ENGINEERING
Stairs
AWI References
Minimum Tread Thickness
"Per AWI, 3.2.1.3.a - Solid wood treads shall be a minimum of 3/4" thick."
Minimum Riser Thickness
"Per AWI, 3.2.2.2.a - Custom grade millwork risers shall be a minimum of 3/4" thick."
OSHA References
Vertical Clearance Standard Stairs
"Per OSHA, 1910.25(b)(2) - Vertical clearance above any stair tread to any overhead obstruction is at least 6'-8", as measured from the leading edge of the tread."
Uniformity Standard Stairs
"Per OSHA, 1910.25(b)(3) - Stairs have uniform riser heights and tread depths between landings."
Degree of Slope Standard Stairs
"Per OSHA, 1910.25(c)(1) - Stairs are installed at angles between 30 to 50 degrees from the horizontal."
Maximum Riser Height Standard Stairs
"Per OSHA, 1910.25(c)(2) - Stairs shall have a maximum riser height of 9-1/2"."
Minimum Tread Depth Standard Stairs
"Per OSHA, 1910.25(c)(3) - Stairs shall have a minimum tread depth of 9-1/2"."
Minimum Width Standard Stairs
"Per OSHA, 1910.25(c)(4) - Stairs shall have a minimum width of 22" between vertical barriers."
Maximum Riser Height Spiral Stairs
"Per OSHA, 1910.25(d)(3) - Spiral stairs shall have a minimum headroom above spiral stair treads of at least 6'-6", measured from the leading edge of the tread"
Vertical Clearance Spiral Stairs
"Per OSHA, 1910.25(d)(3) - Spiral stairs shall have a minimum headroom above spiral stair treads of at least 6'-6", measured from the leading edge of the tread"
Minimum Tread Depth Spiral Stairs
"Per OSHA, 1910.25(d)(4) - Spiral stairs shall have a minimum tread depth of 7-1/2", measured at a point 12" from the narrower edge."
Uniformity Spiral Stairs
"Per OSHA, 1910.25(d)(5) - Spiral stairs shall have a uniform tread size."
Typical Stair Dimensions
Solid Material
1/4" thick
Plywood Substrate Material
1/2" thick
Stair Anatomy
Anti Slip Insert
A hardware inserted into the tread of a staircase, generally near the nosing, to prevent stair related accidents. Can sometimes be decorative as well.
Handrail
A moulding used along a stairway, hallway, or corridor designed to be grasped by the hand to provide stability or support. Must meet local building codes.
Nosing
A rounded convex edge, as on a stair step.
Treads
The horizontal surface of a staircase step.
Riser
In stairwork, the board at the back of a tread that “rises” to the bottom of the next tread above. In an “open riser” stair, this element is left out, and the gap between the treads is open. Open riser stairs are prohibited by code in many circumstances.
Stringer
An inclined structural support for the treads and risers in a flight of stairs.
