walls. (Fig. 24.) In the second method the membrane is not laid until after the columns and exterior walls are constructed; and it is then carried up the sides of the columns to the height of the hydrostatic head, and up the inside surfaces of the basement-walls to an equal, or greater height. (Fig. 25.)

If the first method is used a sheet of 20-oz, soft-rolled copper should be placed between the plies of the waterproofing beneath all columns, posts, or partitions, under which the unit load exceeds 100 lb per sq in. These COPPER SHEETS

Fig. 24. Membrane-Waterproofing Carried under Columns and on Outside Face of

Outside Walls

should extend from 8 to 12 in beyond the faces of the members and should be thoroughly bonded into the membrane. Great care must be exercised in pouring the concrete, especially at the base of the exterior walls, so as not to injure the membrane. The SEAL OVER THE EXTERIOR WALL-SURFACES, where mechanical protection alone is required, may be a brick veneer, in which the bricks are laid on edge; or a 1-in plaster coat of cement-mortar. When the soil or ground-water is likely to contain DESTRUCTIVE CHEMICALS, however, a

Fig. 25. Membrane-Waterproofing Carried up around Columns and on Inside Face of Outside Walls

solid 4-in concrete wall should be used as a seal; or, what is usually cheaper, owing to the difficulty of bracing the forms for the concrete walls, without tierods or bolts, a 4-in brick wall with a solid mortar bed between the brick and membrane.

The SEAL OVER THE BASEMENT-FLOOR is constructed of sufficient strength to resist the upward pressure of the water, and its thickness depends upon the hydrostatic head. Ordinarily, for low heads a so-called gravity-seal is used, that is, one in which the weight alone of the concrete is sufficient to counterbalance

the pressure. In some cases, however, especially when a considerable pressure is to be resisted, the seal may be constructed as a HORIZONTAL SLAB, reinforced against a uniform upward pressure, and held in place by the loads from columns and walls. If the membrane is applied after the basement columns and walls are in place, the seals on the vertical surfaces are usually constructed of concrete 4 in thick, recessed as shown in Fig. 25. Over the basement floor a gravityseal is used or the mat beneath reinforced to resist the hydrostatic pressure.

CHAPTER XIV

ESTIMATING

1. QUANTITIES

1. Preliminary Procedure. The first step in preparing an estimate is to get a clear idea of the job as a whole. This requires reading the specifications, making a cursory study of the drawings and, if possible, a visit to the proposed site. At this time any correspondence bearing upon the estimate should be studied, any ambiguity in the drawings or inconsistency between them and the specifications cleared up, and a definite decision made in regard to items not plainly set forth. In this connection reference should be made to Chapter XV, Proposals. Having the problem firmly in hand, the Estimator is ready to proceed with the TAKING OFF OF QUANTITIES, which operation is governed by the CHOICE OF UNITS in which the quantities are to be expressed.

2. Estimate-Units. These must be chosen with a view to their suitability for pricing, and also to their adaptability to a proper integration with the general scheme of cost-reporting, estimating, and cost-analysis. In the following articles are given the units which have been found most applicable to each class of work. In general, all quantities are computed in FEET, linear, square, or cubic, except that for steel and iron the POUND is used as the unit. In order to conform to the common practice in the trade, excavation and concrete-work are recorded in CUBIC YARDS.

3. Scaling Drawings. The best means of determining quantities is usually by accurate SCALING from the drawings. When dimensions are given they are used to check the scale-readings. If lists and schedules are shown they can be copied directly into the estimate. INCHES are expressed as FRACTIONS OF A FOOT, to facilitate slide-rule computation.

In using the scale, the horizontal dimensions are first taken from the plans; and the product of any two of these is a HORIZONTAL AREA. Then, using the proper vertical dimensions, taken from the elevations or sections, the VERTICAL AREAS are determined for walls, partitions, etc. Finally, again referring to the plans or sections, the thickness of each element can be read off and the VOLUMES computed. A definite system of procedure should always be followed, as it minimizes the chance of error, facilitates checking, and enables the Estimator to use in subsequent computations information already obtained.

