2008 NYS Stair Code: R311.5.3.1 says maximum rise of 8 1/4"
The above reference is from the
Residential code and you are not building a one and two family structure or a townhouse, thus the Residential code does not apply.
The following is from the 2010 New York State Building Code regarding risers and treads for stairways - which is applicable to structures other than one and two family or townhouses: (underlining and bold are mine)
- 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 sightline 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 Existing Building Code of New York State for the replacement of existing stairways.
I have an overall rise of 142 1/2"
I can use:
- 21 risers at 6 25/32" ea
- 20 risers at 7 1/8" ea
I would like to use
- 19 risers at 7 1/2" ea...with a 10" clear (11" overall) tread ....is that within code?
No, the above would not be within the code.
This would be the code compliant stair (riser/tread) layout: 142.5 inches / 7 inches MAXIMUM = 20.36 risers or 21 risers, which would be 142.5 inches / 21 risers = 6.78 inches or 6.75 inch (6-3/4 inch) risers for a overall height of 142.38 inches. That means you would need to make up 0.12 inches over the stairway, except that 0.375 inches is the tolerance between the shortest riser and the tallest riser, so just make the risers 6-3/4 inches and the difference at the first (lowest) or last (highest) riser would make up the difference and be within the allowed tolerance for risers.
The treads are required to be 11 inches MINIMUM and are measured as follows: "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"
That means the stair would have a landing at the bottom (the lower floor), a landing at the top (the higher floor) and the 21 risers would require 20 treads, thus the stairway would cover 20 treads X 11 inches = 220 inches from the top of the stair opening (top riser) to the bottom riser.
The above is showing the MAXIMUM riser height and the MINIMUM tread depth required to have for a compliant stair for the 142-1/2 inch floor-to-floor height.