This chapter will cover items that are estimated in the sitework phase of construction, including demolition, tree and brush removal, site layout material and labor, excavation, erosion and sediment control. The discussion will begin with estimating items that are typically completed before excavation, including demolition, tree and brush removal, and site layout.
There are many occasions in the construction process where demolition must take place before new construction can begin. Sometimes new buildings are built in a location where there are existing structures and the entire old structure must be torn down and the debris hauled away. On other occasions remodeling takes place of existing buildings, and the demolition must be of a selective nature where some parts are removed and others are left intact. In each case, the demolition process must be part of the estimate, and there are many factors to consider including the type of demolition process, the disposal of the waste, and the hazardous materials.
Type of Demolition Process
The type of demolition process used is based upon factors such as the structure type and the amount to be demolished, such as the entire building or just selective parts.
Whole Building Demolition
Whole building demolition is used when the entire building is to be razed to the ground, the waste removed, and a new structure built in its place. The actual demolition process depends largely on the building type. Large concrete and masonry buildings are often removed by imploding the entire structure. This is a very specialized field that requires the expertise of a specialist with high explosives. Buildings may be demolished by using more conventional means, such as using a trackhoe or other heavy equipment in the demolition process (Figure 7-1).
There are usually several different elements of a demolition estimate. The first is the demolition of the structure itself. Whether the building is destroyed using explosives or conventional means, the estimates are usually based upon the type of structure; whether it is steel, concrete, masonry, or wood; and the size of the structure. Common methods calculate quantities based upon the volume of the standing structure or the square footage of the floor area for each floor. These are straightforward calculations based upon the size of the structure. The total volume is usually priced per cubic foot and might have costs somewhere between 25 and 40 cents per cubic foot.
The demolition of the foundation, footings, and concrete floors usually would be in addition to the main structure and might be priced per square foot or lineal foot, depending upon the specific element and its construction. The type and amount of steel reinforcing in the concrete might also add significantly to the cost.
Finally, the disposal of the rubble will need to be accounted for. This can be a significant cost to the demolition process. Factors that can go into the disposal cost include dump disposal fees, the distance that it will need to be hauled, and the presence of hazardous waste.
Waste disposal fees at the dump, also known as tipping charges, can vary greatly from location to location. They could be as low as $30.00 per ton to over $120.00 per ton. The local dump or trash disposal company will need to be checked for the actual costs.
The waste on site can be managed in a number of ways, depending upon the volume that needs handling. It may be possible to have a smaller three cubic yard trash bin placed at the site that is emptied weekly by a waste disposal company. This would usually be handled with a monthly fee. Higher volumes up to 40 cubic yards can be handled with a roll off dumpster (Figure 7-2). This is a large container that is left at the site, and when it is filled, the disposal company retrieves the container, hauls it to the waste disposal site to be emptied, and returns it to the job if needed. The cost for this service is usually priced in two parts. The first is a hauling cost per load or trip costs for the company to pick up the full container, empty it, and return it if needed. This is usually a fixed cost, such as $250 per trip. The second is the disposal fee charged by the local dump, which is also priced per ton. The price can vary greatly depending upon the local fee structure. In addition, the weight of the load can vary greatly depending upon the material being disposed of.
Another element that can increase demolition costs is the possibility of hazardous waste. The two most common concerns for the building contractor are asbestos and lead. Both materials were commonly used in a wide variety of building materials in the past, and it is not uncommon to find a site contaminated by one, or both, of these materials. The removal and cleanup of the hazards can be a significant cost that will involve several features. The first is conducting a survey to determine the possibility and quantity of the contaminants. This will include taking samples and having the samples tested for contaminants. Next, a removal plan will need to be prepared. Then, the hazardous waste will need to be removed and properly disposed of by trained asbestos removal or lead abatement specialists. All of this can be a very costly undertaking.
Site layout is the process of locating the building on the site and marking out areas in preparation for excavating the footings and foundation. A site plan is usually included in the set of working drawings that shows the building’s location on the site. Important considerations when locating the building on the site include observing setbacks and easements, which are established by the applicable zoning ordinances and building codes. Typically, a zoning ordinance will include required setbacks or distances that the structure must be positioned away from the building lot boundaries. Zoning ordinances can include front, side, and back building setbacks, and the construction must not be placed in such a way as it encroaches upon these setbacks.
Property lines are usually determined by survey stakes that are placed when the building lot is platted. Once the survey stakes are located, the measurements are made and temporary stakes are placed to mark the location of important reference points (Figure 7-3).
