floor-area is often necessary where the rapidity of work requires considerable re-posting. For wall-forms, as ordinarily constructed, there are required for 1 000 sq ft of form-area, 3 000 sq ft board-measure of form-lumber. Then, If the wall-forms are to be used four times, the result is: Cost of making wall-forms = $0.252/4 = $0.063 per sq ft of WALL-AREA. For columns, 4 sq ft of lumber is required for 1 sq ft of form-area; the cost is therefore, $0.084 X 4 = $0.336 per sq ft of FORM-AREA (contact surface). As the COLUMN-FORM-AREA is computed for only one story-height, there is no deduction for number of uses. It should be remembered that the AMOUNT OF LUMBER REQUIRED to form a given surface depends upon many variable factors, and cannot be stated arbitrarily. Each Estimator should work out for himself the number of boardfeet needed for the various standard designs employed by his firm, bearing in mind the requirements of bracing, shoring, and re-posting, which latter is often necessary, in rapid construction, for three stories beneath that actually formed. Having determined the UNIT PRICE OF MAKING FORMS, a percentage is added for waste which varies according to conditions, but should average about 15% of the values just computed for floors and walls and about one-half that amount for columns. Then, combining the cost of MAKING FORMS with the COST OF PLACING, taken from the cost-records previously quoted, the following UNIT PRICES Covering all labor and material result: = Floor-forms (girderless type), $0.168 + $0.02 + $0.12 $0.308 per sq ft of floor-area. = Wall-forms, $0.063 + $0.01 + $0.15 $0.223 per sq ft of wall-area. = $0.356 per sq ft of column Column-forms, placing, $1.70 per lin ft of columns. Thus, starting with the cost of lumber per thousand square feet, boardmeasure, adding incidentals plus the labor of receiving and making, and multiplying by a factor representing the number of feet required per square foot of form-area, there is developed in each case the cOST OF LABOR AND MATERIAL IN MAKING FORMS for all classes of work. This value, divided by the number of uses, increased by a percentage for waste, and added to the cost-unit for erecting, gives the total price for each estimate-item. In this manner are developed, also, the unit prices of the form-work for sills, copings, stairs, etc. 5. Steel Reinforcement. Combining the labor-prices and material-prices as given in Paragraph 2, Assumed Material-Prices and Labor-Units, the computation is arranged as follows: Reinforcement, per cwt, f.o.b. cars at the mill, = $3.00 If it is necessary to compute separately the cost of labor and material for the different classes of reinforcement, the procedure is in all cases the same. 6. Granolithic Floor-Finish. Floor-finish is preferably laid monolithic with the base, but when weather-conditions or other causes make this impracticable the estimate should include an allowance for thoroughly cleaning the surface to be finished; more material, also, is required than in the former case. Using again the assumed LABOR-PRICES and MATERIAL-PRICES, the following results are obtained: Monolithic floor-finish (average thickness 1 in), For 1000 sq ft of surface: Note that the price of the grit is the difference between the cost of that material and the crushed stone which latter has already been included in the cost of the concrete of the floor. Unit price = $76.30/1 000 sq ft = $0.076 per sq ft of surface. Non-monolithic floor-finish (average thickness 11⁄2 in). 7. Exterior Wall-Finish. For purpose of illustration, it is assumed that the exterior surfaces of the building are to be pointed and washed down with a mixture of white cement and white sand. In such work, with average conditions, 1 bbl of cement mixed with 8 cu ft of sand covers about 1 000 sq ft of surface, if mixed to the consistency of heavy whitewash and applied with a brush. The amount of material and labor required in preliminary pointing depends entirely upon the quality of the concrete-work and can only be approximated. This item, however, is usually so small a proportion of the total estimate that a precise calculation is unnecessary. The following is a typical computation for washing the exterior surfaces after preliminary pointing has been done. If the walls are finished by rubbing with carborundum block, instead of merely washing down, about one-half barrel of cement is required for each 1 000 sq ft of wall surface, and the labor cost of going over the wall twice varies between $5.00 and $8.00 per 1 000 sq ft depending upon the wages paid, and the care expended upon the work. 3. SUBCONTRACTS, OVERHEAD COST, AND PROFIT 1. Subcontracting Work. Each contractor follows his own individual method in subletting portions of the general contract. Usually, beside the five major items of heating, plumbing, lighting, elevators, and sprinklers, together with any mechanical equipment, there are a number of smaller items such as roofing, sheet-metal work, glazing, pipe-rails, etc., which it is customary for the GENERAL CONTRACTOR to sublet. Again, especially in city work, the difficulties of excavation, sheet-piling, shoring, and under-pinning are such that Contractors specializing in these classes of work can usually make their own profit and still perform the operation for less money than the GENERAL CONTRACTOR. In these articles the term SUBCONTRACT is used only in referring to those agreements which require labor to be performed on the job, as distinguished from the purchase of fabricated materials. WHERE. The most important caution in regard to SUBCONTRACTS, as affecting the estimate, is to make sure that they COVER ALL THE WORK NOT INCLUDED ELSEThis requirement seems obvious; but the lack of co-ordination and the resulting gaps between the operations of different trades, all of which must be filled in at the GENERAL CONTRACTOR'S expense, are often very costly matters. 