What is the minimum width of residential steps?
First of all, I have a guide book to the code but not the actual code book. I have read the section on egress over and over, I have looked for answers on the net and as you can imagine it is up to how someone interprets the code. There is a lot on handdrail but nothing that says stair treads have to be a min. of 36″ which is what half of the people seem to think. The only reference to 36″ that I have seen is for above the handrail. That is not an issue for me. I need to know if I have treads between the timber stringers, can they be 32″? I need to do a 4 step landing at bottom turned 90 degs. and I need the extra 4″. Another question. In the code book guide i have the min. tread depth is 10″. But I have seen reference elsewhere under code 311.5.3.3 listed as 9″ min. I always went by 10″ but if i can do less then 10″ it would help. So, is it 10″?
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Replies
John,
Section R311.7.1 IRC 2009:
"Stairways shall not be less than 36 inches (914 mm) in clear width at all points above the permitted handrail height and below the required headroom height."
John,
When it comes to tread depth, the answer depends on which version of the code you have to follow.
2009 IRC: "R311.7.4.2 Tread depth. The minimum tread depth shall be 10 inches (254 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)."
2012 IRC: "1009.7.2 Riser height and tread depth. ... Rectangular tread depths shall be 11 inches (279 mm) minimum measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the tread’s nosing."
And your municipal office will have the code and can show you relevant sections. For any code question, the best bet is to check with the code enforcement officer - many of these items are up for some level of interpretation, so best to get the opinion of the person doing the interpreting.
Also, remember that there are two ways to measure tread depth - from face of riser to edge of nosing, or what is called "net tread depth" - from the edge of one step's nosing to a vertical line drawn from the next tread's nosing (that's what you actually "feel" going up the stairs, no matter how deep the overhang is).