A common method of establishing corners and other points in the building location is to use batter boards. Batter boards are small structures that are built outside of the boundaries of the building and consist of placing stakes into the ground with lengths of framing lumber between the stakes. They are typically placed outside the corner and intersection locations of the building’s perimeter. The corners of the building are marked with the batter boards and string is placed between them. The intersection of the string is marked as the corners of the building. After the corners and intersection are located using the string stretched between the batter boards, the corners are transferred to the ground using a plumb bob attached to a string. Stakes are then placed in the ground at the corner points (Figure 7-4). Measurements are made from the stakes, and the outside of the excavation is determined and marked on the ground using aerosol marking paints (Figure 7-5).
It is not practical to automate the quantity input of all materials in this subsection as some things such as the quantity of layout stakes or nails are bulk consumable items, or items where the relative cost is small in relation to the time and effort that it would require to count the quantity of each item. Still, these items must be placed in the estimate to make sure that they are accounted for in the overall construction cost and purchased so that they will be available on the job site when needed. For items such as this, quantities placed in the estimate are based more upon experience of past usage and rules of thumb.
As was previously taught, batter boards are small temporary frames that are constructed, set up, and leveled on the building site. From the batter boards, strings are stretched to represent the edges and corners of the building that is being constructed. Corner batter boards are L shaped and are made of a 2″× 6″ top board and four stakes as shown in Figure 7-6. Straight batter boards (Figure 7-7) are also used to mark out other building projections. Straight batter boards are made of a single top 2″× 6″ with two stakes.
Using the combination of L shaped and straight batter boards, several different configurations are possible to lay out this building. One configuration may or may not be better than any other, but the construction estimator should understand some possible layouts so that sufficient material is purchased for the batter boards on the project. Figure 7-9 shows a possible sample building layout for a small house.
In Figure 7-9, there are six corner batter boards and three straight batter boards. In this example, no batter boards are combined.
The minimum length of the side for a corner batter board is five feet because the batter board must extend out past any excavation onto undisturbed soil, and the excavation for the foundation must be a minimum of two feet past the building line. If the batter board length for the building in Figure 7-9 were five feet long on each side, the estimate for batter board and stake material would be:
|Corner Batter Boards
||6 corners × 2 pieces × 5 ft. = 60 ft.
|Straight Batter Boards
3 straight × 1 piece × 5 ft. = 15 ft.
Total Batter Board Material = 75 ft.
|Batter Board Stakes
6 corners × 4 stakes = 24 stakes
3 straight × 2 stakes = 6 stakes
30 Stakes at 24 stakes/bundle = 1.5 bundles
Adding a Waste Factor
A waste factor is a percentage of material over the actual calculated raw quantity of material needed to cover some unforeseen usage, such as material that is too warped or damaged to be used or was perhaps cut the wrong size by mistake. The actual percentage to be used as the waste factor for any given material is a judgment call based upon past experience and historical records.
Site Layout Labor
The site layout labor can be completed using data from the National Construction Estimator (NCE). Using the search function, the keyword “Foundation Layout” is searched, which brings up several possibilities. Clicking on the link brings up a page in the cost book. We will use “Layout,” “Foundation Layout,” and “Medium to Large Residence” as an example.
The NCE identifies five relevant factors in determining the cost for site layout which are
- Craft@Hrs B1@7.86
- Unit LS
- Material 73.70
- Labor 263.20
- Total 336.70
Craft@Hrs identifies both the crew and the number of man-hours needed to complete the project. This means that crew B1, which has one laborer and one carpenter, will need 7.86 man-hours to complete the layout of this building. This means that it will take the two men 3.93 work hours or approximately half a day to complete the building layout.
The unit identified is LS, which stands for lump sum, and is another way of saying a single price for the entire job. Identified by the NCE, the material cost for laying out the building is $73.20. That and the labor cost of $263.00 can be used in preparing the site layout labor cost estimate.
The excavation activities include clearing the site, removing topsoil, footing and foundation excavation, installing utilities to the structure, and rough site grading.
