards are removed, and concrete is shoveled into the gaps and leveled again.
Concrete Flatwork Reinforcing
Reinforcing can be installed in concrete flatwork to strengthen the slab. Two types of reinforcing that can be installed are steel rebar and welded wire mesh. Rebar is often installed in a grid pattern with lengths of rebar running each way. Figure 8-83 shows an example of a sidewalk slab with an 18-inch grid of number four rebar.
Another type of flatwork reinforcing is welded wire mesh, which is also known as welded wire fabric (WWF). Welded wire fabric is purchased in rolls or sheets of wire mesh formed into a grid pattern, which is specified by combining the grid spacing in inches and the wire cross sectional area in hundredths of square inches. Common sizes specification would include 6 × 6 -W1.4/W1.4 or 4 × 4 W4.0 × W4.0. Figure 8-84 shows an example of a sidewalk with welded wire fabric installed prior to placing the concrete.
At times, it is desirable to isolate or separate two concrete slabs from each other. One reason for this is to prevent cracks in one slab from telegraphing to the other. To isolate the slabs from each other, material is placed between the two slabs to separate them. This is commonly known as expansion material or an expansion joint. Some common expansion materials include asphalt impregnated fibrous material, rubber, wood, and other synthetic materials. It is typically sold in widths suitable for concrete flatwork and lengths or rolls. Figure 8-85 shows an example of asphalt impregnated fibrous isolation material installed between an existing concrete slab and a new concrete slab.
Concrete used for flatwork construction should be strong and durable. The concrete should be ordered with a compressive strength between 3,500 and 5,000 psi. The procedure used when placing and finishing the concrete is also important and can dramatically impact the final strength. Concrete that is less stiff and more fluid is easier to place and finish, however, adding water to the concrete to improve the workability can affect the concrete strength as the water/cement ratio in the mix is an important factor in determining the ultimate strength of the concrete.
Testing Concrete Strength
A test that is used to sample the water/cement ratio in a concrete mix is known as a slump test. This is done by filling a 12-inch cone full of fresh concrete directly from the ready-mix truck. The concrete in the cone is consolidated and air gaps removed by agitating it with a metal rod. The concrete is smoothed off level with the top of the cone and the cone carefully lifted off the pile of concrete. The amount that the concrete slumps down from the top of the cone determines the concrete slump and indicates the consistency of the concrete. Flatwork concrete should be placed at a slump consistency between one inch and four inches (Figure 8-86).
Additional water can be added to the concrete mix by the ready mix truck. However, adding too much water at the site will irrevocably impact the concrete strength. Because it is easier to place and work concrete, workers often have additional water added on the site. Adding one gallon of water per cubic yard can increase the slump by as much as one inch and lower the compressive strength by as much as 200 psi.
Calculating Concrete Quantity
Concrete for flatwork is calculated by the cubic yard as measured by the thickness, width, and length of the slab. A waste factor is also usually included in the calculation. The amount of waste factor is dependent upon the grading of the subgrade or subbase. Carefully leveled and graded subbase will allow for a smaller waste factor such as five percent. Inaccurately graded subgrades may require a waste factor of 10 percent or more. The final quantity will need to be rounded up to the next quarter yard increment.
Another factor that can impact the strength of concrete flatwork is the curing process that it goes through. The hydration process is affected by the temperature of the concrete and the time that the water has to combine with the cement before it evaporates. One method of curing the concrete is to apply a liquid curing compound to the surface for the slab. Concrete cure is a commercial product that is typically applied to the slab with a pump type sprayer. Concrete curing is calculated by determining the number of square feet that a gallon of cure will cover.
Calculating Concrete Floor, Sidewalk and Driveways Material Costs
CalculatingConcrete Floor Costs
To calculate the cost of the concrete floor, you will need to know the variables for the floor thickness, floor area, thickened slab cross sectional area, thickened slab length, lineal feet of rebar, reinforcing mesh, lineal feet of forms, lineal feet of expansion material, vapor barrier, concrete curing, and fill material depth.
