Part 11

Before fixing the price for excavation, it is advisable to investigate the character of the soil by making boring tests. Where there is rock to be blasted in making the excavation, a special price should be given in the estimate. If the ground is wet, rendering pumping necessary, provision should be made for the cost of the extra labor needed. The disposition to be made of the excavated material should also be considered; if it must be hauled a long distance, the cost will be much greater than if the soil can be _wasted_ near by. To aid in estimating the actual cost, it is convenient and approximately correct to consider 1 cubic yard of ordinary earth as a load for an ordinary two-horse wagon.

In making calculations of the amount of material to be removed, care should be taken to note the existing levels of the ground and those required by the drawings. The excavation should be figured (and made) at least 1 foot greater than the size of the foundation, so as to provide room for setting the masonry, pointing, etc.

Excavation for pipes, drains, etc. should be at least 9 inches wider than the diameter of the pipe to be laid therein. If the soil in which the excavation is to be made is of a loose and sandy nature that is liable to crumble and slide, a slope, say of 3 inches horizontal to 1 foot vertical, should be allowed on both sides of the trenches. If the latter are of considerable depth, it is sometimes necessary to curb or shore up the sides, in which case an allowance should be made in the estimate for the lumber required. If piles are required, they should be figured at so much per linear foot, driven.

ACTUAL COST OF EXCAVATION

=8.= In order that an idea may be formed of the actual cost of excavating various kinds of soils, figures based on work actually performed are here given. On this work, for a day of 8 hours, a laborer was paid $2, and a driver with a two-horse team, $4.

As a rule, one laborer can excavate about 7 cubic yards of sandy soil in 8 hours. Thus, at the rate of 25 cents per hour, the cost of excavating this kind of soil is about 28½ cents per cubic yard, provided the material is wasted around the building. To this figure, however, must be added 4 or 5 cents to cover the foreman’s wages, the exact amount depending on the number of men under the foreman. This brings the total cost per cubic yard to about 33 cents.

When the material has to be carted away, the cost is further increased. A team with a driver can haul away about 20 cubic yards of soil in a day if the haul is only about ½ mile. In order to do this, however, an extra wagon must be at hand so that the laborers can be loading one wagon while the team is hauling away the other. Thus, the cost of hauling 1 cubic yard of excavated material ½ mile is 20 cents. The total cost, therefore, of excavating 1 cubic yard of sandy soil and hauling it ½ mile is 33 + 20 = 53 cents.

=9.= If the soil is compact gravel, the cost of excavating, including the foreman’s time, will be from 34 to 65 cents per cubic yard, depending on its hardness. It costs about the same to haul compact gravel as it does to haul sandy soil.

The exact cost of excavating wet soil cannot be given, as the conditions encountered may vary in each case. In a stated time, a laborer will excavate nearly as much wet material as dry material, but the conditions of sheet piling and pumping out water makes the price uncertain.

Such excavation is usually carried on at a cost of from 75 cents to $1.25 per cubic yard.

In excavating rock, three men—one rockman and two laborers—usually work together. For a day of 8 hours, the rockman receives $3 and each laborer gets $2. Together, therefore, the wages of the three amounts to $7 a day. These men will excavate about 6 cubic yards of rock in 1 day, making the rock excavation cost $1.17 per cubic yard. To this must be added the cost of explosives, which is about 10 cents per cubic yard, and the wear on tools. This latter expense can hardly be estimated, but may also be considered as 10 cents per cubic yard, thus bringing the total cost of rock excavation up to $1.37 per cubic yard for rock wasted at the building.

=10.= To sum up, excavation in sandy soil wasted around the building costs 33 cents per cubic yard; if hauled ½ mile, it costs 53 cents per cubic yard. If the soil is compact gravel and is wasted around the building, excavation costs from 34 to 65 cents per cubic yard; if hauled ½ mile, from 54 to 85 cents per cubic yard. Wet excavation with no piling or pumping costs about the same as dry; with piling and pumping, it costs from 75 cents to $1.25 per cubic yard. Rock work costs $1.37 per cubic yard if wasted around the building. These figures do not include the contractor’s profit.