2. Estimate-Information for Subcontracts. It is customary for each SUBCONTRACTOR to take off his own quantities from the drawings and specifications in the GENERAL CONTRACTOR'S or ARCHITECT's office, and to make a lump-sum bid on his portion of the work. Many times, however, when there is no opportunity to get such a figure, nor to thus place upon the SUBCONTRACTOR the just responsibility for his own quantities, it becomes necessary to use a unit price in the estimate. For this purpose, and also to check the subcontractors' proposals, the Estimator should compute the approximate quantities of work under each item as follows: Heating: Cubical contents of spaces heated by different types of radiation. Sprinklers: Number of heads and square feet of floors protected. Roofing: Square feet of surface. Pipe-Rail: Linear feet of rail of different sizes. These units are then priced and the total amount extended, as in the case of the other estimate-items. 3. Overhead Expense. Having completed the estimate for the labor, material, and subcontracts entering into a prospective job, it remains to price the items of OVERHEAD EXPENSE, CONTINGENCY, and PROFIT. OVERHEAD EXPENSE divides into two general classifications: the items which vary in cost according to the amount of work to be done, and those which depend upon the duration of the work. The first class comprises Liability and Fire Insurance, Office Expense, Installation, Tools, Supplies, Cutting, Cleaning, Pointing, and General Expense, such as time lost by straight-time men, toolhouse attendants, etc. The second class comprises Plant-Rental, Supervision, and Telephone. It should be noted that some of the items under the heading of Overhead Expense include actual job labor and material, but as their evaluation is not based upon a quantity survey, they can best be considered as a percentage of the more tangible part of the estimate. For the purpose of estimating OVERHEAD EXPENSE it is satisfactory to take a percentage of the CONCRETE-COST of the job; but items which depend upon the duration of the work should be checked by a direct estimate based on the monthly expense of plant and personnel. The CONCRETE-COST of a job is determined by taking the sum of all labor and material, exclusive of subcontracts, and deducting the last five items of the labor-classifications and the last eight items of the material-classifications. (See Chapter XVII, pages 462 to 456.) If there is a probability of the work running into cold weather, an allowance should be made under that heading in the OVERHEAD EXPENSE rather than the inclusion of such increased cost with the items affected. As the weather is always an unknown factor, the COST-ANALYSIS SYSTEM has been designed with a separate classification for such expense. Whether or not an ITEM OF CONTINGENCY should be included depends upon the adequacy of the information upon which the estimate is based, the extent to which it is covered by reliable sub-bids, and the type of contract to be entered into in case the proposal is accepted. In general, the inclusion of a large con tingency is merely a tacit acknowledgment that the estimate is considered untrustworthy; but if doubt actually exists in regard to the probable labor-costs, it is much better to include a LUMP-SUM CONTINGENCY than to bolster up each item. 4. Profit. The question of the AMOUNT OF PROFIT to be added to an estimate is purely a matter of policy determined by probable operating-costs and by what the type of work, proposal-conditions, etc., will justify. List of Estimate Headings from the Report of the Committee Appointed to Study Estimating and Cost Keeping for Reinforced Concrete Building Construction by the New York Building Congress. The following list of classifications includes only work done directly by the general contractor. Work ordinarily sublet, as for instance general excavation, is not analyzed in this report. The number of sub-headings under each classification has been made as small as possible, in order to concentrate attention on the important ones. For example under the heading "Brickwork" the obvious sub-divisions of "Face Brick," "Common Brick,' 'Paving Brick," etc. are entirely omitted, because the danger of omitting all the paving brick from an estimate is less than the danger of omitting proper allowance for mortar, mortar color, mortar tubs, scaffold plank and horses. |