The floor thickness for the basement floor can be determined from sectional views of the foundation. Figure 8-88 shows a sectional view of the foundation including the basement floor, vapor barrier, and the floor fill material. The floor thickness is identified as four inches, the vapor barrier is identified as a six mil polyethylene barrier, and the fill material as eight inches of compacted fill.
For this example, we will use the basic takeoffs of a basement floor area that is 1,120 square feet and a garage floor area of 440 square feet, as is shown in Excel Figure 8-58.
Thickened Slab Cross Sectional Area and Length
Thickened slab cross sectional area and length are for inputting information about thickened slab footing under the concrete floor. In this situation, the thickened slab and floor are placed in one monolithic pour. Figure 8-89 shows a basement floor with thickened slab areas excavated.
Thickened slabs are often shaped like a trapezoid, as is shown in Figure 8-90. The cross sectional area is calculated by finding the average horizontal width and multiplying by the footing height.
The calculation to determine the average width is determined by adding the width of the footing at the top to the width of the bottom and dividing the sum in half.
Average Width = (1'-6" + 1'-0") ÷ 2 = 1'-3"
Cross Sectional Area: 1'-3" x 0'-8" = 0.833 ft2
The length of the thickened slab footing is determined as 14′ – 5″ by the floor plan view of the basement, as is shown in Figure 8-91.
In this instance, the footing is not a thickened slab area, and the footing supporting the basement load bearing wall is an interior grade footing and was previously calculated, as is shown in Estimate Example 8-1.
Rebar and Reinforcing Mesh
The information about lineal feet of rebar for the floor is inputted into the header section. This is done by making a manual calculation. For example, Figure 8-92 shows a section view of a front porch that has a rebar grid spaced six inches on-center. The length of the rebar going each direction will need to be determined from a plan view. The number of pieces in each direction will need to be determined. The total of all of the pieces determine the total lineal footage.
Some slabs do not include reinforcing mesh. The requirements to install reinforcing mesh are usually shown using symbolic representations or annotations in detailed section views, as is shown for the patio in Figure 8-93. The adjacent floor in the garage does not have reinforcing mesh.
The area of the patio is determined by the site plan view. Figure 8-94 shows an example site plan view. The area is calculated by multiplying the length and the width.
Patio length × Patio width
20' x 16' = 320 ft2
This would be the quantity used to calculate the reinforcing mesh quantity.
Lineal Feet Forms
The lineal feet of forms are determined by the need and what would be best coordinated with the concrete installers. Basement floors are often placed without the use of additional forms or screed boards. The garage floor would need forms across both door openings but could be placed easily without the use of other forms or screed boards. The concrete patio in Figure 8-94 would need forms around the outside of the slab that would be calculated as follows:
12 ft + 20 ft + 12 ft = 44 ft
LF Expansion Material
Expansion material would be used typically to isolate two separate concrete slabs from each other. Expansion material could be used on the patio in Figure 9-94 between the slab and the house. At a minimum, it would be needed between the patio and the adjoining concrete garage floor. In addition, expansion material would be placed between the front of the garage floor and the driveway.
Some floors and slabs do not have a vapor barrier. If there is a vapor barrier, the quantity would be determined by the square foot of floor or slab area. Figure 8-88 shows a six mil vapor barrier underneath the basement floor slab.
Some concrete floors and slabs do not use concrete curing. If they do, the quantity is determined by the square foot of the floor or slab area.
Fill Depth Material
The fill depth input in the header section allows for input of the thickness of the floor or slab fill depth in inches. When fill is utilized, the depth of the fill is inputted and the square footage of the floor or slab area is used to calculate the cubic yards of fill material. All concrete floors or slabs will have fill material installed to a depth as shown in the section or detail views. When the depth of the fill is inputted, the square footage of floor area from the header section is used to calculate the cubic yards of fill material.
Estimating the Concrete Floors Labor Costs
Both the concrete floor, sidewalk, and driveway labor cost estimates can be completed using the Slabs, Walks, and Driveways subsection of the National Construction Estimator. NCE Figure 8-13 shows an example of this subsection. The cost is based upon the square footage of the concrete flatwork and includes the labor to form, place, and strip the slab. The labor for the four-inch-thick option is shown at $2.52 per square foot.
