Stair code requirements
The rules come from section R311.7.5 of the International Residential Code as states and cities adopt it. Below is the wording in published government copies, with the edition each copy states.
On this page
Stair rules control riser height (the vertical step), tread depth (the horizontal step), how much risers and treads may vary within one flight, stair width, headroom and handrails. Uneven steps are a leading cause of falls, which is why the code limits the difference between the largest and smallest riser in a flight.
States and cities amend these numbers more than most code sections, so the copies below differ. Before you build stairs for a deck, basement or addition, use the edition your city enforces (on its city page) and ask the department if your design is close to a limit.
The International Residential Code (IRC) is a model code. It is law only where a state or city adopts it, usually with changes, so the wording below shows how the model reads in published government copies, not the rule where you live.
Boise, ID
handout dated February 2022
- 7.75 inches.
R311.7.5.1 Risers: The riser height shall be not more than 7 ¾ inches (196 mm).
1 - 10 inches.
R311.7.5.2 Treads: The tread depth shall be not less than 10 inches (254 mm).
1 - 0.375 inches.
The greatest riser height within any flight of stairs shall not exceed the smallest by more than 3/8 inches (9.5 mm).
1
Connecticut (statewide)
2022 CSBC amendments to the 2021 IRC
- 8.25 inches.
(Amd) R311.7.5.1 Risers. The riser height shall be not more than 8¼ inches (209.5 mm).
2 - 9 inches.
(Amd) R311.7.5.2 Treads. The minimum tread depth shall be 9 inches (229 mm).
2
Sources
- IRC Code Handout #437 Stair Treads & RisersCity of Boise, ID, Planning & Development ServicesPublished February 2022Checked November 7, 2026
- 2022 Connecticut State Building Code (w/ Errata #1)State of Connecticut, Department of Administrative Services, Office of the State Building InspectorEffective October 1, 2022Checked November 7, 2026