The state of New Jersey has specific building code mandates that cover how stairs are constructed, where they are required, and the dimensions they must adhere to. You must follow these stair code rules not only to obtain building permits, but also to provide the maximum amount of safety for those using the stairs.
The State of New Jersey bases its stair code for both commercial and residential construction on the International Building Code of 2009. This set of standards, which includes the International Residential Code (IRC), is revised every three years, so it is important to contact your local code agency for any updates or amendments that may be under review. All codes related to stair construction, covered by the 2009 IRC, are established and enforced by the Division of Codes and Standards.
The 2009 IRC, Section R311.7 requires a minimum clearance width of 36 inches in a stairway. This means that you must build in at least 3 feet of width for access in the area between the top of the handrail and the ceiling above. Clearance width on the stairs themselves must be at least 31 ½ inches when one handrail is installed and 27 inches where two handrails are installed. Available headroom within a stairway must be a minimum of 6 feet 8 inches, measured vertically from the front edge (nosing) of each tread and landing.
Treads and Risers
Section 311.7 of the 2009 IRC also covers stair tread and riser dimensions. The maximum riser height -- or the vertical area between each step (tread) in the stairway -- is 8 ½ inches, measured between the front edges of adjacent stairs. The minimum tread depth for foot placement is 9 inches between the front edges of adjacent stairs. The maximum allowance for slight differences in both riser heights and tread depths in a stairway is 3/8 of an inch. This means that the smallest riser height cannot be more than 3/8 of an inch less than the largest riser height, and the smallest tread depth cannot be more than 3/8 of an inch less than the largest tread depth.
Stairway Lighting and Storage
The New Jersey stair code also covers stairway lighting and any storage areas under a stairway you might include in your construction plan. Sections R303.6.1 and R311.7.8 require interior stairways to have a light located in each landing area that provides illumination on the center of landings and adjacent treads. A light switch on the wall must be provided on every floor that accesses stairways with six or more risers. Storage areas framed under stairways must have at least one layer of ½-inch gypsum board (drywall) on the walls and soffits of the enclosed space, under Section R302.7 of the 2009 IRC.