How to Build Code-Compliant Deck Stairs

Stairs are the part of a deck most likely to fail inspection, because the riser and tread dimensions are tightly controlled and easy to get wrong. The fix is to start from the total height and work backward to a legal riser.

The numbers that matter (IRC R311.7)

• Maximum riser height: 7¾". Minimum tread depth: 10".
• Every riser in a flight must be within 3/8" of the others — uniformity is strictly enforced.
• Minimum stair width: 36". Minimum headroom: 6'8".
• Four or more risers require a graspable handrail, 34–38" above the nosings.

Working out the layout

Take the total rise from the deck surface to the landing and divide by about 7.25" to get a starting riser count, then round so no riser exceeds 7¾". The number of treads is one less than the number of risers. At a 10–11" run per tread, that gives you the total horizontal run you need to reserve at the bottom of the deck.

Stringers

Cut stringers are usually 2x12, and there's a limit on how far they can span unsupported — long flights need a mid-span support or solid (uncut) stringers. Our deck stair calculator turns your deck height into a full riser-and-tread layout in one step.