Question 1

How tall does a deck guardrail need to be?

Accepted Answer

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.

Question 2

What is the maximum stair riser height on a deck?

Accepted Answer

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.

Question 3

How far apart can deck balusters be?

Accepted Answer

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.

Question 4

What size bolts for a deck ledger board?

Accepted Answer

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

Guardrail & Balusters

Stairs

Joist & Beam

Ledger Board

Footing

Decking Boards

About these numbers

Run the full check for your county.