This section is from the book "The Building Trades Pocketbook", by International Correspondence Schools. Also available from Amazon: Building Trades Pocketbook: a Handy Manual of reference on Building Construction.
The rough lumber used in framing is measured by the board foot, which means a piece 12 in. square and 1 in. thick. Lumber is always sold on a basis of 1,000 feet board measure; the customary abbreviation for the latter term is B. M., and for thousand is M; thus, 500 ft. board measure, costing $14.00 per thousand, would be written: 500 ft. B. M. at $14.00 per M.
To obtain the number of board feet in any piece of timber, the length of the scantling in inches may be multiplied by the end area in sq. in., and the result divided by 144. For example, the number of feet B. M. in a floor joist 20 ft. long, 3 in. thick, and 10 in. deep, will be 240 in. (= 20 ft. X 12) multiplied by 30 sq. in. (the end area), or 7,200 sq. in., 1 in. thick; dividing by 144, the result is 50 ft. B. M.
The rule used by most contractors and lumber dealers is as follows: Multiply the length in feet by the thickness and width in inches, and divide the product by 12. Thus, a scantling 26 ft. long, 2 in. thick, and 6 in. wide, contains (26x2x6) / 12 = 26ft.B.M.
This rule, expressed in a slightly different manner more convenient for mental computation, is: Divide the product of the width and thickness in inches by 12, and multiply the quotient by the length in feet. Thus, a 2" X 10" plank, 18 ft. long, contains [(2x10) / 12] x 18 = 30 ft. B. M.
To calculate the number of studs, set on 16" centers, the following rule may be used: From the length of the partition deduct one-fourth, and fa this result add 1. Count the number of returns, or earners, on the plan, and add two studs for each return. (The reason for adding 1 is to include the stud at the end, which would otherwise be omitted.) The sills, plates, and double studs must be measured separately.
For example, the total number of studs required for the lengths of partitions given at the left is as follows:
Deducting one-quarter of 60 ft. from it, the remainder is 45; adding 1 stud, the result is 46. If there are, say, 4 returns, at 2 studs each, the total number is 46 + 8 = 54 studs.
As a general rule, when (as is usual) the studs are set at 16" centers, 1 stud for each foot in length of partition will be a sufficient allowance to include sills, plates, and double studs. Thus, if the total length of partitions is 75 ft., 75 studs will be sufficient for sills, double studs, etc. If the studs are set at 12" centers, the number required will be equal to the number of feet in length partition plus one-fourth. Thus, if the length of partitions is 72 ft.. 72 +18, or 90 studs, will include those required for sills, plates, etc.
The same rules may be used for calculating the number of Joists, rafters, tie-beams, etc.
A good way to estimate bridging is to allow 2 cents a piece, or 4 cents a pair; this will be sufficient to furnish and set a pair made of 2" X 3" spruce or hemlock stuff.
To calculate sheathing or rough flooring (which is not matched), find the number of feet B. M. required to cover the surface, making no deductions for door or window openings, for what is gained in openings is lost in waste. If the sheathing is laid horizontally, only the actual measurement is necessary, but. if it is laid diagonally, add 8 or 10 per cent.totheactualarea. In sheathing roofs where many hips, valleys, roof dormers, etc. occur, there will be a great deal of waste material caused by mitering the boards, fitting around cheeks of dormers
30 ft. 6 in.
10 ft. 6 in.
9 ft. 6 in.
5 ft. 0 in.
4 ft. 6 in.
60 ft. 0 in.
and forming saddles behind chimneys. This waste is not readily calculated and must be determined by the actual conditions as well as by the care exercised by the men in utilizing the cuttings. In covering large areas a great deal of material can be saved by ordering the lengths of boards to suit the spacing of the rafters.