Clear and Grub
Clear and grub includes tree and brush removal and other activities to clear the site in preparation for excavation. The removal of brush and trees from a building lot is often needed before excavation can begin. These costs can vary greatly depending upon the type of work that is required. The estimate for this work generally falls into one of several categories. The first is tree and brush removal, or what is commonly known as clear and grub. This consists of removing the vegetation from the lot so that construction can begin. The cost for clear and grub is usually based upon a price per acre, with the price variation based upon the type of material that needs to be removed. Typically, estimators distinguish between light brush, heavy brush, and wooded lots. Lots covered in either light or heavy brush would typically be scraped with a bulldozer or backhoe blade. Usually, the cost is estimated on a square foot basis. The NCE prices clearing and grub for a lot on an acre basis. In some cases, the square footage to be cleared would need to be converted to an acre unit of measurement.
Tree removal can vary depending upon the size and quantity of trees that need to be removed. One or two trees are priced on an individual basis with the price being determined by the diameter of the trees being removed. The cost of removing the tree stump is an additional cost and will need to be calculated separately. Clearing the trees from heavily wooded lots is usually calculated on an acre basis using tree harvesting equipment. The individual elements of excavation include clearing the site in preparation for the excavation.
Figure 7-11 shows an area for tree removal and clear and grub. A single ten-inch tree and stump will need to be removed and an area around the excavation cleared of brush prior to excavation. The edges of the area are a little untidy with inconsistent dimensions. However, an average area could be calculated. This would be done by first finding the average length of each side. The back horizontal dimension is 92′-6 ½″, and the front horizontal dimension is 87′-7″. To calculate the average length, add the two dimensions together and divide by two as shown in the following example:
(92′ 6 ½″ + 87′-6″) ÷ 2
(92.54′ + 87.5′) ÷ 2
180.04 ÷ 2 = 90.02′
The left side vertical dimension is 93′- ½″, and the right side vertical dimension is 82′- 0″. To calculate the average length, add the two dimensions together and divide by two as shown in the following example:
(93′- ½″ + 82′-0″) ÷ 2
(93.04′ + 82′) ÷ 2
175.04′ ÷ 2 = 87.52′
The clear and grub area would then be calculated by the following:
90.02′ × 87.52′ = 7878.55 ft2
The square footage could then be converted to an acre measurement by dividing the total by 43,560, which is the amount of square footage in an acre.
7878.55 ft2 ÷ 43,560 acres/ft2 = 0.18 acres
NCE Figure 7-2 shows a sample page from the NCE for both clearing and grubbing the site and removal of trees and stumps.
After the site has been clear, the next step is to remove the topsoil prior to footing and foundation excavation. The topsoil is the upper layer of soil. It is usually composed of minerals, organic matter, water, and air. It is the soil that supports most plant life. It is common practice to remove the soil prior to excavation and save it for later use when grading and landscaping (Figure 7-12). If the topsoil is not removed and stored separately, it will most likely be contaminated by mixing it with rocks and other excavated material. The layer of topsoil is most likely a few inches to a few feet thick. The cost for stripping the topsoil is usually calculated by determining the area that needs to be cleared by the depth of excavation. The quantity is usually priced per cubic yard.
Figure 7-13 shows an area for topsoil removal. The dimensions for the removal are 68′- 4″ x 50′- 3″ at an 8″ depth. The eight-inch depth will need to be converted to a foot quantity by dividing by 12. The calculations for determining the quantity of topsoil are as follows:
68.33′ × 50.25′ × 0.66′ = 2289.17 ft3
The cubic foot quantity will need to be converted to a cubic yard quantity by dividing the total by 27. The calculation is as follows:
One other element that may need to be taken into consideration is if the excavated topsoil needs to be hauled away. The price for hauling the soil is usually priced per cubic yard with the cost increasing as the length of the haul gets longer.
NCE Figure 7-3 shows a sample page from the NCE for stripping topsoil using a 65 HP bulldozer. The topsoil removal cost is priced per cubic yard. In addition, the price for hauling away the topsoil is shown, which is also priced per cubic yard. The cost per cubic yard for hauling away the topsoil varies depending upon the size of the truck used and the distance of the haul. In this example, the topsoil will be stored onsite for later use in backfill and grading.
Three possible elements of the foundation excavation are the excavating for the footing and foundation, trenching for shallow footings and foundations, and backfilling the excavation once the foundation is placed.
Several factors need to be taken into consideration when determining the quantity of soil removed for the footing and foundation excavation. The four factors are the footprint of the building, the excavation outside of the footprint of the building, the depth of the excavation, and the topsoil already removed.
Footprint of the Building
The shape of the building determines the size, shape, and depth of excavation that is needed. Larger, more complex buildings will require bigger excavations.
