Rafter Span Chart

Maximum Horizontal Spans for 2x4 through 2x12

Rafter span is the horizontal distance a rafter covers — the run measured on plan — not the sloped length of the board, and that distinction causes more DIY framing errors than any other. On a 6:12 roof the board is about 1.118 times the run, so a 14 foot span means roughly a 15 foot 8 inch rafter before the overhang tail. This chart gives representative maximum spans for 2x4 through 2x12 at 12, 16 and 24 inch on centre spacing as planning figures, then explains everything that moves those numbers: spacing, because 24 inch centres load each rafter about 50% more than 16 inch, lumber species and grade, ground snow load, the dead load of tile or slate versus asphalt, and the deflection limit required when drywall hangs below. Allowable spans are ultimately set by the code edition your jurisdiction has adopted, so verify with local tables or a structural engineer before buying lumber. If your span is too long, the fixes are deeper lumber, tighter spacing, a purlin and struts, an interior bearing wall or designed ridge beam, or engineered lumber and trusses.