Deck Joist Span Reference
AWC DCA 6 Table 2. A prescriptive lookup, not a design — your building department has the final say.
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My deck
- Date
- Species
- Grade stamp
- Joist size
- Spacing
- SPAN NEEDED
- ALLOWABLE SPAN
- Span to spare
- Overhang wanted
- MAX OVERHANG
- Joists
- Permit no.
- Inspection date
Southern Pine — max joist span
- 2x6 at 12 / 16 / 24 in
- 9'11" / 9'0" / 7'7"
- 2x8 at 12 / 16 / 24 in
- 13'1" / 11'10" / 9'8"
- 2x10 at 12 / 16 / 24 in
- 16'2" / 14'0" / 11'5"
- 2x12 at 12 / 16 / 24 in
- 18'0" / 16'6" / 13'6"
Douglas Fir-Larch / Hem-Fir / SPF
- 2x6 at 12 / 16 / 24 in
- 9'6" / 8'4" / 6'10"
- 2x8 at 12 / 16 / 24 in
- 12'6" / 11'1" / 9'1"
- 2x10 at 12 / 16 / 24 in
- 15'8" / 13'7" / 11'1"
- 2x12 at 12 / 16 / 24 in
- 18'0" / 15'9" / 12'10"
Redwood / W. Cedar / Ponderosa / Red Pine
- 2x6 at 12 / 16 / 24 in
- 8'10" / 8'0" / 6'10"
- 2x8 at 12 / 16 / 24 in
- 11'8" / 10'7" / 8'8"
- 2x10 at 12 / 16 / 24 in
- 14'11" / 13'0" / 10'7"
- 2x12 at 12 / 16 / 24 in
- 17'5" / 15'1" / 12'4"
What the table assumes
- Live load
- 40 psf
- Dead load
- 10 psf
- Lumber grade
- No. 2
- Service condition
- wet
- Deflection limit
- L/360
- Span measured
- FACE of support to face of support
- Span excludes
- the overhang
- ⚠ Overhang cap
- table figure OR span/4, whichever is less
- ⚠ Joist length ceiling
- 18 ft (DCA 6, footing design)
- ⚠ Ledger minimum
- 2x8 nominal
- ⚠ Guard post joist minimum
- 2x8 nominal
- ⚠ Hot tub, roof, heavy snow
- NOT covered — get an engineer
- ⚠ Final authority
- your building department
Before you cut anything
- Permit applied for
- Grade stamp checked — species AND No. 2 grade
- Span measured face of support to face of support
- Overhang checked against BOTH limits
- Ledger at least a 2x8
- Any joist carrying a guard post at least a 2x8
- Ledger flashing planned — this is where decks fail
- Ledger fastening to the house structure, not just sheathing
- Joist hangers correct for the size, with the right nails
- Hot tub or roof declared to the inspector
- Local amendments checked with the building department
- Inspection booked before anything is covered up
This is a lookup, not a design
DCA 6 is a prescriptive guide — pre-approved answers for ordinary cases. It knows nothing about your soil, a hot tub, a roof or your snow load. Your building department has the final say, and a permit and inspection are not optional.
Spacing is the cheap lever
A Southern Pine 2x10 goes from 11'5" at 24 in centres to 14'0" at 16 in — two and a half feet of span for a few more joists. Going up a nominal size means deeper lumber across the whole deck, and often deeper beams too.
The ledger is where decks fail
Collapses overwhelmingly happen at the connection to the house, not in the middle of a joist. Flashing and fastening into real structure matter more than any span in this table.