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The tread depth is 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 or stairway should not exceed the smallest by more than 3/8 inch (9.5 mm). The riser height is at most 7 and 3/4 inches (196 mm).
Some stair stringers may be sistered with 2x4-inch boards in order to strengthen a 2x10-inch stringer that has only 3-1/2 inches of board remaining beneath the tread-riser notch. An undersized stringer may also be over-spanned, of poor-quality wood, and may also have knots, cracks, or other defects that weaken the stringer board.
Each tread should have at least a 7 1⁄2 inch tread depth at 12 inches from the narrower edge. CA: For spiral stairs, all treads should have minimum run not less than 150 mm, and an average run not less than 200 mm.
Make sure the tread depth is at least 10 inches. For spiral stairs, all treads should be identical. Each tread should have at least a 7 ½ inch tread depth at 12 inches from the narrower edge. For winder stairs, treads should have a depth of at least 10 inches measured at a point 12 inches from the side where the treads are narrowest.
The throat depth is the net depth of a stringer once the steps are cut and removed, and it is measured from the step perpendicular to the bottom edge of the stringer. These tread and riser dimensions directly affect the size of the stringer board, the throat dimensions of a cut stringer, and the remaining amount of board remaining beneath the ...
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Stairway Rise and Run: The stairway riser height maximum is 7 and 3/4 inches (196 mm). That is measured vertically between the leading edges of the adjacent treads. The tread depth must be at least 10 inches (254 mm).
Stair stringers shall be made of 2"x 12" lumber at a minimum, and no less than 5 inches wide at any point. The image above depicts deck stair stringers. Stringers should be no more than 16 inches apart for wood treads, 12 inches for plastic composite.
Stair Guard Opening Limitations: According to the IRC®, the triangular opening at a guard at the open side of a stair formed by the riser, tread, and bottom rail of a guard must not allow a sphere 6 inches (153 mm) in diameter to pass through it.
Riser Height and Tread Depth: In commercial buildings, the height of risers must be between 4 inches and 7 inches, and the tread depth must be at least 11 inches for each step.