CONTRACTOR’S METHOD OF FIGURING EXCAVATION

=11.= Besides the actual cost of excavation, the contractor, in estimating, must include such items as office expenses, builder’s profits, etc. The following method of figuring, which is employed by the estimator of a large contracting firm in the eastern part of the United States, will therefore be found useful. As in the preceding case, the prices will be found to vary in different localities; therefore, the figures given should only be used as a guide in estimating.

The prices are based on labor at $2 per day of 8 hours and a two-horse team and driver at $5 per day of 8 hours. The excavation is assumed to be made in ground varying from made ground to a moderately stiff clay. The prices do not include the cost of shoring or pumping, and are based on the assumption that there is no frost of any account while operations are being carried out. Four classes of excavation are recognized:

1. Excavation in trenches up to 5 feet deep, excavated material spread on site about trenches, including back filling around walls, costs from 40 to 50 cents per cubic yard.

2. Trenches from 5 to 10 feet deep, excavated material spread on site adjacent to trenches, including back filling around walls, costs from 65 to 75 cents per cubic yard.

3. For cellars, or similar digging, up to 6 feet deep and having an area large enough to use a plow for loosening the earth (say areas 50 ft. × 20 ft. and over), excavated material being spread on site adjacent to work, costs from 33 to 38 cents per cubic yard if a scoop can be used, and from 40 to 45 cents per cubic yard if the material must be loaded on a wagon to haul it out of the excavation.

4. When the conditions are the same as those just given, except that the excavation is from 6 to 10 feet deep, the price is about 45 cents per cubic yard.

The prices just given do not include hauling, except short hauls immediately in the vicinity of the operations. The cost of hauling will depend on the distance to the place where the material is to be dumped.

=12.= To obtain the cost of any of the classes of excavation just given, including hauling, divide the hire of the team per day by the number of cubic yards that can be removed to the dumping place per day, and increase the preceding prices by that amount.

To figure the cost of sheet piling, measure the area to be sheet-piled and allow for such stringers and braces as judgment may suggest. Since the lumber may be used for other purposes after serving as piling, its value should be estimated at 75 per cent. of the market price. It usually costs about $7 per thousand feet to put the piling in place. As a rule, 3" × 10" planks are used for this purpose.

The foregoing prices cover the general run of building work. For large office buildings and other structures of a similar nature, where it is necessary to excavate to a depth of about 25 feet and where several varieties of ground are likely to be encountered, an average price for digging (exclusive of pumping or shoring, but including a haul not exceeding 1 mile) is $1.25 per cubic yard. If large boulders are likely to be encountered in excavating, the price should be at least $1.50 per cubic yard.

DITCH WORK

=13.= In estimating the cost of =ditch work=, there are several factors that influence the price. A narrow ditch costs more to dig per cubic yard than a wide one; likewise, a deep ditch costs more than a shallow one. Following are given prices for laying agricultural drain tiling. While these figures do not include builder’s profit, they are based on the actual cost of work, the wages for a day of 8 hours being $2 for laborers, $2.50 for the foreman, and $4 for a horse and driver. In sections of the country where higher wages are paid, it will be necessary to increase the figures at a proportional rate when making estimates.

For trenches 3 feet deep and 18 inches wide, in very hard, clay soil with about 10 inches of loam on top, the cost of excavating is about 12 cents per linear foot, or 72 cents per cubic yard. For filling in the trench with the aid of a team and a scraper, it costs ¾ cent per linear foot. For laying a 4-inch tile, including distributing along the trench, the cost is ¾ cent per linear foot. For picking stones off of the ground and placing them over the pipe to a depth of about 8 inches, it costs 2¼ cents per linear foot. Each outlet built of field stones laid in cement costs from $5 to $8.

CALCULATING THE VOLUME OF AN EXCAVATION

=14.= The ordinary rules of mensuration are all that are needed to compute the =volume= of any excavation. The work is very simple when the area to be removed is regular; but when the outlines are very irregular and broken, the easiest method to employ in calculating the excavation is to divide the plan into geometrical figures that are easy to compute, and then calculate the area of each one separately. Adding these areas and multiplying their sum by the depth of the cellar will give the volume of the excavation.

