Estimating in Building Construction

145

WOOD

CHAPTERTHIRTEEN

13–1 Frame Construction

The wood frame construction discussed in this chapter
relates primarily to light construction of ordinary wood
buildings. It covers the rough carpentry work, which includes
framing, sheathing, and subfloors. Flooring, roofing, drywall
and wet wall construction, and insulation are all included in
their respective chapters, and discussions of them are not
repeated here.
The lumber most commonly used for framing is yard or
common lumber; the size classification of lumber most
commonly used is dimensional (2 to 4 inches thick and in a
variety of widths). The allowable spans of wood depend on
the loading conditions and the allowable working stresses
for the wood. As higher working stresses are required, it may
become necessary to go to a stress-grade lumber that has
been assigned working stresses. This type of lumber is
graded by machine testing and is stamped at the mill. This
information is available in the pamphlet from your local
lumber supplier.
Rough lumberis wood that has been sawed, edged, and
trimmed, but has not been dressed. When lumber is surfaced
by a planing member, it is referred to as dressed.This process
gives the piece a uniform size and a smooth surface. Before
the lumber is dressed, it has the full given dimension (i.e.,
2 4 inches), but once it has been surfaced on all four sides
(S4S), it will actually measure less. For example, a 2 by 4
is actually 1^1 ⁄ 2 inches by 3^1 ⁄ 2 inches. The full size of lumber is
referred to as its nominal size and is the size by which it is
quantified and purchased.

The only safe way to estimate the quantity of lumber

required for any particular job is to do a takeoff of each piece

of lumber needed for the work. Since the time needed to do

such an estimate is excessive, tables are included to provide

as accurate material quantities as are necessary in as short a

time as possible. These are the methods generally used.

13–2 Board Measure

When any quantity of lumber is purchased, it is priced and

sold by the thousand feet board measure, abbreviated mbm

or more commonly mbf(thousand board feet). The estimator

must calculate the number of board feet required on the job.

One board foot is equal to the volume of a piece of

wood 1 inch thick and 1 foot square (Figure 13.1A). By using

Formula 13-1, the number of board feet can be quickly

determined. The nominal dimensions of the lumber are

used even when calculating board feet.

Formula 13-1

NNumber of feet (board measure)

PNumber of pieces of lumber

TThickness of the lumber (in inches)

WWidth of the lumber (in inches)

LLength of the pieces (in feet)

12 inches (one foot), a constant—it does not change

Board Foot Measurement

NP

TW

12

L

EXAMPLE 13-1 CALCULATING BOARD FEET

Estimate the board feet of 10 pieces of lumber 2 6 inches and
16 feet long (it would be written 10–2 6s @ 16 0 (see Figure 13.1B).

Board Feet 10 

2 –  6 –

12 –

 16 ¿160 bf

This formula can be used for any size order and any number of

pieces that are required. Figure 13.2 shows the board feet, per piece,

for some typical lumber sizes and lengths. Multiply the board feet

by the number of pieces required for the total fbm.