NYS Commercial Stair Code: Risers and Treads

[stubing]

Hello
I am designing a metal stair for a commercial application in an 150 year old warehouse.
I would like it be code compliant for general use as a main stair for a 6000sq ft 2nd fl.

I have always used a 7 1/2" riser and 10" tread (Rise x Tread = 75)

2007 NYS Stair Code: 1009.3 Stair treads and risers requires 7" rise and 11" tread
2008 NYS Stair Code: R311.5.3.1 says maximum rise of 8 1/4"

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?

Thanks
SV in Kingston NY

[Jerry Peck - Codeman]

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.

[stubing]

Code Man
Thanks for clearing that up, I am on track with the 21 risers.
I might be second guessing myself with the requirement for a mid-way landing
I am operating under the rule: less than a 12' overall rise doesn't not require a landing to break a rolling fall.
Is there a requirement that my staire with a 142 1/2" rise would need a landing?

Thanks

[Jerry Peck - Codeman]

I am operating under the rule: less than a 12' overall rise doesn't not require a landing to break a rolling fall.
Is there a requirement that my staire with a 142 1/2" rise would need a landing?

You are within the allowable overall height which does not *require* an intermediate landing, but remember, codes are *minimum* safety standards and installing an intermediate landing with an overall height which is only 1-1/2" less than the maximum height would certainly be treated as a "good idea".

Keep in mind that adding the intermediate landing also makes the stair longer overall with regards to the floor space it will take up. I.e., increased safety comes with a trade-off of losing floor space equivalent to the length of the landing (which must be as long in the direction of travel as the stair is wide, and the minimum width of the stair would be 44" plus - 44" is the minimum width, the "plus" is that the width may need to be wider based on number of occupants if the calculations come out that way).