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    Risers and Tread Dimensions

    Risers and Tread Dimensions

    New postby zeppieri on Thu Oct 21, 2010 9:28 am

    I am having difficulty finding a definitive answer to the following issue and even my architect seems confused. I am in the process of building a new home in Nassau County (NY), Town of North Hempstead. I have a sliding glass door leading to a backyard patio. It is 26" from top of finished floor to top of patio (approx 27" from top of door sill to patio). My architect is telling me that there is a formula between riser height and tread depth. We are looking to do a 6 1/2" step down out of the sliding door to a 3' landing, then three 6 1/2" risers. The architect says that the treads can be no more than 11 1/2" and he referred me to new york state building code 311.5.3.2. But when I look at that section I don't see any type of formula. It merely requires risers to be less than 8 1/4" and treads to be no less than 9". I found nothing in the local building code on this issue. I was trying to avoid a handrail but I believe we will need one with 3 risers.

    So, my questions are:

    Will it be code compliant to have three 6 1/2" risers and a 6 1/2" step out from the door (actually 7 1/2" from top of door sill to landing)?

    Can I have treads of at least 12" with those 6 1/2" risers?

    Is there any type of formula between risers and treads that I need to comply with?

    Would a handrail be necessary with 3 risers if the total height from patio to landing is less than 2'?

    Your attention and consideration of these questions is greatly appreciated. Thank You
    zeppieri
     
    Posts: 2
    Joined: Wed Oct 20, 2010 9:50 am

    Re: Risers and Tread Dimensions

    New postby Jerry Peck - Codeman on Thu Oct 21, 2010 9:16 pm

    First, some questions, then some background information, followed by more questions and information (not necessarily in that order, I guess).

    Your architect is citing the New York State Building Code instead of the New York State Residential Code - do you know why? I am presuming the questions are regarding a single family house or a townhouse, if this is regarding a condo or a co-op, then the building code would apply, however the dwelling unit requirements would apply to "within" the dwelling unit and not the other requirements for 'other than dwelling units'.

    The NYS Residential Code states:
    - R311.5.3 Stair treads and risers.
    - - R311.5.3.1 Riser height. The maximum riser height shall be 8 1/4 inches (209 mm). The riser shall be measured vertically between leading edges of the adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm).
    - - R311.5.3.2 Tread depth. The minimum tread depth shall be 9 inches (229 mm). 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. The greatest tread depth within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm). Winder treads shall have a minimum tread depth of 10 inches (254 mm) measured as above at a point 12 inches (305) mm from the side where the treads are narrower. Winder treads shall have a minimum tread depth of 6 inches (152 mm) at any point. Within any flight of stairs, the greatest winder tread depth at the 12 inch (305 mm) walk line shall not exceed the smallest by more than 3/8 inch (9.5 mm).
    - - R311.5.3.3 Profile. The radius of curvature at the leading edge of the tread shall be no greater than 9/16 inch (14.3 mm). A nosing not less than 3/4 inch (19 mm) but not more than 1 1/4 inch (32 mm) shall be provided on stairways with solid risers. The greatest nosing projection shall not exceed the smallest nosing projection by more than 3/8 inch (9.5 mm) between two stories, including the nosing at the level of floors and landings. Beveling of nosing shall not exceed 1/2 inch (12.7 mm). Risers shall be vertical or sloped from the underside of the leading edge of the tread above at an angle not more than 30 (0.51 rad) degrees from the vertical. Open risers are permitted, provided that the opening between treads does not permit the passage of a 4-inch diameter (102 mm) sphere.
    - - - Exceptions:
    - - - - 1. A nosing is not required where the tread depth is a minimum of 11 inches (279 mm).
    - - - - 2. The opening between adjacent treads is not limited on stairs with a total rise of 30 inches (762 mm) or less.
    - R311.5.4 Landings for stairways. There shall be a floor or landing at the top and bottom of each stairway.
    - - Exception: A floor or landing is not required at the top of an interior flight of stairs, provided a door does not swing over the stairs.
    - - A flight of stairs shall not have a vertical rise greater than 12 feet (3658 mm) between floor levels or landings.
    - - The width of each landing shall not be less than the stairway served. Every landing shall have a minimum dimension of 36 inches (914 mm) measured in the direction of travel.
    - R311.5.5 Stairway walking surface. The walking surface of treads and landings of stairways shall be sloped no steeper than one unit vertical in 48 inches horizontal (2-percent slope).
    - R311.5.6 Handrails. Handrails shall be provided on at least one side of each continuous run of treads or flight with four or more risers.