Excavation Outside the Footprint of the Foundation
Most foundation excavations extend past the boundaries of the foundation because space is needed for the workers to form and strip the foundation formwork. Typically, foundation excavations extend a minimum of two feet outside of the formwork (Figure 7-14).
Depth of Excavation
The depth of the foundation and footing excavation is determined by a number of factors, the first being the type of construction. In some areas, basements are a common element in residential construction, and in some areas, they are not. One of the factors that is often considered when determining to include a basement is the frost depth for the area. In areas of colder climates, the ground frequently freezes in the winter and the building’s footings need to be deeper than the depth of the frost. In addition, different portions of the excavation can be at different depths to account for full/partial basements or garages. Figure 7-15 shows an excavation for a basement at half depth with four feet tall foundation walls and a shallow excavation for the garage footings. Two distinct piles of soil are also shown where the topsoil and regular soil are kept separate for later backfilling.
Topsoil Already Removed
The topsoil where the excavation is to take place is removed as a first step in excavating for the footings and foundation. The topsoil is removed and either stored onsite or hauled away. In either case, the quantity of topsoil will not need to be included in the footing and foundation excavation quantity.
Foundation excavations are usually calculated using a cubic yard measurement by taking into account the factors of the footprint of the building, excavation outside of the building footprint, depth of excavation, and the depth of topsoil already removed.
Trenching for Shallow Foundations
Some foundation excavation is accomplished by trenching. Trenching could be combined with more traditional bulk excavation for excavating shallow garage footings, such as in Figure 7-16. Trench excavation can be used for shallow foundation construction such as slab on grade or post tensioned concrete slab foundations. Figure 7-17 shows a post tensioned concrete slab where the slab is thickened at the edges by digging a shallow trench around the exterior of the building.
A sample foundation excavation is shown in Figure 7-18. The excavation will have two different depths—a shallow excavation where the garage is located and a deeper excavation for the basement area of the house. In addition, a broad area of topsoil will be removed before the foundation excavation.
The first step in calculating the foundation excavation is to determine the building footprint and the area outside of the building footprint. Figure 7-19 shows the excavation with the outline of the main building footprint and the garage footprint superimposed in the excavation. It is assumed that the excavation outside of the footprint will extend two feet outside of the building footprint.
Determining the Area of Excavation
The square footage of the main building depth is determined by calculating the area of two rectangles consisting of the main building, including the front porch area, and the area excavated outside of the building footprint. Figure 7-20 shows the total excavation dimensions.
The calculation for the main building depth area is
(36′-0″ × 40′-0″) + (6′-3″× 15′-0″)
36.0′ × 40.0′ = 1,440 ft2
6.25′ × 15.0′ = 93.75 ft2
1,440 ft2 + 93.75 ft2 = 1,533.75 ft.2
The calculation for the garage excavation area is
20′-4″ × 26′-0″
20.33′ × 26.0′ = 528.67 ft2
Determining the Depth of Excavation
The depth of excavation is determined by the amount of topsoil removed and the depth of the excavation required. Figure 7-21 shows the excavation depth of six feet eight inches from the original ground level. Eight inches of topsoil are removed first and then the main foundation is excavated to a level of six feet. The garage foundation will be excavated to a level of two feet below the topsoil excavation depth.
The calculations for determining main building excavation quantity is
1,533.75 ft2 × 6′ = 9,202.50 ft3
The calculations for determining the garage excavation is
528.67 ft2 × 2′ = 1,057.34 ft3
The total of the two areas added together and converted to cubic yards is
Backfilling Around Foundation
Once the foundation has been placed, the soil that was removed will need to be backfilled around the foundation to bring the level of soil back up to the grade level. One method of calculating the foundation backfill quantity is to subtract the amount of soil removed for the foundation excavation and then subtract the volume of the amount excavated. In some cases, additional soil is backfilled above the original level soil against the foundation and sloped away from the foundation to allow water to flow away from the building. Another advantage of this is that the excess soil removed from the foundation excavation will not need to be hauled away. Figure 7-22 shows a foundation that has been backfilled above the original grade and sloped away from the building. Topsoil will need to be placed above the fill material.
When the backfilled soil is placed, it will also need to be compacted to prevent it from settling after the building is completed. This is usually accomplished by replacing the soil in layers, called lifts, and then compacting each layer. The compacting could be done using machine mounted equipment or portable “jumping jack” type compactors.
Figure 7-23 shows the excavation with the footing and foundation completed, ready for backfilling. The area of excavation outside of the foundation will be backfilled up to the level of the existing soil. In addition, the inside of the garage will also be filled to a level for the garage floor. The backfill in this area will need to be compacted as it is being filled in order to avoid any settling of the dirt once the house is complete.