Concrete steps are created by erecting formwork to hold and shape the unsolidified concrete, placing the concrete in the forms, and allowing it to set to a point that it will hold the desired shape but is still pliable. At that point, the forms are stripped away, and the final floating and troweling of the surface is done to provide for a consistent finished surface.
Concrete steps can be placed directly upon the earth, or they may be constructed in such a way that they are constructed as a self-supporting unit known as a suspended stairway. In either case, formwork will need to be fashioned before the stair concrete can be placed.
Casts on Earth Stairs
Casts on earth stairs are placed by placing the concrete directly upon the earth. With this type of construction, a base of solid compacted fill is required under the stairs to provide support and keep them from settling. Often, additional fill will be placed under the stairs to serve as a replacement for some of the concrete material when the steps are thick. Casts on earth concrete stairs may be placed between existing concrete walls on one or both sides, or they may be placed as a single monolithic unit.
Casts on Earth Stairs Between Existing Walls
Figure 8-95 shows an example of the formwork for concrete stairs formed between two existing walls.
Compacted fill was placed under the stairway and shaped to the desired slope. This stairway also has polystyrene foam insulation placed between the earth and the stairs as heating tubes will be cast into the concrete to keep the stairs free of snow and ice in the winter. The individual steps were formed by staking riser form material at each tread level. The concrete will be placed in the forms and allowed to harden to a point that the riser forms can be removed. The holes left by the metal stakes will be filled, and the workmen will finish the top and face of the stairs.
Casts on Earth Stairs with Open Ends
Stairs with open ends will also require end panels. Smaller stairs with two or three steps may be able to use a single piece of plywood at each end, or more extensive end formwork may be required. Figure 8-96 shows an example of the formwork for a small two-step concrete stair, such as would be used to walk up to the front porch of a house.
The small stairway will require six pieces of material, including two form sides, two riser form pieces, and two ledger boards. Although there are no dimensions other than the 36-inch width, the relative size of the pieces can be determined. Code requirements specify that the maximum riser height of 7-3/4″ and a minimum run of 10″ are likely less than 12″. The height of the plywood form sides can be determined by multiplying the two 7-3/4″ maximum riser heights to equal 15-1/2″. The length of the plywood form sides would be determined by multiplying the two run lengths of 12″ to equal 24″. One piece of plywood 16″× 48″ would make both plywood form sides. Two pieces of 2 × 8 framing lumber three feet long would make both of the riser form fronts. Two pieces of 2 × 4 framing lumber 16 inches long will make the ledger boards.
Larger stairs such as in Figure 9-97 will require more extensive formwork.
This larger set of forms will require more extensive formwork material. The dimensions of the stairs are 72 inches wide and 78 inches long and 37-1/2″ tall. To construct the form sides, the following will be needed:
2 pcs 3/4″ × 4′ × 8′ plywood
4 Pcs 2×4 × 78″ plates
12 pcs 2×4 × 36″ studs
2 pcs 2×4 × 54″ form bracing
The form risers are approximately 72 inches long. The front riser form is a little longer, and the 2 × 8 step form is a little shorter, but they could be averaged at 72 inches. Ten six-inch blocks are also needed to support the riser forms, but the assumption can be made to use scraps from the form side studs. The totals would be as follows:
6 pcs 2×8 × 72″ riser forms
Porch and Landings
Often, a building will have a front porch or landing that will need to be formed and placed at the same time as a stairway. The large set of stairs previously shown in Figure 8-97 was formed and placed as one monolithic pour separate from the building foundation. Often, the porch will have a foundation underneath it that will require a concrete porch on the top of it. The foundation may be a shallow foundation that will be backfilled and the porch placed on top of the fill. See Figure 8-98.
The foundation for this kind of porch will be backfilled, and the formwork will consist of two-by-four ledger boards that are attached to the foundation wall. Attached to the ledger material, two-by-ten form material will be used for the porch edge. In the case of a small step, such as in Figure 8-99, two-by-six or two-by-eight material would be used to form the step.
Figure 8-100 also shows where a porch such as this has been placed and the porch edge formwork stripped. The ledger board is still attached to the foundation.
