IRC Stair & Guard Rules: Riser, Tread, Handrail, Guards

The requirement

Under the IRC, a riser can be at most 7¾ in (196 mm) tall. A tread must be at least 10 in (254 mm) deep. You need a handrail on any flight with 4 or more risers, set 34 to 38 in above the nosings. Guards must be at least 36 in high (R312). First check which edition your state and town adopted.

You can check all of these with a tape. The two numbers that shape every step are the riser and the tread (R311.7).

• Riser: how tall each step is. The cap is 7¾ in (196 mm). Go taller and the step is too big to climb safely. So you add a step to bring each one down. Every riser in a flight must be near equal. They can vary no more than 3/8 in top to bottom (R311.7.5.1).
• Tread depth (the going): how deep each step is. Measure it nosing to nosing, front edge to front edge. The minimum is 10 in (254 mm) (R311.7.5.2).

Three more numbers keep the stair safe to use:

Keep every step in a flight the same height and the same depth. The IRC only allows that tiny 3/8 in spread. One odd step is where people trip.

Guards & barriers

A guard is the barrier that stops a fall off an open edge. The IRC ties it to the height of the drop, not to the stair itself.

So if you can fall more than 30 in, you need a guard at least 36 in high. The gaps in it must be tight too. A 4 in sphere must not pass through any opening (R312.1.3). That keeps a small child’s head out. The open side of a stair gets a little more room, up to 4⅜ in. So does the triangle formed by the riser, tread and bottom rail, up to 6 in.

Work it out on site

Say your floor-to-floor height is 105 in. You want an even set of steps.

1. Pick how many risers. 105 ÷ 7¾ (the tallest a riser can be) = 13.5. You can’t have half a step, so round up to 14 risers. 105 ÷ 14 = 7.5 in per riser. That sits under the 7¾ limit. Good.
2. Set the tread. Use a 10 in tread or deeper, so it clears the minimum.
3. Check headroom and width. You need 6 ft 8 in of clear height above the pitch. You also need 36 in of clear width.

If 105 ÷ your riser count lands over 7¾, add a riser and divide again. Keep every step equal. These are example numbers. Plug your real floor-to-floor height into the calculator.

Do it in 5 seconds

Related

• The pillar: US building codes: the IRC, state by state. It shows how the model code gets adopted and amended. Check your local edition first.
• Building down under? See NCC stair requirements (Australia). The same stair rules for readers over there.

Sources

• IRC 2021, Section R311.7 — Stairways (riser, tread, headroom, width, handrail) and Section R312 — Guards (guard height, fall trigger, openings). Read the code at codes.iccsafe.org.
• Adoption & edition caveat — read this first. The IRC is a model code. It has no force until your state and/or town adopts it, almost always with local amendments. Editions in force are a patchwork — many places are still on IRC 2018 or 2015 — and California (CRC), Wisconsin, New York City and Chicago run their own codes. The figures above are the base IRC 2021 (stable across 2015–2024), but the enforceable number is the adopted-and-amended edition where you build. Confirm the edition and amendments with your local building department before you set out. Footing sizes (R403.1) are not listed here on purpose — they’re table-driven by your soil-bearing and loads, so read your soil/load table, don’t copy a number.