Note: This information refers to the Uniform Building Code, 1994 edition, except for items referring to the Americans with Disabilities Act (ADA). Check with your building department to determine which building code your area is using.
This applies to single family residences, individual units in Group R division 3 congregate residences, and guest rooms of Group R Division 1 Occupancies.
Rise and run: The important numbers here are a maximum rise of 8" and a minimum run of 9". A rise and run of about 7" by 10" is fairly typical, and is reasonably comfortable to use. Runs of over 10 1/2" will usually require three balusters per tread to comply with the 4" maximum opening in the balustrade.
Winder treads and circular stair treads: The code currently calls out a minimum run of 6" at the shortest end of the tread, and a 9" minimum run at a point 12" in from the edge. Having two or more treads come to a point to divide a square landing is not allowed.
Handrails: A continuous handrail is required the entire length of the run on any stair over 3 risers. This rail can stop at landings, but must be continuous at winder treads. The rail height is 36" minimum at level railings, and 34" to 38" above the front of the tread at rake rails.
Handrail size: This issue is covered under "Handrail size and gripping area".
Width: As a rule, the minimum width for a residentail stair is 36". If there is a high enough occupant load, it may be required to be wider. On large houses, your architect should check to verify the required width.
Rise and run: Stairs in commercial buildings need to have maximum rise of 7", and a minimum run of 11". A rise of less than 6" is really a little too low, and runs longer than about 13" are not comfortable with a normal stride.
Circle stairs: The shortest side of the stair must have a run of no less than 10", and the radius of the inside of the stair must be no less than twice the width of the stair. In practice, this means the minimum inside radius for a commercial stair is about 8 feet.
Handrails: See ADA compliance.
Width: Required width varies with occupant load, and must be figured for the appropriate use. The standard minimum is 44", with an exception for an occupant load of 49 or less allowing a 36" minimum. A greater width will be required for larger occupant loads. See section 1003.2 of the UBC to calculate the required width.
Handrails: The ADA requires continuous handrail from the bottom riser to the top riser, and extensions at the top and bottom. At the bottom, the rail must continue past the bottom riser on the rake for 1 run, then level out for 12". At the top, it must level out and continue for 12" past the top riser. If there is a corner at the top or bottom, the rail should continue around the corner to provide the required distance. The handrail's grip should be no wider than 1 1/2".
Uses: Spiral stairs have significant limitations on their use under the UBC. As the primary access, they can only serve an area of less than 400 square feet. As a secondary stair, they are quite acceptable.
Layout: A typical code compliant wood stair has a minimum width of 26" between the center pole and the inside of the handrail. With a 6" center pole and a 2 1/2" wide handrail, that makes a minimum diameter of 63". With an allowance for finger room, a minimum opening of 67" is typically required. (Metal spiral stairs can be slightly smaller in diameter, as the pole and handrail can both be smaller). 12 treads make a complete circle in a standard layout. Normal rises range from 8 7/8" to 9 1/2" maximum for a stair with a 1/4 circle landing. If the landing is reduced in size, slightly smaller rises are possible. Therefore, the total rise determines where the top and bottom risers are in relation to each other.
Residential stairs: This issue is a problem, as almost every building department, and every inspector in each department, has their own criteria on how wide the grip can be. The UBC wording says: "The handgrip portion of handrails shall not be less than 1 1/4" (32mm) inches nor more than 2 inches (51mm) in cross sectional dimension or the shape shall provide equivalent gripping surface" (Emphasis ours). Since "equivalent gripping surface" is not defined, it is up to every inspector to interpret it. Our recommendation is to show a sample of your rail to your inspector if the grip is more than 2" wide, and ask if he'll accept it.
Commercial stairs: The rule for commercial rails is to follow ADA requirements, which say the grip can be no wider than 1 1/2". Some areas are not strict about enforcing this, but from a legal standpoint you should follow the federal standards.
Commercial: Guardrails are to have a minimum height of 42". Handrails are to e between 34" and 38" above the nosing of the tread, measured plumb. On the stair itself, the handrail height can also be used for the guardrail height, but this does not apply to the landings.
Residential: Level guardrails have an exemption from the 42" commercial requirement, allowing a minimum height of 36". Handrails are to be between 34" and 38" above the nosing of the tread, measured plumb.
While it is intuitively obvious that steeper stairs should be more dangerous, there is no scientific evidence to this effect. There is good evidence that very shallow stairs (less than 6" (150 mm) rise and more than 14" (350 mm) runs) do present a tripping hazard. It is also clearly true that irregular rises or runs are hazardous.
This table is based on our experience. It is intended to be a guide to reasonable and comfortable stairs. Generally, stairs with a larger rise should have shorter treads and vice versa. The three traditional formulas for a comfortable stair all produce similar ratios between the rise and the run.
All of the model building codes regulate rise and run. Check with your local building department for the current rules in your area.
| Type of Stair | Suggested Rise | Suggested Run |
| Spiral stair* | 8 3/4" to 9 1/2" (225 to 245 mm) | 12 treads equal a full circle. |
| Circular stair | Per use of stair. (This table) | Per use of stair. Run measured 12" (305 mm) from the center of the inside handrail. |
| Unoccupied basement or attic | 8" (205 mm) (Or ladder**) | 9" (230 mm) |
| Small house or secondary stair in a large house | 7 1/2" (190 mm) | 10" (255 mm) |
| Large house main stair | 7" (180 mm) | 11" (280 mm) |
| Public stair | 6" to 7" (150 to 180 mm) | 11" to 13" (280 to 330 mm) |
* A spiral stair has treads projecting from a support pole. The geometry of a spiral stair is effected by the size of the of the central column and the width of the stair. This guide assumes a pole diameter of 4" to 8" (100 to 200 mm.) The extreme rise is necessary to provide headroom under the landing. A landing panel thickness of 2" (50 mm) or less is also required.
** A ladder, which is essentially a very steep stair, may be appropriate access for storage or equipment spaces which are visited infrequently.