Other times, the foundation will be the full depth of the basement with the expectation that a suspended concrete porch slab will be placed upon the top and room created underneath the porch will serve as a basement storage room such as is shown in Figure 8-99.
The suspended porch slab shown in Figure 8-101 will require additional reinforcing to support it. The rebar extending from the foundation walls will be bent over and placed in the porch slab and be incorporated into the reinforcing rebar mat in the concrete cap. The same porch edge forms, ledger strip, and step edge forms will be used as the porch for the backfilled foundation. However, a temporary floor and extensive temporary support bracing will need to be installed before placing this style of concrete porch (Figure 8-102).
Estimating the Concrete Steps Costs
To estimate the cost of concrete steps, you will need to know variables for square feet of sectional stair area, stair width, landing area in square feet, and landing area thickness.
Figure 8-103 shows a colored section view of a front porch stair with two stair types: a small two tread front sidewalk step and a front porch with a single step to the front door that is poured with the porch as a monolithic concrete pour.
Figure 8-104 shows the same porch and stairs from a plan view perspective.
Determining the Sidewalk Step Variables
The sidewalk step has two variables, SF Sectional Stair Area and Stair Width.
SF Sectional Stair Area
The SF of sectional stair is found by determining the area of the sectional area of the stairway. For example, Figure 8-105 shows the details of the concrete sidewalk step shown in Figures 8-103 and 8-104.
The end view of the small stairs has dimensions of 23½ inches deep and 17 inches tall. Each step has a rise of 6½ inches and a run of 11 inches. The bottom step extends four inches below the riser height to account for the sidewalk depth. The overall width has an extra 1½ inches added to account for the distance the stair extends underneath the porch overhang. The sectional area could be determined using several methods. One method would be to calculate the rectangular area of the bottom step and add the rectangular area of the top step. The small notch in the top of the stairs can be ignored.
Figure 8-105 shows the width of the stairway as 48 inches wide. Multiplying the stair sectional area by the stair width will give you the needed volume of concrete, which in this case is 0.34 cubic yards.
Determining the Front Porch Variables
The front porch includes an entry step, landing, and reinforcing. The entry step and landing will be placed in a single monolithic pour, and the inputs will be a little more extensive. Figure 8-106 shows a three dimensional view of the front porch landing and entry step.
SF Sectional Stair Area
The SF section stair area (Figure 8-103) shows a section view of the front porch. The SF sectional area is the area of the end of the entry step. The dimensions shown are 6¾ inches high by 11 inches wide. Multiplying the height by the width will return the sectional area as follows:
The stair width is shown on Figure 8-104 as 6 feet or 72 inches.
Landing Area (Square Feet)
The landing area is determined by multiplying the width of the landing by the length of the landing. Figure 8-104 shows the dimensions of the landing as 6 feet, 4½ inches wide by 11 feet, 3 inches long. Multiplying the width by the length results in the landing area as follows:
Landing Area Thickness (IN)
The landing thickness is shown in both Figure 8-103 and 8-104 as 7½ inches. Using these variables and the formulas for volume, you will find that a concrete quantity of 1.78 cubic yards is needed for the front porch.
The front porch is a structural concrete slab installed over a basement storage room. A grid of reinforcing rebar will be placed in the porch slab to strengthen it. The rebar grid can be identified in the plans by using several methods. For example, an annotation symbol as shown in Figure 8-106 can be used to specify the reinforcing. The annotation specifies a grid of number four rebar spaced at nine inches on-center, both horizontally and vertically. The annotation in the section drawing shown in Figure 8-104 also identifies a rebar grid of number four rebar spaced nine inches on-center. This annotation also specifies a three-inch rebar cover space. Figure 8-108 shows a view of the front porch with the rebar grid exposed.
The quantity of rebar is calculated by determining the number of horizontal rebar and its length and the number of vertical rebar and its length. The number of horizontal rebar is determined by dividing the porch width by the rebar spacing rounding up to the next whole number.
The 8.5 is rounded up to nine. The length of the horizontal rebar is calculated by subtracting the cover distance of three inches on each end from the overall porch length as follows::
The quantity of vertical rebar is calculated in a similar manner.
