Thu, Sep 13, 2018
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Determining the correct deck joist spacing and span is actually more complicated than you may think. Although building a deck seems straightforward, there are a few important design factors to keep in mind.
Your maximum joist span will depend on the wood species, joist spacing, size and whether the joists will be cantilevered. Unlike interior floor joists, you also have to take into account the direction and size of your decking.
Plus, unlike floor joists, decks needs to be able to support the extra weight of pressure treated wood, handrails, as well as snowfall during winter.
The deck joist span chart below is based on the updated codes from the International Residential Code (2015), which for the first time, specifically addressed these deck design considerations.
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.
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.
Maximum 2x6 Deck Joist Span
| Wood Species | Spacing (O.C.) | Span with No Cantilever | Span with Cantilever |
|---|---|---|---|
| Southern Pine | 12 | 9-11 | 6-8 |
| 16 | 9-0 | 6-8 | |
| 24 | 7-7 | 6-8 | |
| Douglas fir-larch, hem-fir, spruce-pine-fir | 12 | 9-6 | 6-3 |
| 16 | 8-8 | 6-3 | |
| 24 | 7-2 | 6-3 | |
| Redwood, western cedars, ponderosa pine, red pine | 12 | 8-10 | 5-7 |
| 16 | 8-0 | 5-7 | |
| 24 | 7-0 | 5-7 |
Maximum 2x8 Deck Joist Span
| Wood Species | Spacing (O.C.) | Span with No Cantilever | Span with Cantilever |
|---|---|---|---|
| Southern Pine | 12 | 13-1 | 10-1 |
| 16 | 11-10 | 10-1 | |
| 24 | 9-8 | 9-8 | |
| Douglas fir-larch, hem-fir, spruce-pine-fir | 12 | 12-6 | 9-5 |
| 16 | 11-1 | 9-5 | |
| 24 | 9-1 | 9-1 | |
| Redwood, western cedars, ponderosa pine, red pine | 12 | 11-8 | 8-6 |
| 16 | 10-7 | 8-6 | |
| 24 | 8-8 | 8-6 |
Maximum 2x10 Deck Joist Span
| Wood Species | Spacing (O.C.) | Span with No Cantilever | Span with Cantilever |
|---|---|---|---|
| Southern Pine | 12 | 16-2 | 14-6 |
| 16 | 14-0 | 14-0 | |
| 24 | 11-5 | 11-5 | |
| Douglas fir-larch, hem-fird spruce-pine-fir | 12 | 15-8 | 13-7 |
| 16 | 13-7 | 13-7 | |
| 24 | 11-1 | 11-1 | |
| Redwood, western cedars, ponderosa pine, red pine | 12 | 14-11 | 12-3 |
| 16 | 13-0 | 12-3 | |
| 24 | 10-7 | 10-7 |
Maximum 2x12 Deck Joist Span
| Wood Species | Spacing (O.C.) | Span with No Cantilever | Span with Cantilever |
|---|---|---|---|
| Southern Pine | 12 | 18-0 | 18-0 |
| 16 | 16-6 | 16-6 | |
| 24 | 13-6 | 13-6 | |
| Douglas fir-larch, hem-fir, spruce-pine-fir | 12 | 18-0 | 18-0 |
| 16 | 15-9 | 15-9 | |
| 24 | 12-10 | 12-10 | |
| Redwood, western cedars, ponderosa pine, red pine | 12 | 17-5 | 16-5 |
| 16 | 15-1 | 15-1 | |
| 24 | 12-4 | 12-4 |
Maximum Joist Spacing and Decking Material
| Decking Type and Size | Perpendicular to joist | Diagonal to joist |
|---|---|---|
| 1.25-inch-thick wood | 16 inches | 12 inches |
| 2-inch-thick wood | 24 inches | 16 inches |
| Plastic composite | 16 inches | 12 inches |
Considering composite decking? Read our comparison of Trex vs Timbertech
Conclusion
As you can see there are a number of factors to consider before you start building a deck. You will need to determine the type and size of decking you plan to use, then select the type and size of your joist members.
Related Resource: Lumber Dimensions Explained
Each of these decisions will greatly affect your deck joist span distances. Don’t forget to check with your local building department before you start building.
Although most of the United States has adopted the International Residential Code, each county may have local building codes and requirements you need to follow.
Also, if you have questions about deck joist spans you should contact an engineer.
