How tall does a deck guardrail need to be?

Under IRC R312.1, a deck guardrail must be at least 36 inches high measured from the deck surface. Decks less than 30 inches above grade do not require a guardrail.

What is the maximum stair riser height on a deck?

Under IRC R311.7.5, deck stair riser height must not exceed 7-3/4 inches, and tread depth must be at least 10 inches. The variation between the tallest and shortest riser must be less than 3/8 inch.

How far apart can deck balusters be?

Under IRC R312.1, baluster spacing must not allow a 4-inch sphere to pass through. This is the standard rule adopted by most U.S. counties to prevent a child's head from fitting between balusters.

What size bolts for a deck ledger board?

Under IRC R507.2.1, a deck ledger board must be attached with 1/2-inch lag bolts or through-bolts that penetrate at least 3 inches into solid wood framing, with flashing installed behind the siding.

Deck code quick reference

The numbers inspectors check first — each mapped to its International Residential Code (IRC) section. These are the baseline values most U.S. counties adopt; your county may add stricter amendments.

Guardrail & Balusters

Guardrail height (min): 36 inIRC R312.1
Baluster gap (max sphere): 4 inIRC R312.1
Top rail load resistance: 200 lbsIRC R312.1

Stairs

Riser height (max): 7¾ inIRC R311.7.5
Tread depth (min): 10 inIRC R311.7.5
Riser variation (max): ⅜ inIRC R311.7.5

Joist & Beam

Joist spacing (standard): 16 in o.c.IRC R507.5
Joist hangers required: At beam bearingIRC R507.4
Beam sized to joist span: Per IRC tablesIRC R507.5

Ledger Board

Fastener: ½ in lag/through-boltIRC R507.2.1
Penetration into solid wood (min): 3 inIRC R507.2.1
Flashing: Behind siding, over top edgeIRC R507.2.1

Footing

Hole depth: Below local frost lineIRC R507.3
Diameter (single-span, min): 10 inIRC R507.3
Bearing soil: UndisturbedIRC R507.3

Decking Boards

Fasteners per joist (min): 2IRC R507.9
Board gap for drainage: ⅛ – ¼ inIRC R507.9

About these numbers

These values reflect the IRC model code, which is the baseline adopted (with local amendments) by most U.S. jurisdictions. Frost line depth, guardrail load requirements, and fastener schedules can vary by state and county. Always confirm current requirements with your local building department before construction.

CodeCheckHQ checklist items are general references to common model-code topics; they do not incorporate state-specific amendments or county-level code adoptions. This reference is educational and is not a substitute for AHJ (Authority Having Jurisdiction) approval or professional engineering review.

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