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Deck joist span chart

The 2021 International Residential Code gives maximum spans for deck joists in Table R507.6, for No. 2 lumber with a wet-service factor, a 40 psf live load and 10 psf dead load. A Southern pine 2 × 8 at 16 inches on center spans 11′-10″, a 2 × 10 spans 14′-0″ and a 2 × 12 spans 16′-6″. This page starts with a 14-foot span in Douglas fir-larch, hem-fir or SPF, which needs a 2 × 12 at 16 inches.

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      Where snow loads are higher than 40 psf, the code has separate, shorter spans. Always check with your local building department, which may use a different code edition.

      How the deck calculator works

      DeckCalc assumes the deck boards run parallel to the house and the joists run out from a ledger on the house to a beam near the outer edge. Rows of boards = depth × 12 ÷ (board width + gap), rounded up. Boards = rows × deck length × (1 + waste) ÷ board length, rounded up. Joists = length × 12 ÷ spacing, rounded up, plus one. Screws = rows × joists × screws per joist.

      Deck joist spans (IRC 2021 Table R507.6)

      SpeciesSize12″ o.c.16″ o.c.24″ o.c.
      Southern pine2×69′-11″9′-0″7′-7″
      2×813′-1″11′-10″9′-8″
      2×1016′-2″14′-0″11′-5″
      2×1218′-0″16′-6″13′-6″
      Douglas fir-larch, hem-fir, SPF2×69′-6″8′-4″6′-10″
      2×812′-6″11′-1″9′-1″
      2×1015′-8″13′-7″11′-1″
      2×1218′-0″15′-9″12′-10″
      Redwood, western cedars, ponderosa / red pine2×68′-10″8′-0″6′-10″
      2×811′-8″10′-7″8′-8″
      2×1014′-11″13′-0″10′-7″
      2×1217′-5″15′-1″12′-4″

      No. 2 grade, wet service factor, 40 psf live load, 10 psf dead load, deflection L/360, no cantilever. Higher snow loads need shorter spans.

      Maximum joist spacing for decking (IRC Table R507.7)

      DeckingPerpendicularDiagonal
      1¼″ (5/4) wood16″12″
      2″ wood24″16″
      Composite / plasticPer the manufacturer's span rating (ASTM D7032); 16″ and 12″ are typical

      Results are material estimates. Span values are from the 2021 International Residential Code; your jurisdiction may use another edition or local amendments, and beams, posts, footings, ledger attachment and guards need their own design. Check with your building department before you build.

      Frequently asked questions

      How far can a 2×8 deck joist span?

      At 16 inches on center: 11′-10″ for Southern pine, 11′-1″ for Douglas fir-larch, hem-fir or SPF and 10′-7″ for redwood or western cedar (IRC 2021).

      How far can a 2×10 deck joist span?

      At 16 inches: 14′-0″ Southern pine, 13′-7″ Douglas fir-larch / hem-fir / SPF, 13′-0″ redwood or cedar.

      Can joists cantilever past the beam?

      Yes, within limits: up to one quarter of the joist span or the cantilever length in Table R507.6, whichever is less.

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      Yes, with no sign-up or ads.

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      Yes, in this browser only.

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