This page lists typical International Residential Code (IRC) values as a reference only. The IRC is a model code — your city, county, or state may have adopted a different version or added local amendments. Always verify requirements with your local building department before designing or building. Nothing on this page constitutes engineering or legal advice.
Deck Code Requirements: A DIY Reference
A practical reference of typical IRC values for deck framing, railings, stairs, and footings. Use this as a starting point — your local building department has final authority.
Why deck codes exist
Deck collapses injure thousands of people every year in the United States. Most failures happen at connections — where the ledger meets the house, where posts meet beams, or where railings attach to posts. Building codes encode minimum standards that, if followed, produce a structurally safe deck.
The IRC (International Residential Code) is the baseline that most US jurisdictions adopt, often with local amendments. Some states and counties are stricter. California, Florida, and seismically active areas frequently have additional requirements.
Footings
| Requirement | Typical IRC Value |
|---|---|
| Frost depth | Varies by location — 12" (Deep South) to 48"+ (Minnesota). Check local codes. |
| Min. footing diameter | 12" typical; varies by load calculations |
| Spacing | Max 8 ft on center along beam, commonly |
| Concrete mix | Min. 2,500 PSI (standard 80 lb bag yields ~0.6 cu ft) |
Framing
| Component | Typical Value |
|---|---|
| Joist spacing | 12", 16", or 24" on center — depends on span and decking product |
| Common joist size | 2×8 or 2×10 for most residential decks (check span tables) |
| Joist hanger | Required at all joist-to-beam and joist-to-ledger connections |
| Lumber treatment | UC4A minimum for above-ground framing; UC4B for ground contact |
| Ledger fasteners | ½" lag screws or structural bolts per IRC Table R507.9.1.3 |
| Ledger flashing | Required — self-adhering membrane or equivalent |
Joist spans are determined by species, grade, spacing, and load. Use the deck calculator to estimate joist count, then verify sizing with your building department or a structural engineer.
Railings (Guards)
| Requirement | Typical IRC Value |
|---|---|
| When required | Any deck surface 30" or more above grade |
| Min. height | 36" for decks < 30" above grade; 42" for > 30" (verify locally) |
| Baluster spacing | Max 4" gap — a 4" sphere must not be able to pass through (R312.1.3) |
| Load rating | 200 lb concentrated load at any point; 50 lb/LF uniform load |
| Post attachment | Must be secured to structural framing — not just decking surface |
Stairs
| Requirement | Typical IRC Value (R311.7) |
|---|---|
| Max riser height | 7-3/4" (7.75") |
| Min tread depth | 10" (measured horizontally) |
| Min stair width | 36" clear |
| Handrail requirement | Required when 4 or more risers |
| Handrail height | 34"–38" above stair nosing |
| Stringer size | 2×12 typical; min 3.5" net section after cut |
| Stringer count | Min 3 for 36" width; no span > 16" |
Ledger attachment
The ledger board — the board that attaches your deck to the house — is the single most code-scrutinized element of an attached deck. Failures here can cause the entire deck to collapse.
- → Ledger must attach to band joist or blocking — not to sheathing alone
- → Flashing must prevent water infiltration — inspect every 1–2 years
- → Fastener size, length, and pattern is prescribed by IRC Table R507.9.1.3
- → Ledger connections are usually inspected before closing the framing
Calculate materials for your compliant deck
Use our free calculators to estimate board counts, joist spacing, stringer lengths, and baluster gaps — all with code-compliance checks built in.
Always verify with your local building department
The values on this page come from the model IRC and are provided as a planning reference only. Your jurisdiction may have adopted a different code version, added local amendments, or imposed stricter requirements. Never design or build a deck based solely on this page. Contact your local building department to confirm applicable codes, and have a licensed professional review your plans when in doubt.