WOOD BEAM SIZINGTM   Beam cost

At the bottom of the BEAM module, WBS shows both the weight of the beam and the number of board feet of lumber required.

BEAM WEIGHT

Weight is calculated using the actual dimensions: width, depth and length at an average wood density of 40 pounds per cubic foot.

Wood density varies considerably, depending on species and moisture content, so WBS rounds the beam weight to the nearest 10 pounds for most beams. The actual length is the beam span plus bearing on each end, the length that would be cut for installation.

The beam weight for the entire beam - divide the weight by the number of pieces in a built up beam - indicates how hard it will be to install.

BOARD FEET

Board feet is a useful measure of beam cost. WBS calculates the number of board feet of lumber required for the beam. The actual cut length is rounded up to the nearest readily available wood length.

Suppose we have a beam using two-2 x 12's with one jack stud at each end:

In this case, reducing the clear span from 7'-10 to 7'-8 reduces the lumber cost 20 percent.