Guides / Decks and patios · Updated
Deck railing height and stair code
From the 2021 IRC, sections R312 and R311.7, and the American Wood Council deck guide. Towns can amend the code, so the building department has the final say.
Short answer
36 in from the deck boards to the top of the rail on a house deck. You need it once any part of the deck is more than 30 in above the ground. Commercial decks and apartment balconies under the commercial code go to 42 in.
When you need a railing
The code calls it a guard. You need one where the deck surface is more than 30 in above the grade below it, measured anywhere within 36 in out from the edge. So a low deck on a slope can need a guard on the downhill side and not the uphill side.
Under 30 in, the code doesn't make you put one on. You still can.
Heights
| Where | Height | Measured from |
|---|---|---|
| House deck guard | 36 in min | Deck surface |
| Commercial deck guard (IBC) | 42 in min | Deck surface |
| Guard along the stairs | 34 in min | Line along the stair nosings |
| Stair handrail | 34 to 38 in | Line along the stair nosings |
| Guard that doubles as the stair handrail | 34 to 38 in | Line along the stair nosings |
The 36 in is a minimum. A 42 in rail is legal on a house deck, and plenty of people build them on high decks.
Gaps between balusters
A 4 in ball can't pass through anywhere in the guard. Up the stairs it loosens to 4 3/8 in. The triangle under the bottom rail, where the tread and riser meet, can pass 6 in.
Measure your baluster gap with the balusters in hand. A 2x2 is really 1 1/2 in, so on center spacing comes out to 5 1/2 in at most.
Stair handrails
Four risers or more needs a handrail on at least one side. It sits 34 to 38 in above the nosings and has to be graspable. A round rail runs 1 1/4 to 2 in across. A flat 2x6 cap is not a handrail.
Posts
The American Wood Council deck guide spaces guard posts 6 ft apart at most. A guard has to hold 200 lb pushed on the top rail, and a post screwed to the outside of the rim won't. Bolt it through and block it like the guide shows.
Stairs
| Width | 36 in clear, minimum |
|---|---|
| Riser | 7.75 in max. No two risers in a flight more than 3/8 in apart |
| Tread | 10 in deep, minimum. No two more than 3/8 in apart |
| Nosing | 3/4 to 1 1/4 in. Not needed when treads are 11 in or deeper |
| Headroom | 6 ft 8 in |
| Tallest flight | 12 ft 7 in of rise, then a landing |
| Landing | Top and bottom, at least 36 in deep and as wide as the stairs |
Stringers
| Spacing | 18 in on center |
|---|---|
| How many | 3 at least |
| Span | 6 ft max for cut stringers between supports |
| Stock | 2x12, with at least 5 in left behind the cuts |
Lay the stairs out for your deck height with the stair calculator.