Figure 7-24 shows the backfill complete up to the level of the existing soil. Calculating this quantity of backfill will require determining the area of the complex shape around the excavation and multiplying the area by the depth of the excavation. As there are several different area shapes with differing depths, this could be somewhat of a complex calculation. One quick method that could be used to get a rough number is to subtract the volume the structure occupies with the volume of soil removed from the excavation. Using this method of backfilling, there will be excess soil that will need to be hauled off the job site, which will entail an additional cost.
Figure 7-25 shows another method of backfilling, which is to build up the soil level around the foundation and grade it so that it slopes away from the building. This has several advantages in that the foundation excavation will not need to be as deep, requiring less initial excavation, and all of the soil excavated can be utilized on the job site and will not need to be hauled away. In addition, a slope will be created that will allow water to naturally drain away from the building, helping to keep the foundation dry.
NCE Figure 7-4 shows a sample page from the NCE for excavation with heavy equipment. The foundation excavation could be priced using a backhoe with the ¾ CY bucket in average soils.
Estimating Utility Excavation and Installation
Estimating the installation of building utilities can be a complex process that involves many participants and gathering information from a wide variety of sources. Often this involves connections with a number of different public and private utilities, each with its own requirements and regulation. It is expected that the estimator will become familiar with the specific procedures that each utility requires. This is often referred to as “doing due diligence.”
Common utility installations could include the water and sewer service, electrical service, natural gas or propane supply, and communications infrastructure. Water, sewer, and gas infrastructure has traditionally been supplied with underground installation and electricity and communication via overhead transmission lines. Some construction may require traditional overhead installation, but most modern infrastructure is delivered underground and will require some form of trenching.
Utility Trench Size
The width and depth of the trench requirements can vary greatly by the local conditions and utility requirements. Most installations would involve a minimal depth requirement for health and safety reasons, but other factors can also come into play. For example, the depth of the sewer line would be determined by the depth of the public sewer or private septic tank. Some sewer line installations are deep enough that they would allow the sewer line to be excavated below the bottom of basement footing and would allow the natural drainage of the building sewer. Other installations could be shallower, which would require basement installations to use a sewage pump to move the effulgent up to a level above the utility sewer level to provide for the natural drainage of the line. This would mean a shallower excavation.
The depth of the water line excavation could change based upon local requirements. Water lines need to be installed below the frost depth, which could vary from location to location. Other utilities such as electricity, gas, and communication have minimum and maximum depth requirements. In the case of electricity, gas, and communication lines, it is common to allow lines that are run in conduit to be placed at a shallower depth than direct burial type of lines.
Several factors also must be taken into account when determining the width of a utility trench. Laborers need sufficient workspace to safely install the utility. Often, the deeper the trench, the wider it will need to be for work to be performed in a safe manner. Deeper trenches often also require either a slope-sided excavation or shoring to prevent the sides of the trench from collapsing onto the workers.
In some instances, several utilities can be installed in the same trench, but there are usually requirements for the lines to be separated by specific distances, which can require a wider excavation. For example, water and sewer lines can be allowed in the same trench, however, there may specific requirements to do so, such as requiring the water and sewer lines to be a minimum of one foot apart horizontally and the sewer line to be located a minimum of one foot below the water line. On occasion, electricity, gas, and communication lines can be allowed in the same trench, however, there would be specific separation requirements requiring additional trench width. Electricity, gas, and communication are usually not allowed to be located in the same trench as water and sewer lines.
The length of the excavation is determined by the distance between the utility connection and where it enters the structure. In some cases, a developed lot would have connections run to the property and the connections could be made by simply tying into the systems. In other cases, the utility connection will need to extend into the street and may require tearing up and replacing a portion of the street.
Underground utility lines need to be supported continually along their length. For example, sewer lines need to be installed on a support bed that consistently slopes. They also need to be installed on the required grade to allow the sewage to flow by gravity away from the structure. Unnecessary depressions and bumps in the excavation can hinder the flow of the system and cause future problems. It is common to install utility lines on engineered fill material, such as sand, to allow the consistent grading of the line bed. In addition, sand can be used to surround the utility line to protect it from damage by rocks and other debris that could come into contact with the line as it is backfilled. The sand bed provides other advantages, including providing an indicator of the location of the utility should a need arise in the future to excavate the utility.