In this case, the product is a whole number of 15, however, because of the whole number, an additional rebar will need to be added as a starting rebar for a total of 16. The length of the vertical rebar is calculated by subtracting the cover distance of three inches on each edge by the overall porch width as follows:
The total lineal feet of rebar is calculated as
Determining the Garage Step Variables
The final concrete step to estimate on this project is the garage steps. Figure 8-109 shows a section view of this step with the overall dimensions.
The individual riser height and tread length is not given but can be calculated easily by dividing the total rise by the number of risers and the total run by the number of treads.
The square footage of sectional area can be calculated by multiplying the steps overall length by the steps overall height and subtracting the area of one tread and riser multiplied by three. Figure 8-110 shows the calculations and calculated SF sectional stair area of 3.00 square feet.
The stair width of 40 inches can be determined from the plan view as is shown in Figure 8-111.
Completing the Concrete Steps Material Costs
The concrete material subsection allows for inputs of concrete, reinforcing, step form sides, step riser forms, porch edge forms, porch, porch bottom forms, and form bracing. The material quantities calculated are totaled for all of the concrete stairs in the project.
This is a total of the concrete needed in all of the steps on your project.
The correct reinforcing material is multiplied by the waste factor and rounded up to the next full piece.
Step Form Sides
Both the sidewalk step and the garage step will require form sides. Three quarter inch plywood form material will be used to form the sides of the steps. One method of calculating the amount of plywood for the step side forms is to sketch it out as is shown in Figure 8-112. This shows that approximately one half of a sheet of plywood will be needed to form both the sidewalk step and the garage step sides. Even though plywood can be purchased only in full size sheets, it is likely that at least some of the form sides could be made from scraps on the project.
Step riser forms will be used on all three of the steps. Two-by-eight material will be used to form the stair risers. Two pieces four feet long will be used for the sidewalk steps; three pieces 40 inches long will be needed for the garage steps; one piece eight feet long will be used to form the entry step on the front porch. The totals would be as follows:
2 pcs. 2 in. × 8 in. × 48 in. = 96 in.
3 pcs. 2 in. × 8 in. × 40 in. = 120 in.
1 pcs. 2 in. × 8 in. × 96 in. = 96 in.
Total = 312 in. or 26 ft.
Porch Edge Forms
The porch edge forms will be constructed out of 2 × 10 material. Enough material will need to be purchased to form the three exposed edges of the porch. Figure 8-104 shows a plan view of the porch with two porch ends at 6 feet, 4½ inches and one porch front at 11 feet, 3 inches. Each porch edge should be made out of a single piece of lumber, and each piece should be rounded up to the nearest two-foot increment, which will result in the following:
2 pcs. 2 in. × 10 in. × 8 ft. = 16 ft.
1 pcs. 2 in. × 10 in. × 12 ft. = 12 ft.
Total = 16 ft. + 12 ft. = 38 ft.
Porch Bottom Forms
The porch in this project is a slab that is suspended over a storage room in the basement. This will require the porch bottom to be formed so that the porch can be placed. The bottom will be formed out of plywood that will be supported by a framework of bracing. After the porch is placed and had a chance to cure sufficiently, the porch formwork will be taken down leaving only a suspended concrete slab. Figure 8-102 shows an example of the porch bottom plywood form work that will be required. Figure 8-112 shows the layout for the pieces of plywood.
The dimensions of the inside of the porch bottom are five foot seven by nine foot eight. Multiplying the dimensions would result in the following calculation:
5 ft 7 in x 9 ft 8 in = 53.97 ft2
A standard four foot by eight-foot sheet of plywood is equal to 32 square feet. It will take close to two sheets of plywood for the porch form bottom.
