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Sloped stair riser code9/29
So here is something I've never encountered before. A customer wants a staircase combining 1.5" thick slab treads, with a 1.25" nosing, with a sloped riser. The purpose in the design is to give the impression that the treads overhang the risers more than allowed by code. Here in Michigan I refer to the IRC 2009 code book, section R3184.108.40.206 which states that the tread nosing cannot be more than 1.25" (duh). But where it gets fuzzy to me is it goes on to say that the risers "shall be vertical or sloped under the tread above from the underside of nosing above at an angle not more than 30 degrees from the vertical." So does that mean the nosing overhang is determined by measuring from the furthest projection of the tread nosing to the point where the bottom of the tread meets the riser below? And if the riser below slopes or angles in from that point it does not add to the nosing distance?
The horizontal distance from face of top of one riser to the face of top of next riser determines the actual Run of the stair. Or, more simply face of nosing to face of nosing.
Just playing devil's advocate, why have a maximum nosing projection then? Wouldn't the logic behind a maximum nosing projection be that a riser is a barricade of sorts that keeps a foot from going too far under the next ascending tread, and that a nosing projecting too far, especially on a steeper staircase, is a toe snagging trip hazard?
I live in northern Michigan and our building dept. is alway happy to help with these issues. After all, they have to approve it in the end
Aaron, I don't know the answer to your question, but if the goal for the client is to have a larger tread for the foot, especially when descending on steeper slopes, sometimes an alternating tread can surely make it easier. Or even a modification of that, where the nose of the tread has a curving front, where the hump projects on every other step. ~ This means that you need to start on the right, as in proper foot each time, but it gives a larger tread for each foot to land on by getting the nosing of the one above out of the way.
Thanks Keith. That actually sounds like a cool maybe slightly organic design. But they arent looking for a wider tread, just a way to make the treads appear to float as much as possible with risers.