Deck Joist Spacing and Spans
Joists are the horizontal framing members that support the decking surface. Joist size determines maximum span (the distance between supports), and joist spacing determines how many you need. The two decisions are related: wider spacing means fewer joists but each one must span shorter distances or be a larger size.
Maximum Joist Spans (Southern Pine #2)2×6 at 16" OC: 8 ft 6 in span
2×8 at 16" OC: 10 ft 6 in span
2×10 at 16" OC: 13 ft 6 in span
2×12 at 16" OC: 16 ft span
(IRC Table R507.5 residential deck loads)
2×8 at 16" OC: 10 ft 6 in span
2×10 at 16" OC: 13 ft 6 in span
2×12 at 16" OC: 16 ft span
(IRC Table R507.5 residential deck loads)
These spans assume normal residential deck loading (40 psf live load + 10 psf dead load) per the International Residential Code. Hot tubs, planter boxes, and other concentrated loads require shorter spans or doubled joists underneath. Always verify with your local building inspector.