The porch bottom forms will require extensive bracing to support it while the concrete cures. A framed floor will be installed below the plywood to support it with two-by-four floor joists every two feet on-center. The floor joist will be supported by temporary framed walls every two feet. The 5 foot, 7 inch width of this porch will require at least four framed walls two feet on-center. Material for the porch bottom bracing will be as follows:
Porch Bottom Joists: 6 pcs. 2″ × 4″ × 5′-7″ = 33′-6″
2 pcs. 2″ × 4″ × 9′-8″ = 19′-4″
Temporary Walls Plates: 8 pcs. 2″ × 4″ × 9′-8″ = 77′-4″
Temporary Wall Studs: 24 pcs. 2″ × 4″ × 8′ = 192′
Although all 322 feet will be used for the temporary form bracing, most of it will be able to be salvaged and reused in other parts of the projects. An estimate of five form uses will be used to calculate the bracing material similar to what was done when estimating footing formwork. The total will be divided by five to calculate the amount to purchase for the project.
322 ft. ÷ 5 = 64′-6″
Figure 8-113 shows a cutaway view of the porch formwork’s temporary bracing.
Completing The Concrete Step Labor Costs
The concrete step labor costs will be estimated using the steps-on-grade subsection of the residential section of the National Construction Estimator. NCE Figure 8-14 shows a screenshot of the National Construction Estimator.
The concrete steps are priced per cubic yard of concrete. The 2.48 total cubic yards of concrete in the header section will be used to estimate the quantity of concrete for a total cost of
2.48 yd.3 × $182.00 = $451.36
A foundation finish costs section can be included in your estimate for miscellaneous concrete items needed to complete the project.
The building code requires that all basement rooms with habitual space have a separate form of egress in the case of an emergency such as a fire. Basement rooms such as bedrooms, family rooms, recreation rooms, dens, exercise rooms, media rooms, and offices would typically be defined as habitual rooms. Often the defined form of egress for these rooms is a window. There are also specific requirements for size and location of windows that are defined as egress windows. The code requirements for an egress window are as follows:
- The bottom of the egress window opening can’t exceed 44″ from the finished floor.
- The minimum opening area of the egress window is 5.7 square feet.
- The minimum egress window opening height is 24″ high.
- The minimum egress window opening is 20″ wide.
In addition to the window egress requirements, there are egress requirements for a window well when the bottom of the window is below the finished grade. The requirements for an egress window well are as follows:
- Egress window wells are required where the bottom of the egress window is below ground level.
- The egress well must not interfere with the egress window fully opening.
- The distance from the egress window to the back of the egress well must be at least 36″.
- The minimum area of the egress well must be 9 square feet (width × projection).
Egress window wells that are deeper than 44 inches also have specific requirements that are as follows:
- Egress ladders and/or steps are required on window wells deeper than 44″ and must be permanently attached.
- An egress ladder or step may encroach into a well up to 6″.
- Steps and/or distance between rungs of the ladder can’t exceed 18″.
- The rungs of an egress ladder must be 12″ wide or greater and must project a minimum of 3″ away from the back wall but can’t exceed 6″ from the back of the wall.
If the egress window is to have a cover, the cover must be able to be operated by the average person without the aid of tools.
There are many options available for meeting the window well requirements for basement windows including galvanized or painted steel window wells, polyethylene plastic window wells, and site made window wells. Window well construction may be simply utilitarian in construction, or it may be more decorative and have molded in features, such as escape ladders and imitation brick or stone façade. Often, egress window wells are constructed of snap together pieces that allow window wells of varying depths to be installed using standard size pieces.
Figure 8-114 shows an example of several painted steel window wells that have been installed on a basement foundation window before the foundation had been backfilled.
Figure 8-115 shows a steel window well with an imitation stone façade. The window well also has an attached escape ladder.
Completing the Foundation Finish Costs
The foundation finish costs will be completed by simply counting and listing the window wells. Figure 8-116 shows a basement plan view and identifies three basement windows identified by type mark A.
Each of these windows is listed in the window schedule as a 4’0” x 4’0” window. The “Window Well 52" W x 36" P x 46" H” is placed into the materials section of the estimating template from the hardware database and the count of three is manually entered into the spreadsheet.
NCE Figure 8-17 shows the window well subsection of the National Construction Estimator with the window wells closest to the actual window well highlighted. The crew, labor hours, unit, and unit labor cost of $50.20 is placed in the estimating template and the total of three manually entered into the quantity cell of the estimating template. Estimate Example 8-7 shows the completed foundation finish subsection of the NCE.
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