This method will be made clear by referring to Fig. 1, which represents the plan of an irregular foundation. To compute the area of the excavation, the plan is divided into the rectangles _a d c b_, _l k b m, j i h g, g f e c_, and the polygons _n q p o, t u r s_, and _a x w v_. By scaling on the drawing the dimensions of these figures, the area of each may then be readily determined by calculation.

=15.= It is sometimes necessary to find the volume of an excavation, the surface of which is very irregular, as in Fig. 2. In such a case, the following method may be used: Divide the surface of the excavation into a number of squares, or rectangles, as at _d e f c_; these represent the ends of prisms, the other ends of which are the bottom of the excavation, as at _a h g b_. Then calculate the volume of each prism by ascertaining the height of the four corners above the bottom; add these measurements together, divide the sum by 4 (the number of corners), and multiply the result by the end area, as _a h g b_; the product will be the volume of the prism. The sum of these partial volumes will be an accurate estimate of the contents of the excavation.

CONCRETE WORK

=16. Plain concrete work= is usually paid for by the cubic yard. The contractor furnishes all material, including the lumber, to make the forms; he also erects the forms and removes them after the concrete has been placed. There is no fixed practice regarding openings in walls. Usually, small openings under, say, 100 square feet in superficial area are considered as solid. All larger openings are deducted from the work when measuring for payment. In some localities, the actual volume of the concrete work is taken by the contractor as a basis of the cost. In either case, it is of prime importance that the architect and the contractor make some distinct agreement _beforehand_ as to exactly how the concrete work is to be measured and paid for.

=Reinforced-concrete work= is also often measured by the cubic yard, although sometimes it is contracted for as a finished building. The steel reinforcement is sometimes included in the price. Often, patented steel reinforcement is bought separately and delivered to the contractor; at other times, the contractor buys the patented steel or else makes it and pays a royalty to the holder of the patent. Reinforced-concrete floors are sometimes measured by the cubic yard and sometimes by the square yard, according to agreement. Pavements are usually measured by the square foot or by the square yard.

In Table II are given the costs of stone concrete and gravel concrete. These figures do not include builder’s profit, cost of superintendence, or cost of forms. They are based on the following costs: Labor, 25 cents per hour; cement, $2 per barrel; sand, $1.50 per cubic yard; crushed stone, $1.65 per cubic yard; gravel, $1 per cubic yard.

To the values given in the table, the price of the wooden forms, both for material and erection, must be added. This of course varies considerably, according to whether the work is straight or has a number of corners and openings in it.

TABLE II

COST OF PLAIN STONE CONCRETE ===================+===================+=============================== Mixture | Quantity | Cost ------+-----+------+------+-----+------+------+-----+------+-----+----- Cement|Sand |Broken|Cement|Sand |Broken|Cement|Sand |Broken|Labor|Total Parts|Parts| Stone| Bar- |Cubic| Stone| | | Stone| | | | Parts| rels |Yards| Cubic| | | | | | | | | | Yards| | | | | ------+-----+------+------+-----+------+------+-----+------+-----+----- 1 | 2 | 4 | 1.5 | .45 | .90 |$3.00 |$.68 |$1.49 |$.75 |$5.92 1 | 3 | 5 | 1.1 | .50 | .85 | 2.20 | .75 | 1.40 | .75 | 5.10 1 | 3 | 6 | 1.0 | .45 | .90 | 2.00 | .68 | 1.49 | .75 | 4.92 ------+-----+------+------+-----+------+------+-----+------+-----+-----

COST OF PLAIN GRAVEL CONCRETE -------------------+-------------------+------------------------------ Mixture | Quantity | Cost ------+-----+------+------+-----+------+------+----+------+-----+----- Cement|Sand |Gravel|Cement|Sand |Gravel|Cement|Sand|Gravel|Labor|Total Parts|Parts|Parts | Bar- |Cubic|Cubic | | | | | | | | rels |Yards|Yards | | | | | ------+-----+------+------+-----+------+------+----+------+-----+----- 1 | 2 | 4 | 1.3 | .4 | .80 |$2.60 |$.60|$ .80 |$.75 |$4.75 1 | 3 | 5 | 1.0 | .5 | .80 | 2.00 | .75| .80 | .75 | 4.30 1 | 3 | 6 | .9 | .4 | .85 | 1.80 | .60| .85 | .75 | 4.00 ======+=====+======+======+=====+======+======+====+======+=====+=====

The price of forms, including both material and erection, may be said to vary from 50 cents for ordinary cellar work to $2 for heavy retaining walls per cubic yard of concrete placed.

