How to Calculate Tread & Rise for Stairs

The requirements for the minimum depth of tread and maximum rise of steps for residential stairs are specified in the 1997 Standard Building Code (SBC) and the 1997 Uniform Building Code (UBC), which have been adopted as the local building codes by almost all communities across the country. Additional local restrictions may have been added to the conditions and requirements of the code as well.

Things You'll Need

• Calculator

Instructions

1. Determine the minimum tread depth required by your local building code. The minimum tread depth for residential stairs required by the 1997 SBC and the 1997 UBC is 9 inches and by the International Residential Code, 10 inches. Your local city or county Planning Office can tell you which code is used in your location.

2. Determine the maximum rise required by your local building code. The maximum rise restriction for residential stairs required by the 1997 SBC and the 1997 UBC is 8 inches, and by the International Residential Code, 7 1/4 inches.

3. Calculate the number of steps required to go from the floor to the top of the stairs. If the total rise of the stairs is 8 1/2 feet and the maximum rise permitted by code is 8 inches, or 0.66 foot, divide the total rise of the stairs by the rise permitted by code: 8.5 / 0.66 = 12 steps required to go from the floor to the top of the stairs.

4. Calculate the length of the floor space required for the stairs. If the minimum tread depth required by code is 9 inches, or 0.75 foot, and 12 steps are required to go from the floor to the top of the stairs, multiply the minimum tread depth permitted by code by the number of steps required by the building code: 0.75 x 12 = 9 feet of linear floor space required for the stairs.

Tips & Warnings

• Ask your local Code Enforcement Office if there are restrictions on the minimum stair width, as well as on tread and riser height.

References

• Architectural Graphic Standards for Residential Construction; Janet Rumbarger, AIA; 2003

Resources

• Construction Codes and Inspection Handbook