Requirements for bedding sand vary from circumstance to circumstance. Sand bedding may be required for direct burial lines such as electrical, gas, and communication lines, but it may be omitted in lines that are run in conduit.
Sand that is placed below the utility line is called bedding sand, and sand that is placed above the utility line is shading sand. Additional sand is often needed to make up the space between the bedding sand and the shading sand to the thickness of the utility line. For example, if the requirements were for a four-inch layer of bedding sand and a six-inch layer of shading sand in a trench that contained a four-inch diameter sewer line, the sand requirement would be a total sand depth of 14 inches.
4″ Bedding Sand + 4″ Pipe Thickness + 6″ Shading Sand = 14″ Total Sand Depth
Figure 7-26 shows an example of a main sewer line that has been installed in a bed of sand.
Estimating Sewer Connection
The sewer connection is the cost associated with the excavation and installation of the sewer line from the public utility to the house. The cost would include the excavation of the trench, the installation of the sewer pipe and cleanouts, and the backfilling of the trench.
Figure 7-27 shows a PVC pipe sewer line installed in a trench. The soil in the bottom of the trench is fairly free of large rocks or other debris and has been graded to a consistent slope, and sand has not been placed in the bed.
Sewer Line Cost
NCE Figure 7-5 shows the NCE cost for sewer line installation. Installation is priced as a lump sum subcontract cost based on the type of sewer pipe installed. Different costs are also shown if the line is run to the street in the front of the structure or to an alley in the back. The lump sum price includes up to 40 feet of installation with an additional charge per lineal foot over the 40-foot standard.
Figure 7-28 shows a four-inch PVC sewer line run to the front of the house. The excavation will run for a distance of 34 feet. This falls within the allotted 40 feet base run price estimate, so the lump sum rate of $2,200.00 will apply.
Estimating Sand Fill
In this estimate example, the contractor will provide a bulk supply of sand material to be used as bedding for the sewer pipe and the rest of the utility lines (Figure 7-29). The approximate amount of sand needed for the project will need to be calculated. The quantity of sand for the sewer line is determined by the length of the trench, the width of the trench, and the depth of the sand. The sand will be placed 6″ above and 6″ below the pipe. With a 4″ diameter sewer pipe, the total sand depth is 16″ (Figure 7-30).
The calculations for determining the quantity of fill sand is as follows:
24″ × 16″ × 34′
2′ × 1.33′ × 34′
The water connection is the cost associated with the cost of excavation and installation of the water line from the public utility to the house. The installation is handled on a subcontractor basis. The cost includes the excavation of the trench, the installation of the water line, water meter, and backflow preventer. Code requires that the water line is installed at least twelve inches away from and twelve inches above the sewer line. It also requires it to be below the frost line. Figure 7-32 shows a trench excavation and water meter box in preparation for the installation of a water line.
Figure 7-31 shows a separate 34-foot trench excavation in the front of the house for the water line. The trench will be 12 inches wide.
The one-inch water line will be installed on a bed of sand six inches above and below (Figure 7-32).
NCE Figure 7-6 shows the water meter installation costs from the NCE. The description of the cost explains that this is a lump sum cost for the excavation and installation of the water service, including the parts and materials needed. Cost would be less if building on a build-ready lot where the main utility services were already installed and the contractor simply needed to hook up to the existing system. The cost for the installation of the backflow preventer, which will prevent any contaminated water from entering the city’s portable water system, is also priced as an additional cost.
Estimating the Electrical Supply
The electrical installation in most situations is provided by the electrical utility. Electricity was traditionally supplied to the residence by above ground utility poles and an overhead electrical service line. This may still be the case in many circumstances, particularly if the building is a long existing development. However, most modern installations are supplied by an underground service. Most electrical power is delivered along high voltage power lines and must be stepped down to the standard 100 to 120 volt, 60 hertz standard that is common in the United States before being delivered to the customer. A transformer is commonly located on, or close to, the property to provide the change in electrical voltage. The transformer can be a utility pole mounted system or a ground mounted system. As a rule, the electrical utility is responsible for the installation and maintenance of the electrical service across the owner’s property, from the utility’s supply equipment to the individual electrical meter.
Figure 7-33 shows an example of an underground electrical service installation. The contractor is responsible for excavating a trench from the transformer to the electrical meter base panel. A small framed power wall has been installed to attach the meter base. After the trench is dug, the power wall framed, the meter base, and conduit put in place, the power company’s service crew installs the main power line from the transformer to the meter base
Once all of this has been completed and an inspection made by the local building official, the trench will be backfilled, compacted, and the meter will be set by the power company. This will provide power for the building of the house and will ultimately become the power supply for the finished structure.