DATA ON REINFORCED-CONCRETE BUILDING

=17.= The cost of =reinforced-concrete buildings= varies with the market price of cement and the steel bars or metal used for reinforcing. At present, reinforced-concrete buildings of the factory type constructed of common, hard, stretcher-brick walls and reinforced-concrete floors, roof, and columns with foundations may be built for from $1.35 to $1.65 per square foot of floor area. Usually, the height of ceilings in factory buildings is about 14 feet from floor to floor, thus making the cost of this type of building approximately from 10 to 12 cents per cubic foot. For buildings of a better commercial type, with face-brick walls and terra-cotta trimmings, the cost per square foot of floor area will range from $1.65 to $1.90, making the cost per cubic foot from 12 to 14 cents.

Reinforced-concrete buildings, as a rule, exceed the cost of buildings of slow-burning construction of the same size by an amount about equal to the cost of the metallic reinforcement. In other words, a building of reinforced concrete costs from 10 to 25 per cent. more than the same building of slow-burning construction.

The price of reinforced concrete per cubic yard varies within wide limits, depending on the mass of concrete employed and the intricacies of the forms. In building construction, reinforced concrete, including the price of the forms, can usually be placed for from $12 to $18 per cubic yard, the cost of the steel reinforcement being added.

Where the building is of considerable height, the same forms used in the three lower stories may be used in constructing the balance of the building. In such a case, the cost of the forms will probably not exceed $6 for each cubic yard of concrete placed. If the building is only two or three stories in height, and the work is rushed by using new centering in each floor, the cost of the forms will range from $7 to $9 per cubic yard of concrete.

The cost of form work for floor construction will range from 10 to 12 cents per square foot. Column forms will cost in the neighborhood of 20 or 25 cents per running foot. The forms used for fine concrete-wall construction require considerable time and bracing, and generally must be executed with great care where finished work is required. Such forms will cost from 8 to 10 cents per square foot of form on both sides of the wall, but will greatly exceed this price if molded courses or paneled spandrels are to be formed and lettering is to be cut in the work.

=18.= In estimating the cost of =reinforced-concrete slabs=, the cost of the centering, the concrete, and the steel reinforcements must be considered. The cost of centering for slab work varies from 5 to 7 cents per square foot, the latter figure probably being more nearly correct for usual conditions. The concrete for plain reinforced-concrete slab construction on steel beams can be placed for about $5.60 per cubic yard, or 1¾ cents for a square foot 1 inch in thickness. At present market values, the steel for reinforcing slabs can usually be considered as costing about 3 cents a pound, the pound price increasing as the rods decrease in size.

Table III gives the approximate cost, in cents per square foot, of constructing different thicknesses of reinforced-concrete slabs on steel-beam construction with the different sizes of reinforcing bars usually employed. The prices include cost of centering, concrete, and steel reinforcement.

=19.= Table III cannot be used for estimating the cost of a reinforced-concrete floor with reinforced-concrete beams and girders. In the construction of such a floor, the centering is much more costly than where steel beams are used for the support of the floor slab. On an average, the centering for the reinforced-concrete floor systems, including the studding and shoring, will cost from 20 to 22 cents per square foot, the sides of the beam and girder forms being included in the square-foot estimate. This cost is materially reduced where the centering is used over and over again for the construction of upper floors, so that where the building is six or eight stories in height, the average cost of the centering will not exceed 10 or 12 cents per square foot, including shoring, as just mentioned. Owing to the difficulty encountered in placing the concrete in the beams, the tamping required with slice bars, etc., and the expense of placing the reinforcement, the concrete for such construction will cost about $7.50 or $8 per cubic yard. The steel for the entire construction will usually average from 3 to 4 cents a pound, depending on whether plain rods or deformed bars are used, or whether the system is made up of loose rods or fabricated frames. In estimating the cost of such a floor system, the centering should be figured by a carefully itemized estimate, or roughly from the preceding figures. The amount of concrete in both the slab beams and columns should be estimated, and the total number of cubic yards required for the entire work should be determined; then the unit price for providing and placing the concrete should be carefully considered with reference to local conditions of labor and cost of material.

