Estimating Slate Quantities and Costs

Architects and others interested should confer with local roofing contractors and through them obtain the "per square" or approximate total price for a particular type of roof, or have them estimate the quantities required and furnish a definite price for each individual roof. Producers are always glad to cooperate with roofing contractors to furnish architects a layout or recommendations for slate suitable for any design or desired effect and to furnish roofing contractors estimates so they can give architects or owners comparative cost data to assist them to arrive at amount to spend for slate roof.

A mistake frequently made is that of measuring the roof surface and assuming it as the exact or very close approximate quantity required, then multiplying it by a price quoted in the price-list of one of the slate companies and perhaps adding an assumed sum for labor and contractors' profit.

In preparing estimates for a slate roof, every roofing contractor has his own method of making compensating allowances for waste, breakage, projections through roofs, dormers, hips, ridges, valleys and other factors occasionally entering into the question of quantity and labor. These are usually based upon experience with his own regular labor, local conditions or practice, and possibly other items peculiar to a locality. The following suggestions are therefore offered mainly for architects and others not actively engaged in selling and laying slate roofs, as a guide to many factors which should to be taken into consideration. For rough estimates a good roof costs from 6 to 8 per cent of total cost average building or home.

From the time work is first started at the quarry until the material is laid on the building, there are certain costs which must be taken into consideration. These may be listed as follows:

1. Cost of slate (punched) on cars at the quarry.
2. Freight from quarry to destination.
3. Loading and hauling to storage yard.
4. Unloading, piling arid waste at storage yard.
5. Loading and hauling to job.
6. Unloading and piling at job.
7. Placing on roof and laying. (a) Roofing felt. (b) Elastic Cement. (c) Nails. (d) Snow guards, or Snow Rails. (e) Sheet Metal. (f) Labor, including compensation insurance. (g) Waste in handling, cutting and fitting.
8. Contractor's overhead on organization and equipment
9. Cost of guarantee or Bond.
10. Contractor's profit.

Items 3 and 4 are omitted when material is hauled direct to the job and unloaded. Freight to any locality from a quarry remains a fixed charge based upon either carload or less than carload lots. Less than carload lots carry a freight charge about double that of carload quantities. The question of loading, hauling, unloading and laying depends upon local labor costs, how fast the men work and nature of the contractor's equipment. Some roofing contractors have slate punching machines and buy their slate unpunched, punching same at the job or in the yard on idle days or during inclement weather.\

While it may seem a comparatively simple problem to estimate the net quantity, it is not so easy to allow for the additional material required for slate around chimneys, dormers, hips, valleys, etc. These allowances depend largely upon the judgment and experience of the estimator and the roof design.

Method Suggested for Estimating a Slate Roof

1. Obtain the net area of the roof in square feet, adding 6" to rafter length to allow for waste of normal roof.
2. Deduct one-half of the area of chimneys and dormers if over 20 sq. ft. and less than 80 sq. ft. Make no deduction if less than 20 sq. ft., and deduct 20 sq. ft. less than actual area if more than 80 sq. ft.
3. Include areas of dormer roofs, sides of dormers if slated, slate saddles, or other places where slate is used in addition to the main roof area. Include over- hanging parts of dormers, etc.
4. Add 1 sq. ft. for each lineal foot of hips and valleys, for loss in cutting and fitting.
5. Allow from 2% to 15% additional slate, depending upon the extent to which the roof is intersected by other roofs, dormers, walls, other contingencies, etc.
6. Divide the total of the above by 100, which will give the number of "squares" of roofing required.

It should be noted that slate is always sold at the quarry on the basis of the quantity required to cover d sq. ft." or a "square" of roof when slate is laid with a 3" head lap. If the roof is flat or other than 3" lap is used, the quantity must be corrected to the equivalent amount required as though the 3" lap was used. The following information should be given local roofing contractor when asking for a price:

1. Kind and color of slate.
2. Size of slate desired, stating length and "all one width" or random width.
3. Thickness, as "commercial standard," 1/4", 3/8" etc.
4. Type of roof, as standard, textural, graduated or flat.
5. Kind of nails, as zinc clad, zinc, "yellow metal," copper clad or copper.
6. Kind of valleys and flashings.
7. If hip or gable roof.
8. Kind of snow guards, as galvanized, yellow metal or copper.
9. If snow rails, size of pipe and number of rows of pipe.
10. Location of job; if in city or vicinity, or out of city.
11. When job is to be finished.

Prices

Many requests have been received from architects and builders for the inclusion in this site of a definite list of prices for the various grades and colors of roofing slates. The compilers regret that it is impracticable to do this, for several reasons. The Association recommends, therefore, that when an architect or builder de sires the price of any particular grade and color of slate, he consult his local slate roofing contractor for estimates for the slate in place on the roof. Such estimates will then include the many factors listed in the section on "Estimating," all of which must be given consideration. This can best be given by responsible contractors who are familiar with local conditions and costs.