Figure 7-34 shows the underground electrical supply installation from a previously installed transformer to the meter base location on the back of the garage wall. The power line will be installed in a two-inch diameter PVC electrical conduit buried in a 12-inch-wide by 30-inch-deep trench that is 41 feet long. The electrical supply estimate in this section will include installing the electrical supply lines and excavating, backfilling, and compacting the trench. In addition, the contractor will supply a quantity of sand fill for backfilling around the supply conduit.
Estimating Electrical Supply Installation
The cost for estimating the installation of the electrical supply lines by the power utility will need to be obtained from the company. Sometimes this can be done by using an online installation cost estimator provided by the power company, such as the one provided on Rocky Mountain Power’s website.
To begin using the estimator, click the Line Extension Estimator → Get Started buttons. Select the state from the drop-down list and put the distance of the installation of 41 feet that was calculated from the plans and press the Next button (Figure 7-35).
The next screen has seven different options for installing the power line. In this case, the transformer has been installed on the site and the power will be run underground from the transformer to the meter base in a contractor supplied trench and conduit. Pick the Short Underground from Underground option and click the Next button (Figure 7-36).
Click the Yes radio button to indicate that the ground level transformer is already installed and then click the Get a Ballpark Estimate button to get the cost estimate (Figure 7-37).
The price estimate of $600 is what can be put into the estimating template as the electrical supply installation cost.
Estimating Electrical Trench Excavation
The contractor is responsible for the trench excavation for the power supply line trench. The depth of the trench is determined by the type of installation and the power company requirements. The power company has provided the diagram shown in Figure 7-38 for the electrical trench excavation.
The length of the excavation is determined by finding the length from the transformer to the meter base. Trench excavation is priced in the NCE as a lineal foot cost based upon the width of the trench and the type of soil. The electrical supply example in Figure 6-84 identifies the trench as being 12 inches wide x 30-inch-deep x 41 feet long. The excavation cost of $2.04 per lineal foot for medium soil from the NCE will be used for this estimate (Figure 6-89). The cost is calculated as follows:
41' x $2.04 per LF = $83.64
Estimating Trench Backfill, Compaction, and Sand Fill
Trench backfill and compaction are priced in the NCE as a cubic yard cost. The quantity of soil to be backfilled and compacted is determined by the following:
12″ × 30″ × 41′
1' x 2.5' x 41' = 102.5 ft3
The NCE estimates the price of backfill using a front-end loader 60 hp as $2.32 per cubic yard (Figure 6-89). The cost for backfill would be
$2.19 x 3.80 yd3 = $8.32
The NCE estimates the price of compaction using a “jumping jack” type compactor as $3.95 per cubic yard (Figure 6-89). The cost for compaction would be
$4.10 x 3.80 yd3 = $15.58
Estimating Sand Fill
The power company has specific requirements for the type of backfill that is required around the conduit or power cable. In order to avoid the possibility that the soil on site doesn’t meet the requirements, sand will be provided by the contractor. Four inches of bedding sand, six inches of cover sand, and two inches of sand for the diameter of the pipe for a total depth of 12 inches will be used. The calculations for determining the quantity of fill sand would be as follows:
12" x 12" x 41'
1' x 1' x 41' = 41 ft3
The NCE prices the equipment and labor for installation for the sand bedding at $1.42 per cubic yard. The calculation would be
1.52 yd3 x $1.29 = $1.97
NCE Figure 7-7 shows the trenching, backfill, and sand fill cost for the electrical trench.
Estimating the Gas Supply
Residential construction is often able to take advantage of either natural gas or propane for use in heating and cooking. The installation cost will be different for the two types of fuel. Propane is usually supplied by a storage tank that is placed upon the property. The storage tank could be rented or purchased. A line is run underground from the storage tank to the building to supply the gas appliances. Costs to install propane would include the tank, excavation, and supply lines from the tank to the building.
Natural gas is usually run from underground utility lines that are installed by the gas company. The gas is supplied to the property under high pressure to a gas meter that reduces the pressure and measures the amount of gas used, so the gas utility can bill the customer. The site work phase cost for natural gas would include excavation of a trench for the installation of the gas supply, sand bedding for the gas line, backfill, and compaction of the trench.
