Tributary Area
The floor, roof, or wall area that contributes load to a specific structural member. Calculated as the member spacing times the span it supports.
In Detail
Tributary area determines the total load a beam, column, or footing must carry. For a beam supporting floor joists on both sides: tributary width = half the joist span on each side. Total tributary area = tributary width × beam length. Multiply tributary area by the floor load (psf) to get total load. This load is then used to size the beam and its supporting posts and footings.