    Some background from older codes: Stairways for residential dwellings used to have a formula applied to their design to limit their slope from being too high, limit the height of the risers, and require a minimum depth for the tread. That formula used to be "Two risers plus one tread equals between 24 and 25", combine that with the maximum riser height (which varied by state, many states were 7-3/4", some were 8", and some - like NY - were 8-1/4") combined further with a tread depth (which also varied by state, many states allowed a minimum tread depth of 9" but required a 1" nosing for tread depths less than 10") would all calculate out to a 'reasonable' slope stairway.

    Here is an example: A stair has risers which are 8" and a tread of 9", that would calculate out as 8+8+9=25. That would be the steepest allowed slope because if the riser heights were the allowed 8-1/4" the total would be 25-1/2 with the minimum tread. Likewise, the opposite would be a stair with a riser height of 6" and a tread of 12", for 6+6+12=24. The latter example *would* fall within the allowed "two risers plus one tread equals between 24 and 25", however, that formula was not really designed to control less steeply sloped stairs, it was designed to control and limit the steeper sloped stairs.

    That "two risers plus one tread equals between 24 and 25" went out some time ago, it was replaced with what was really being addressed: maximum riser height and minimum tread depth. There is nothing wrong with a very shallow stair (other than taking up A LOT of floor space, which cost extra money).

    Thus we now get back to the NYS Residential Code requirements:
    The NYS Residential Code states:
    - R311.5.3 Stair treads and risers.
    - - R311.5.3.1 Riser height. The maximum riser height shall be 8 1/4 inches (209 mm). The riser shall be measured vertically between leading edges of the adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm).

    As you can see, there is no "minimum" riser height for residential dwelling units. However, keep in mind that there is a minimum riser height for stairs in other than dwelling units, and stairs in other than dwelling units are held to a higher standard, so that minimum riser height also serves as a good safety minimum for dwelling units - the minimum riser height for other than dwelling unit stairs is 4". Less than 4" is considered to becoming a trip hazard and it upsets the standard gait for which most people use on stairways.

    There IS, however, a maximum riser height which must be met: not greater than 8-1/4" riser height.

    There IS also a minimum tread depth requirement of 9", however, a 1" nosing is required if the tread depth is less than 11" (the nosing is actually allowed to be between 3/4" and 1-1/4", the 1" is the "typical" and the "intended" average as can be seen in the nosing profile and limitations on nosing variations) :
    - - R311.5.3.2 Tread depth. The minimum tread depth shall be 9 inches (229 mm). 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. The greatest tread depth within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm). Winder treads shall have a minimum tread depth of 10 inches (254 mm) measured as above at a point 12 inches (305) mm from the side where the treads are narrower. Winder treads shall have a minimum tread depth of 6 inches (152 mm) at any point. Within any flight of stairs, the greatest winder tread depth at the 12 inch (305 mm) walk line shall not exceed the smallest by more than 3/8 inch (9.5 mm).
    - - R311.5.3.3 Profile. The radius of curvature at the leading edge of the tread shall be no greater than 9/16 inch (14.3 mm). A nosing not less than 3/4 inch (19 mm) but not more than 1 1/4 inch (32 mm) shall be provided on stairways with solid risers. The greatest nosing projection shall not exceed the smallest nosing projection by more than 3/8 inch (9.5 mm) between two stories, including the nosing at the level of floors and landings. Beveling of nosing shall not exceed 1/2 inch (12.7 mm). Risers shall be vertical or sloped from the underside of the leading edge of the tread above at an angle not more than 30 (0.51 rad) degrees from the vertical. Open risers are permitted, provided that the opening between treads does not permit the passage of a 4-inch diameter (102 mm) sphere.
    - - - Exceptions:
    - - - - 1. A nosing is not required where the tread depth is a minimum of 11 inches (279 mm).
    - - - - 2. The opening between adjacent treads is not limited on stairs with a total rise of 30 inches (762 mm) or less.

