Estimating in Building Construction

148 CHAPTER THIRTEEN

corners. This type of accuracy is required only when the
planning of each piece of wood is involved on a series of pro-
jects, such as mass-produced housing, and the amount
becomes significant.

EXAMPLE 13-3 SILL QUANTITY

The exact sill length is shown in the following calculation. However,
the perimeter of 148is sufficient for this example.

Using the building perimeter of 148, the following quantity of sill
material would be purchased. Since most stock lumber comes in
even increments, the purchase quantities have been rounded up to
the nearest stock length. Furthermore, the sill lumber is typically
treated and should be kept separate on the quantity takeoff since
treated lumber is more expensive.

Purchase Quantity

Size Length (lf ) Pieces

2  61010

2 612 4

Total Length  10  10  4  12  148 



Wood Floor Joists. The wood joists should be taken off
and separated into the various sizes and lengths required.
The spacing most commonly used for joists is 16 inches on
center, but spacings of 12, 20, 24, 30, and 36 inches on center
are also found. The most commonly used sizes for floor
joists are 2 6s, 2 8s, 2 10s, and 2 12s, although
wider and deeper lumber is sometimes used. Wood I-joists
(such as TJIs), constructed of engineered lumber, are com-
monly used for joists. Wood I-joists are taken off in the same
manner as 2 joists, except additional time and materials
are needed to provide web stiffeners (Figure 13.6) at the joist
ends and other bearing points.
To determine the number of joists required for any
given area, the length of the floor is divided by the joist spac-

Board feet 1 

2 –  6 –

12

 148 ¿148 bf

Sill length 50 ¿ 50 ¿23 .083¿23 .083¿146 .166¿

Sill length 50 ¿ 0 –  50 ¿ 0 –  23 ¿ 1 –  23 ¿ 1 –

ing, and then one joist is added for the extra joist that is

required at the end of the span. If the joists are to be doubled

under partitions or if headers frame into them, one extra

joist should be added for each occurrence. Factors for vari-

ous joist spacings are given in Figure 13.7.

The length of the joist is taken as the inside dimension

of its span plus 4 to 6 inches at each end for bearing on the

wall, girder, or sill.

Joist Estimating Steps

1. From the foundation plan and wall section, determine
   the size of the floor joists required.


2. Determine the number of floor joists required by first
   finding the number of spaces, then by adding one extra
   joist to enclose the last space.


3. Multiply by the number of bays.


4. Add one extra for partitions that run parallel to the
   joists.


5. Determine the required length of the floor joists.

FIGURE 13.6.Wood I-Joist.

FIGURE 13.7.Joist Spacing Table.