Figure 7-39 shows the rough installation for a natural gas supply meter. The contractor is responsible for excavating a trench and providing bedding sand for the gas utility line. In some installations, the customer is responsible for proving a conduit for the gas line. Other installations may not require a conduit but could require sand bedding and shading. The contractor also installs the interior gas supply piping and tests it for leaks before the gas meter is installed.
Once all of the infrastructure is in place, tested, and inspected, the gas utility will install the meter to supply the gas to the house.
Estimating Gas Supply Trenching
Figure 7-40 shows an example of the gas supply trench that is 12 inches wide, 30 inches deep, and 40 feet long. The excavation cost of $2.05 per lineal foot for medium soil from the NCE will be used for this estimate, the same as was used for the electrical trench (NCE Figure 7-7). The cost is calculated as follows:
40' x $2.05 per LF = $82.00
Estimating Trench Backfill, Compaction, and Sand Fill
Trench backfill and compaction are priced in the NCE as a cubic yard cost. The quantity of soil to be backfilled and compacted is determined by the following:
12″ × 30″ × 40′
1' x 2.5' x 40' = 100 ft3
The NCE estimates the price of backfill using a front-end loader 60 hp as $2.19 per cubic yard (NCE Figure 7-7). The cost for backfill would be
$2.19 x 3.70 yd3 = $8.10
The NCE estimates the price of compaction using a “jumping jack” type compactor as $4.10 per cubic yard (Figure 6-89). The cost for compaction would be
$4.10 x 3.70 yd3 = $14.62
Estimating Sand Fill
The gas company has specific requirements for the type of backfill that is required around the gas line. To avoid the possibility that the soil on site does not meet the requirements, the contractor will provide the sand. Four inches of bedding sand, six inches cover sand, and two inches of sand for the diameter of the pipe for a total depth of 12 inches will be used. The calculations for determining the quantity of fill sand would be as follows:
12" x 12" x 40'
1' x 1' x 40' = 40 ft3
The NCE prices the equipment and labor for installation for the sand bedding at $1.42 per cubic yard. The calculation would be
1.48 yd3 x $1.29 = $1.91
Rough Grading Estimate
The rough grading cost includes the cost for spreading the previously excavated topsoil over the backfilled soil excavation. Figure 7-41 shows an example where the topsoil has been graded over the backfill.
The topsoil that was removed prior to foundation excavation and stored on the site will be used for the rough grading.
There will not be any topsoil fill underneath the driveway area as that will have compacted engineered fill material for supporting the driveway. NCE Figure 7-8 shows the NCE cost to spread the topsoil using a 65 hp dozer and places the cost at $1.01 per cubic yard.
Using the quantity of 103.3 cubic yards that was previously calculated to strip the topsoil before foundation excavation, the cost for rough grading would be
103.3 yd3 x $1.01 = $104.33
Estimating Erosion and Sediment Control
Stormwater runoff from construction sites can be a significant source of water pollution. When soil is excavated and plant material removed in any of the previously discussed excavation activities, the water that runs across the bare soil picks up silts and other pollutants, which then makes its way into streams and other waterways. The Environmental Protection Agency has regulations that oversee the management of stormwater pollution on construction sites. Excavation activities that impact one acre or larger sites are required to submit a stormwater pollution and prevention plan, commonly referred to as a SWPPP’s plan, before excavation activities can begin. The purpose of the SWPPP’s plan is to outline the methods that will be used on a construction site to control the silt and other pollutants from stormwater runoff.
Some examples of elements in a stormwater plan would be erecting a silt fence, using straw bales in drainage ditches, and covering the ground with erosion control mats.
Silt fences are fences made of some form of semi-porous geotextile fabric. Stakes are attached to the fabric at regular intervals. The fence is placed on the downside of a sloped lot, and the bottom of the fence is buried in a shallow trench approximately six inches deep. The semi-porous nature of the fence allows water to flow through the fence while trapping the silt particles behind the fence. Figure 7-43 shows an example of a silt fence.
Silt fence material is commonly purchased in rolls such as 100 feet long and three feet high. Installation costs are estimated as a lineal foot cost and would include shallow trench excavation and installing the fence. Figure 7-44 shows the installation of 136 feet of silt fence along the rear and side of the property.
NCE Figure 7-9 shows the installation price of the silt fence in the NCE.
Craftsman Book Company. (n.d.). 2018 Craftsman Costbooks. Retrieved from https://www.craftsman-book.com/
Richard Pray Craftsman Book Company, 2018 National Construction Estimator, 66 Edition.