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IRC stair rules
| Item | Requirement |
|---|---|
| Riser height | 7¾ in maximum |
| Tread depth | 10 in minimum |
| Variation within a flight | ⅜ in maximum |
| Headroom | 6 ft 8 in minimum |
| Clear width | 36 in minimum |
| Handrail height | 34–38 in above the nosings |
IRC R311.7, from the Des Moines and Winona handouts.
Common basement rises
| Total rise | Risers | Riser height | Total run at 10 in |
|---|---|---|---|
| 8′ 0″ | 13.0 | 7.38 in | 10′ 0″ |
| 8′ 4″ | 13.0 | 7.69 in | 10′ 0″ |
| 8′ 8″ | 14.0 | 7.43 in | 10′ 10″ |
| 9′ 0″ | 14.0 | 7.71 in | 10′ 10″ |
| 9′ 4″ | 15.0 | 7.47 in | 11′ 8″ |
| 9′ 8″ | 15.0 | 7.73 in | 11′ 8″ |
Many basements were built with stairs that predate the current code. Finishing the basement can trigger upgrades if the stair is altered, so ask your inspector before you change it.
Worked example
The example basement measures 7′ 8″ to the joists and 84 in to the bottom of the main beam. With ½ in drywall on the joists and ¾ in of new flooring, the ceiling finishes at 7′ 6.8″, comfortably over 7 ft. Under the beam the clearance is 6′ 11.2″, above the 6 ft 4 in allowed at obstructions. Switch to a 4 in drop ceiling and the room drops to 7′ 3.2″; still legal, with 3.25 in to spare. For the stairs, ¾ in of new flooring at the bottom shortens the bottom riser by the same amount, which can break the ⅜ in variation rule.
Where basement inspections usually fail
- Bedroom windows that are too small or too high, especially sliders and double-hungs measured by the frame instead of the opening.
- Window wells under 36 in deep from the wall, or deeper than 44 in with no ladder.
- Ceilings that dip under 6 ft 4 in at a duct or beam once drywall and flooring go in.
- Stairs with a short top or bottom riser after new flooring changes the floor levels.
- Missing fire blocking at the top of furred walls and around soffits.
Many cities publish one-page handouts on these items, like the St. Paul, Boise and Des Moines sheets cited on this site. Ask for your city's version before you frame.
Before you call for an inspection
- Measure every egress opening with the sash open and write the numbers on the frame.
- Measure ceiling height at the lowest duct or beam after the ceiling material is up.
- Check riser heights top and bottom after flooring.
- Leave insulation and vapor details visible until the insulation inspection if your town does one.
- Have the permit card and approved plans on site.
Common questions
How many steps for basement stairs?
Divide the total rise by 7.75 in and round up. A 104 in rise needs 14 risers of about 7.43 in.
What is the maximum riser height for basement stairs?
7¾ in under IRC R311.7, with no more than ⅜ in difference between the tallest and shortest riser.
Related calculators
Sources
- https://cms2.revize.com/revize/desmoines/document_center/Development%20Services/Permit%20Development%20Center/Residential/Residential-Stairs-Ramps-Handrails-2012-IRC-Rev-052014.pdf
- https://www.winonamn.gov/DocumentCenter/View/2175