For example, in the case of concrete partitions, the lengths of all such partitions are first scaled from the plans, without deductions for openings, such as windows and small doors. These lengths, multiplied by the partition-heights, taken from the elevations or sections, give one-half the FORM-AREAS (contact

surface). By deducting from this quantity the area of the openings and multiplying the remainder by the partition-thickness, expressed in decimals of a foot, the CONCRETE VOLUME is determined. The product of this same area by the weight of the reinforcement per square foot of partition is the WEight of the STEEL in pounds. Again, for any partition, this area doubled, equal to the Form-area, is the area in square feet for PLASTERING and PAINTING, assuming that both sides of the partition are so treated. From the data thus determined can be computed the areas in square feet of DOORS and WINDOws, and these may be subdivided according to type. The make-up of these values determines the number of linear feet of DOOR-FRAMES and SILLS, which usually constitute a considerable portion of the LIGHT IRON. From the number and size of doors and windows, notation can be made for the HARDWARE required.

No rule can be laid down for the accuracy with which the drawings should be scaled, as this naturally depends upon the class of work and type of estimate. Time is often wasted in going into too much detail, especially when large-scale drawings are available; but the Estimator should guard against making ERRORS OF A CUMULATIVE NATURE, by approximating the quantities for elements of the work which repeat many times. Furthermore, the thicknesses of concrete slabs, drop panels, walls, etc., should be very accurately determined. In the case of steel reinforcement, where large-size bars are used, their lengths should be determined very closely, and no additional amount for waste considered. For small bars, however, including the slab-reinforcement of beam-and-girder floors and of walls, about 10% is usually required for laps, bends, and waste, in addition to the quantity shown on the drawings.

4. Tabulating Quantities. All dimensions scaled from the drawings are to be written on the QUANTITY-SHEET under the captions of the items to which they pertain. No scratch paper should be used, and each step of every operation should be clearly indicated. From the QUANTITY-SHEET the total quantity of each item is to be carried forward to the ESTIMATE-SHEET.

The list of items shown on pages 388 to 392, drawn up by a committee of the New York Building Congress, may be used as a checking list and as a guide in determining a LOGICAL SEQUENCE for tabulating the quantities.

5. Checking Quantities. After transferring the quantities to the ESTIMATE-SHEET, the Estimator should make a series of general checks on the accuracy of his work. For example, he should compare the total floor-slab area with that of the various types of floor-finish and the wall-area below grade with the damp-proofing or water-proofing quantities. All elements of the work, such as columns, footings, etc., for which the total quantities are obtained by multiplying a typical element by the number of times it is repeated, should be again counted. If the computations are made by slide-rule they should be checked by inspection for the accuracy of the first two figures and the position of the decimal point. Additions need not be entirely repeated, but the three left-hand columns of the more important summations should be gone over again. Before pricing the quantities, the Estimator should read the specifications, carefully noting any clauses which particularly affect the cost of the work.

As a final check the total FLOOR-AREA and the CUBIC CONTENTS of the build

ing are to be computed; in order to determine the cost per square foot of floorarea and per cubic foot of contents. These values may be made upon any arbitrary basis, since they serve only as rough comparisons between similar estimates; but it is usual to consider floor-areas as extending to the outside face of exterior walls or spandrel-beams, and heights from the bottom of the cellar floor to the top of the roof-slab. These quantities may well be written at the top of the first

sheet of the final-estimate where the square-foot and cubic-foot prices should be recorded.

6. Footings. All footings of the same type and size are grouped together on the QUANTITY-SHEET and the column-numbers in each group tabulated. On this sheet are computed the CONCRETE-VOLUME, FORM-AREA, and STEELWEIGHT for each class of footing.

For the pyramidal footing the amount of concrete is computed by using the formula for the volume of a frustum of a pyramid. To this amount is added