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Residential Stair Design – Guidelines, Criteria and Dimensions

Sean O'Hara — Tue, 11 Oct 2011 07:49:28 +0000

I received a question about stair width from one of our clients and thought it made sense to clarify the typical stair design rules for houses. These are the rules that are in the 2006 International Residential Code.

Stairways have to be at least 36" clear width above the handrail height. Handrails can't project more than 4.5" into each side.

You need at least 80" of head height throughout the stair.

The maximum height of a riser is 7.75" and the treads have to be at least 10" deep. Treads also need to be a minimum of 4" tall.

If you have winders they can't be shallower than 6" and they have to be at least 10" deep when you're 12" into the winder.

The landings must be at least as deep as the stairs are wide and you can't go up more than 12' without a landing.

Handrails have to be mounted between 34" and 38" above the tread nosing and must run the full length of the stairs. The handrails have to be at least 1.5" off the wall and where they are circular they need to be 1.25" to 2" in diameter. If the handrail isn't circular it needs to have a perimeter between 4" and 6.25" with a maximum cross section of 2.25".

There are a number of other rules for particular situations but these are the general guidelines. There are more difficult stair and handrail rules for commercial and multifamily dwellings. I've also written a separate post for spiral stairs.

Originally posted 2008-09-29 17:01:01.

Residential Spiral Stairs – Guidelines, Criteria and Dimensions

Sean O'Hara — Fri, 24 Oct 2008 18:41:25 +0000

Spiral staircases may be an option for your residential applications where you can't fit a conventional staircase. These are the rules from the 2006 International Residential Code.

Spiral staircases have to be at least 26" wide with each tread being at least 7.5" deep when you're 12" in from the narrow end. The treads have to have identical (uniform) dimensions and a rise of no more than 9.5". You also have to provide a headroom of at least 6'-6".

You can use spiral staircases in limited commercial applications where the space it serves is no more than 250 square feet and doesn't serve more than 5 occupants. You can also use spiral staircases to access theater galleries, catwalks and gridirons. Beyond that spiral staircases are for residential use only.

The trick with spiral stairs is coming up with a combination of these dimensions that ends up facing the right direction at the top and bottom of the stair. Just because the rise and run work out doesn't mean that the direction will work out. You can go as steep as 9 risers per turn but you'll likely need to ease that to help you end up pointing the right direction. If you are creating a stair with more than 10 risers per turn you'll need to start increasing the diameter of the stair where you'll have the minimum tread depth.

You should also read the typical residential guidelines for more conventional stairs.

Commercial Stair Design – Guidelines, Criteria and Dimensions

Sean O'Hara — Tue, 21 Oct 2008 07:54:41 +0000

After seeing the popularity of my post on Residential Stair Design, I thought it made sense to explain the guidelines from the 2006 International Building Code for commercial buildings and common stairs in buildings with more than two dwelling units. It is much more complex and there are some exceptions if you need them so please contact me if you need help. These are the general rules.

Stairways have to be at least 44" if you have an occupant load over 50 (and may be more if your occupant load is large). If under 50 occupants you can go to 36" width. There are other exceptions for spiral stairs, aisle stairs and incline stairs but these types will have to be covered in a later post.

You need at least 80" of head height measured off the tread nosings and it needs to be maintained for one additional riser depth at the bottom of the stairs.

The riser height must be between 4" and 7" and the treads must be at least 11" deep.

If you have winders they need to be at least 11" deep when you're 12" in from the narrow edge and the minimum depth must be 10". You can't use winders in required stairways unless they are within a dwelling unit.

The landings must be at least as deep as the stairs are wide (up to 4'-0") and you can’t go up more than 12′-0" vertically without a landing. Where a door opens into the landing it can't project more than 7" into the required depth of the landing.

Handrails must be mounted between 34" and 38" above the tread nosings and landings. Where they are circular they need to be 1.25″ to 2″ in diameter. If the handrail isn't circular it needs to have a perimeter between 4" and 6.25" with a maximum cross section of 2.25". The handrail needs to be mounted a minimum of 1.5" off the wall.

Handrails in IBC buildings need to return to a wall, a guard or the walking surface or continue to another handrail. The IBC requires that your handrail extend 12" past the top riser and one tread depth past the bottom riser. It important to note that the ADA will require you to go one tread depth plus 12" past the bottom riser so it generally overrides the IBC.

Your handrails need to be on both sides of the stair and can't project more than 4.5" into the stair width on each side. On a very wide stair you need to space intermediate handrails no more than 60" apart.

Most commercial buildings will also require the ramp design guidelines.

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