Stairwells: Risers and Treads

[LindaDeavers]

My boss called and asked me the BOCA for step risers in Arlington County. I read him what it says in the Virginia Uniform Statewide Building Code (USBC) effective date September 15, 2000, 11. Change CABO subsection 314.2 to read . . . and in the Virginia Construction Code, Part I of the Virginia Uniform Statewide Building Code 2006 effective May 1, 2008, 13. Change Section R311.5.3.1 to read: R311.5.3.1 Riser Height and 14. Change Section R311.5.3.2 to read: R3115.3.2 Tread depth . . .

I hope these were the most recent. He was in a hurry and these were all I could find. He is giving a proposal for commercial stairwells. I made copies of both of these and put them in his in-box. Did I give him the right information? Please advise. Thank you.

[Jerry Peck - Codeman]

Hi Linda,

According to the Virginia Uniform Building Code available online your information is correct for residential stairways which would fall under that section.

The following is from the Virginia Uniform Building Code, Effective May 1, 2008, which is based on the ICC codes with the following changes: (underlining and bold are mine)
- 101.2 Incorporation by reference.
- - Note 1: The IBC references the whole family of International Codes including the following major codes:
- - Note 2: The International Residential Code is applicable to the construction of detached one- and two-family dwellings and townhouses as set out in Section 310.
- - - Add Section 310.6 to the IBC to read:
- - - - 310.6 Amendments to the IRC. The following changes shall be made to the IRC for its use as part of this code.
- - - - - 13. Change Section R311.5.3.1 to read:
- - - - - - R311.5.3.1 Riser height. The maximum riser height shall be 8-1/4 inches (210 mm). The riser shall be measured vertically between the leading edges of the adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm).
- - - - - 14. Change Section R311.5.3.2 to read:
- - - - - - R311.5.3.2 Tread depth. The minimum tread depth shall be 9 inches (229 mm). The tread depth shall be measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the tread’s leading edge. The greatest tread depth within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm). Winder treads shall have a minimum tread depth of 10 inches (254 mm) measured as above at a point 12 inches (305 mm) from the side where the treads are narrower. Winder treads shall have a minimum tread depth of 6 inches (152 mm) at any point. Within any flight of stairs, the greatest winder tread depth at the 12 inch (305 mm) walk line shall not exceed the smallest by more than 3/8 inch (9.5 mm).

Those changes make for a much steeper stair than that which is allowed in the IRC.

He is giving a proposal for commercial stairwells.

What you need are the requirements for commercial stairwells, i.e., other than dwellings covered by the IRC section.

From what I read in the Virginia Uniform Building Code, the IBC is included by reference:
- 101.2 Incorporation by reference. Chapters 2 – 35 of the 2006 International Building Code, published by the International Code Council, Inc., are adopted and incorporated by reference to be an enforceable part of the USBC. The term “IBC” means the 2006 International Building Code, published by the International Code Council, Inc. Any codes and standards referenced in the IBC are also considered to be part of the incorporation by reference, except that such codes and standards are used only to the prescribed extent of each such reference. In addition, any provisions of the appendices of the IBC specifically identified to be part of the USBC are also considered to be part of the incorporation by reference.
- - Note 1: The IBC references the whole family of International Codes including the following major codes:
- - - 2006 International Plumbing Code
- - - 2006 International Mechanical Code
- - - 2005 National Electrical Code
- - - 2006 International Fuel Gas Code
- - - 2006 International Energy Conservation Code
- - - 2006 International Residential Code
- - - Note 2: The International Residential Code is applicable to the construction of detached one- and two-family dwellings and townhouses as set out in Section 310.

With no amendments re-writing the section as stated in the ICC IBC, the sections as stated in the IBC would be applicable.

Thus, from the 2006 IBC, for commercial buildings, the following would be for stairways:
- 1009.3 Stair treads and risers. Stair riser heights shall be 7 inches (178 mm) maximum and 4 inches (102 mm) minimum. Stair tread depths shall be 11 inches (279 mm) minimum. The riser height shall be measured vertically between the leading edges of adjacent treads. The tread depth shall be measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the tread’s leading edge. Winder treads shall have a minimum tread depth of 11 inches (279 mm) measured at a right angle to the tread’s leading edge at a point 12 inches (305 mm) from the side where the treads are narrower and a minimum tread depth of 10 inches (254 mm).
- - Exceptions:
- - - 1. Alternating tread devices in accordance with Section 1009.9.
- - - 2. Spiral stairways in accordance with Section 1009.8.
- - - 3. Aisle stairs in assembly seating areas where the stair pitch or slope is set, for sight line reasons, by the slope of the adjacent seating area in accordance with Section 1025.11.2.
- - - 4. In Group R-3 occupancies; within dwelling units in Group R-2 occupancies; and in Group U occupancies that are accessory to a Group R-3 occupancy or accessory to individual dwelling units in Group R-2 occupancies; the maximum riser height shall be 7.75 inches (197 mm); the minimum tread depth shall be 10 inches (254 mm); the minimum winder tread depth at the walk line shall be 10 inches (254 mm); and the minimum winder tread depth shall be 6 inches (152 mm). A nosing not less than 0.75 inch (19.1 mm) but not more than 1.25 inches (32 mm) shall be provided on stairways with solid risers where the tread depth is less than 11 inches (279 mm).
- - - 5. See the Section 3403.4 for the replacement of existing stairways.

The layout and method used for the Virginia Uniform Building Code, incorporating the amended and changed sections in one document and the unamended and unchanged section in the referenced document make using the Virginia Uniform Building Code a bit awkward and not user friendly.

There is a big different in the requirements between riser heights and tread depths for dwelling units falling under the IRC and its revisions and the IBC sections which were not revised (at least not that I have found).

Dwelling requirements under the IRC amendments:
- R311.5.3.1 Riser height. The maximum riser height shall be 8-1/4 inches (210 mm).
- R311.5.3.2 Tread depth. The minimum tread depth shall be 9 inches (229 mm).

Commercial requirements under the IBC without amendments:
- 1009.3 Stair treads and risers. Stair riser heights shall be 7 inches (178 mm) maximum and 4 inches (102 mm) minimum. Stair tread depths shall be 11 inches (279 mm) minimum.