TABLE III

COST IN CENTS PER SQUARE FOOT OF REINFORCED- CONCRETE FLOOR SLABS SUPPORTED ON STEEL BEAMS =========+=========+========+=========+========+======== Thickness|⁵/₁₆-Inch| ⅜-Inch |⁷/₁₆-Inch | ½-Inch |⅝-Inch of Slab |Diameter |Diameter|Diameter |Diameter|Diameter Inches | Rods at |Rods at | Rods at |Rods at |Rods at | 6-Inch | 6-Inch | 6-Inch | 6-Inch | 6-Inch | Centers |Centers | Centers |Centers |Centers ---------+---------+--------+---------+--------+-------- 3½ | 14.87 | 15.58 | | | 4 | 15.75 | 16.46 | 17.24 | | 4½ | 16.62 | 17.33 | 18.11 | 18.87 | 5 | 17.50 | 18.21 | 19.00 | 19.75 | 20.87 5½ | 18.37 | 19.08 | 19.87 | 20.62 | 22.62 6 | 19.25 | 19.96 | 20.75 | 21.50 | 23.50 =========+=========+========+=========+========+========

CEMENT CELLAR FLOORS

=20.= In determining the cost of =cement cellar floors=, the concrete proper and the top coat should be considered separately. The concrete proper is usually reckoned by the cubic yard. About 1 hour more is required to lay a cubic yard of floor than is necessary for plain concrete work. Therefore, in estimating, 25 cents per cubic yard, or the wages of a laborer for 1 hour, must be added to the figures given in Table II. A 1-3-6 mixture is generally used. For stone concrete, then, the cost of the concrete proper for a cement cellar floor would be $5.17 per cubic yard, exclusive of the cost of supervision and the builder’s profit.

An analysis of the cost per square yard of top coat 1 inch thick for a cement cellar floor is as follows:

Cost Cents

¼ hour, plasterer’s time, at 45 cents per hour 11¼ ¼ hour, laborer’s time, at 25 cents per hour 6¼ ¹/₁₅ barrel of cement, at $2 per barrel 13⅓ ⅛ barrel of white sand, at 75 cents per barrel 9⅜ ------ Approximate cost per square yard 40

To the foregoing should be added the cost of supervision and builder’s profit.

CONCRETE BUILDING BLOCKS

=21.= Concrete building blocks usually present about 2 square feet of surface in the wall and are generally 8 inches thick, thus making a volume of 1⅓ cubic feet. Since one-third of this volume as a rule is air space, the actual volume of concrete is a little less than 1 cubic foot. The materials in a block of this kind, if used in a 1-4 mixture, will cost about 18 cents. If the block is 12 inches thick instead of 8 inches, the materials will cost about half again as much, or 27 cents. The cost of labor to manufacture these blocks depends on whether they are made in great quantities, and the wages paid the workmen, etc., and varies from 6 to 10½ cents for each block. To lay a block in the wall costs from 5 to 10 cents, 7 cents being about the average price. This price includes the mortar used in laying. For teaming and haulage, an allowance of 5 cents per block is usually sufficient. The cost per block, 8 inches thick, set in the wall is then as follows:

MAXIMUM COST MINIMUM COST CENTS CENTS Materials 18 18 Labor 10½ 6 Placing 10 5 Haulage 5 none ------ ---- Total 43½ 29

These results divided by 2 will give the cost of the wall per square foot, since each block is supposed to have a surface of 2 square feet. If the wall is 12 inches thick instead of 8 inches, one-half as much again should be added to the price.

MASONRY