Deck Floor Joist Spacing

To learn more about deck joist sizing spacing and allowable span reference this chart.

Deck floor joist spacing.

We recommend beams are constructed from two 44 x 145mm q deck deck joists and are placed at maximum centres of 1 8m. The larger the deck the larger the joists. In general terms joists spaced 16 inches on center can span 1 5 times in feet their depth in inches. Most composite and pvc decking brands like trex and azek recommend a minimum joist spacing of 16 inches oc.

So when would you ever need to use 12 inches oc. For example joists spaced 16 inches from the center of the joist next to it can span 1 5 times in feet the depth of their inches. The majority of composite deck board brands including trex timbertech and more require deck joists spacing to be at 16 inches o c. Maximum 2x6 deck joist span.

If adding additional framing be sure to keep all boards level and in plane across the tops. Please note that when deck joists are cantilevered they should not extend further than one fourth of the actual adjacent joist span according to irc 2015 r507 5. Section r507 5 notes that deck joists can cantilever up to 1 4 of the joist span. Two by twelve douglas fir joists spaced 12 inches apart on center for example can span 20 feet 7 inches but the same joists spaced 24 inches part can only span 14 feet 7 inches.

But you ll notice when you look at the portion of the span table for joists with cantilevers that the joist span for decks with a cantilever is often less than the span for the same sized joist without cantilevers. The maximum joist spans below are based on a ground snow and live load of 40 pounds per square foot and a dead load of 10 pounds per square foot. As a rule the larger the deck the larger the joists. Some brands like weardeck let you get away with more reinforced with a layer of fiberglass on both the top and bottom weardeck boards easily allow for spans of 24 inches oc.

In this instance the maximum span between deck post centres is 2 07m c16 or 2 24m c24. 2x10 to 15 feet and 2x12 to 18 feet. Spanning 16 6 between supports may cantilever up to an additional 4 1 for a total maximum length of 20 7. Ready to start calculating how much lumber you ll need for your joists.

For example a 2 x 12 joist placed 16 oc. On center for standard straight composite decking installation. Southern pine deck joist maximum spans no cantilever with cantilever joists may cantilever up to of the actual adjacent span. Deck joist spacing should never exceed 16 on center with the exception of max deck boards which allow for maximum 24 on center.