This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
Board Measure. The rough lumber used in framing is measured by the board foot, which means a piece 12 inches square and 1 inch thick. Lumber is always sold on a basis of a thousand feet board measure; the customary abbreviation for the latter term is B. M.; that for thousand is M; thus, 500 feet 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 is multiplied by the end area in inches, and the result is divided by 144. For example, the number of feet B. M. in a floor joist, 20 feet long, 3 inches thick, and 10 inches deep, will be: 240 in. (=20 ft. X12) multiplied by 30 sq. in. (the end area), and the product divided by 144, giving 50 feet B. M.
The following rule is that used by most contractors and lumber dealers: Multiply the length in feet by the thickness and width in inches, and divide the product by 12. Thus, a scantling 26 feet long, 2 inches thick, and 6 inches wide contains 26x2x6/12 = 26 feet B. M.
This rule, expressed in a slightly different manner, is more convenient for mental computation: Divide the product of the width and thickness in inches by 12, and multiply the quotient by the length in feet. Thus, a 2"xl0" plank, 18 feet long, contains 2 X 10 /12 X 18 = 30 feet B. M.
Studs. To calculate the number of studs-set on 16-inch centers-the following rule may be used: From the length of the partition deduct one-fourth, and to this result add 1. Count the number of returns, or corners, on the plan, and add 2 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 number of studs required for partitions shown on the plan, Fig-. 3, is computed as follows: The lengths are:
Deducting one-quarter from GO feet, the remainder is 45 feet; adding 1 stud, the result is 46 feet. As there are 4 returns, with 2 studs for each, the total number is 46 + (4 X 2) = 54 studs. As a general rule, when (as is usual) the studs are set at 16-inch 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 feet, 75 studs will be sufficient for sills, double studs, etc. If the studs are set at 12-inch centers, the number required will be equal to the number of feet in length of partition plus one-fourth. Thus, if the length of partitions is 72 feet, 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 apiece, or 4 cents per pair; this will be sufficient to furnish and set a pair made of 2" X 3" spruce or hemlock stuff.