    Okay ... you now have a MAXIMUM (only) riser height and a MINIMUM (only) tread depth.

    For handrails, though, the requirement is shown as:
    - R311.5.6 Handrails. Handrails shall be provided on at least one side of each continuous run of treads or flight with four or more risers.

    You could take your 26" total rise, divide by 4 (3 risers will exceed the maximum riser height) and get 6-1/2" for riser height. You will have 4 risers, which means you will need to install a handrail.

    I am curious ... why would you NOT want a handrail? Handrails are safety features and stairs are inherently unsafe.
    Jerry Peck - CodeMan
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    Re: Risers and Tread Dimensions

    New postby zeppieri on Fri Oct 22, 2010 12:38 pm

    Thank you for your response. Some additional thoughts/info/questions:

    - it is a single family home

    - the reason I was looking to avoid a handrail is merely asthetics but I understand the safety aspects.

    - the code mentions that 4 risers requires a handrail. I will have 3 risers from the landing to the patio. The 4th "riser" is from the landing up to the door. So is that considered 4 risers for the handrail to be required?

    - I'm not sure why the architect cited the Building Code (maybe he said the Residential code and I misunderstood?)

    - so it sounds like the formula he was referring to is some rule of thumb architects use and not really a requirement? or perhaps it applies to interior steps only?

    Again, thank you for your input
    zeppieri
     
    Posts: 2
    Joined: Wed Oct 20, 2010 9:50 am

    Re: Risers and Tread Dimensions

    New postby Jerry Peck - Codeman on Fri Oct 22, 2010 8:04 pm

    zeppieri wrote:- it is a single family home

    That is what I thought, and that would be the residential code.

    - the reason I was looking to avoid a handrail is merely asthetics but I understand the safety aspects.

    - the code mentions that 4 risers requires a handrail. I will have 3 risers from the landing to the patio. The 4th "riser" is from the landing up to the door. So is that considered 4 risers for the handrail to be required?


    The code says: R311.5.6 Handrails. Handrails shall be provided on at least one side of each continuous run of treads or flight with four or more risers.

    Which is frequently interpreted as being 3 risers not interpreted by a landing, and, legally and code-wise, is correct, however, the code is a minimum life safety document, and to interpret that to its minimum potential is lowering the standard as much as would possibly be legally allowed - until someone falls and the homeowner (you) and their insurance company (your insurance company) is sued, resulting in dollars changing hands because someone was injured on your stairway. "Legally" you would have met code, minimally, however, the code also gave you a chance to exceed that minimum (just like exceeding the 9" tread depth and being shorter than the 8-1/4" riser height) and you would have elected to not exceed the minimum, and any jury would likely reward the unsuspecting person (unsuspecting that your stairway was as minimum as allowed) who was injured. The law guides juries, but juries tend to lean toward the innocent party.

    - so it sounds like the formula he was referring to is some rule of thumb architects use and not really a requirement? or perhaps it applies to interior steps only?


    That formula used to be more than 'rule of thumb', it used to be 'the code', with "used to be" being the key part of that phrase - that formula no longer applies. Some architects are slow in accepting changes like that.
    Jerry Peck - CodeMan
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