Deck Joist Span Tables
Maximum spans for 2x6 through 2x12 joists in Southern Pine and SPF at common spacings, under the 40 PSF live + 10 PSF dead load assumption.
Quick Answer: At 16 inches on center, a 2x8 joist spans up to 11' 10" in Southern Pine #2, or 10' 7" in SPF. A 2x10 at 16" OC spans 14' in Southern Pine, 13' in SPF. Use the full table below for other sizes and spacings.
Maximum Joist Span Table
From IRC R507.5 (2021 edition). Grade #2 lumber, 40 PSF live load + 10 PSF dead load. Spans are from face of support to face of support (not center-to-center).
| Joist Size | Southern Pine #2 | SPF #2 | ||||
|---|---|---|---|---|---|---|
| 12″ OC | 16″ OC | 24″ OC | 12″ OC | 16″ OC | 24″ OC | |
| 2x6 | 9' 11" | 9' 0" | 7' 7" | 8' 10" | 8' 0" | 6' 10" |
| 2x8 | 13' 1" | 11' 10" | 9' 8" | 11' 8" | 10' 7" | 8' 8" |
| 2x10 | 16' 2" | 14' 0" | 11' 5" | 14' 11" | 13' 0" | 10' 7" |
| 2x12 | 18' 0" | 16' 6" | 13' 4" | 17' 5" | 15' 1" | 12' 4" |
Hem-Fir and Douglas Fir-Larch values fall between Southern Pine and SPF. For those species, consult the full IRC R507.5 table or AWC's Prescriptive Residential Wood Deck Construction Guide (DCA 6).
How to Use This Table
Measure the joist span
The span is the distance from the face of the ledger board (or one beam) to the face of the supporting beam (or the other beam). Not the overall deck length, not center-to-center of posts.
Pick your lumber species and grade
Check the stamp on the lumber or ask at the yard. Most pressure-treated decking sold east of the Mississippi is Southern Pine. West Coast is typically Hem-Fir or Douglas Fir. Grade #2 is the code baseline.
Pick your joist spacing
Standard is 16 inches on center. Reduce to 12" OC if you need to span slightly longer than 16" OC allows, or if your decking requires it.
Check the table
Find your size row and spacing column for your species. That number is the maximum allowable span. If your span exceeds it, go to a larger joist or closer spacing.
Check cantilever if applicable
If your joists extend past the beam, the cantilever cannot exceed 1/4 of the back-span. A 10-foot back-span allows 2.5 feet of cantilever maximum.
Common Design Combinations
Typical joist selections for common deck configurations:
Small deck (8' deep)
2x8 @ 16" OC in any species. Room for up to 4' cantilever if needed.
Average deck (10-12' deep)
2x8 in Southern Pine (@ 16" OC) or 2x10 in SPF. Most common residential deck.
Deep deck (14-16' deep)
2x10 in Southern Pine or 2x12 in SPF, both at 16" OC. For SPF 16' deep, consider 2x12 at 12" OC.
Heavy-use deck (hot tub, large gatherings)
Drop to 12" OC spacing with the same size lumber. Or add an intermediate beam to reduce joist span.
Composite decking with 12" OC requirement
Same sizing, just tighter spacing. Allows slightly longer spans than 16" OC for the same joist size.
Snow-load region (40+ PSF ground snow)
Check local amendments. Most places still accept R507.5 tables up to 40 PSF ground snow; above that, engineered design may be required.
Read the lumber stamp
Every piece of framing lumber has a grade stamp indicating species and grade. "Southern Pine #2", "SPF #2", "Hem-Fir #2", etc. If the stamp is cut off or unreadable, you cannot use the prescriptive span tables because you don't know which column applies. Either get stamped lumber or have a structural engineer specify. Some yards sell "utility grade" lumber that does not qualify for structural use — check before you buy.
Frequently Asked Questions
What is a deck joist span?
A joist span is the horizontal distance a deck joist covers between supports — typically from the ledger board (at the house) to the outer beam, or between two beams on a freestanding deck. Longer spans require larger lumber, closer spacing, or a stronger species. IRC R507.5 publishes prescriptive maximum spans so you do not need an engineer for typical residential decks.
What lumber species is most common for deck joists?
In the US, pressure-treated Southern Pine dominates the eastern half of the country and pressure-treated Hem-Fir or Douglas Fir-Larch dominates the west. SPF (Spruce-Pine-Fir) is common in the North. Southern Pine generally allows longer spans than SPF at the same size, which is why the same 2x8 can span 10'6" in SP but only 9'1" in SPF.
What is the 40 PSF live load assumption?
IRC R301.5 requires decks to be designed for a 40 pounds-per-square-foot live load (people, furniture, snow in some regions) plus 10 PSF dead load (the deck itself) = 50 PSF total design load. All published span tables assume this load. If your deck will carry a hot tub or unusually heavy loads, you need engineered design beyond prescriptive tables.
What is the cantilever limit?
IRC R507.5 allows a joist to cantilever (extend past the supporting beam) up to one-quarter of its actual allowable span. Example: a 2x8 joist spanning 10 feet can cantilever up to 2.5 feet past the beam. Cantilevering lets you design a deck whose outer edge extends beyond the beam, which looks cleaner and hides the beam.
Can I use 2x6 joists for a deck?
Yes, for short-span decks. 2x6 joists are common for decks under about 8 feet from ledger to beam. Past that, 2x8 or 2x10 becomes more practical. 2x6 is also common for decks over existing concrete patios where there is no frame height to fill.
What spacing is most common?
16 inches on center is the standard for deck joists. 12 inches on center is used for heavy loads, unusual decking materials (some composites require 12" spacing), or for aesthetic reasons (closer joist shadows show through composite gaps). 24 inches on center is rarely used for decks because most decking is rated for 16" or less.
Does snow load affect the span?
Yes, in regions with significant ground snow. IRC R507 table values assume 40 PSF live load, which covers most snow-region decks, but jurisdictions with ground snow loads above about 50 PSF often reduce allowable spans or require engineered design. Check your local adopted amendments if you are in a heavy-snow region.
Can I exceed the table spans with engineering?
Yes. A licensed structural engineer can analyze your specific deck and produce drawings that allow longer spans, especially with engineered lumber (LVL, I-joists, parallel-strand lumber). Expect to spend $500 to $2,000 for deck engineering. Prescriptive code (the tables) is a free option; engineering is an optional upgrade.
Beam Span Tables
How to size the beams your joists rest on.
Ledger Board Code
Attachment, flashing, and fastener requirements.
All Deck Codes
Complete IRC R507 reference.
Values from the 2021 International Residential Code Section R507.5. Your jurisdiction may have adopted a different edition or local amendments. Cross-reference AWC DCA 6 for additional species. Not engineering advice.