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Floor Joist Span Tables (Treated Southern Pine)
Maximum span (feet-inches) for treated southern pine floor joists (40 PSF Live Load, 10 PSF Dead Load)
| Joist Size | Spacing 12″ O.C. | Spacing 16″ O.C. | Spacing 24″ O.C. |
|---|---|---|---|
| 2 x 6 | 9′-6″ | 8′-8″ | 7′-2″ |
| 2 x 8 | 12′-6″ | 11′-5″ | 9′-4″ |
| 2 x 10 | 15′-10″ | 14′-6″ | 11′-11″ |
| 2 x 12 | 19′-3″ | 17′-7″ | 14′-4″ |
| Joist Size | Spacing 12″ O.C. | Spacing 16″ O.C. | Spacing 24″ O.C. |
|---|---|---|---|
| 2 x 6 | 10′-4″ | 9′-5″ | 7′-9″ |
| 2 x 8 | 13′-8″ | 12′-5″ | 10′-2″ |
| 2 x 10 | 17′-5″ | 15′-10″ | 13′-1″ |
| 2 x 12 | 21′-2″ | 19′-3″ | 15′-9″ |
Note: Spans based on NC Residential Building Code. Assumes normal loading conditions and proper support/attachment. Consult local building department for specific requirements.
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NC Residential Building Code for Decks
General Requirements
- Minimum live load: 40 psf
- Maximum allowable deflection: L/360
- All lumber must be pressure-treated or naturally durable
- All fasteners and hardware must be corrosion-resistant
Ledger Attachment
- ½” lag screws or through-bolts required
- Minimum 2 fasteners per joist
- Flashing required above ledger
- Cannot attach through exterior veneers
- Proper spacing from ends and edges required
Guardrails
- Required when deck is >30″ above grade
- Minimum height: 36″ residential, 42″ commercial
- Maximum opening: 4″ sphere cannot pass through
- Must resist 200 lb concentrated load
Stairs
- Maximum riser height: 7¾”
- Minimum tread depth: 10″
- Minimum stair width: 36″
- Handrails required for 4 or more risers
- Handrail height: 34″-38″
Footings
- Must extend below frost line (minimum 12″)
- Minimum size: 8″ diameter
- Must bear on undisturbed soil
- Post must be anchored to footing
Post Requirements
- Minimum size: 6×6 for heights over 8′
- Maximum height: 14′ free-standing
- Must be naturally durable or preservative-treated
- Proper connection to beam required
Beam Requirements
- Multiple-ply beams must be fastened together
- Maximum post spacing per span tables
- Beam splices must occur over posts
- Proper bearing required at beam ends