Calculate Open Staircase code compliance

4 Replies

I have an open staircase with mono-stringer and thick wood treads going in my new build. My architect provided some treads on the drawing which I took as gospel, now that I am ordering I am trying to verify everything meets code and it's a PITA. 

Everything comes in to meet codes using this calculator with specs below, except I don't know the above floors headroom yet, but I am confused by the total run of 202". I have a measured opening in the floor of 134". I'm sure the stringer could mount to the floor farther out, until the headroom is not met, but I think 60" over the floor opening is ridiculous. 

My floor system is 1.5" and ceiling height is 10', so 11.5' total. I have to go on site to measure the overhang distance still. 

The treads I was buying were 3" thick wood treads, but I realize I cannot meet the 4" sphere requirement. The min tread height is 7 1/8" - 7.75" so I used 7.5" rise height with a 3.5" thick tread.

Calling all experts so I order the right thing!

@Leland Smith you need 80” clear from the top of the tread to the ceiling. If you don’t have it you can slope part of the ceiling. Doesn’t look great but it’s an option. The other option is to move the stair slightly but I don’t know if that works with your floor layout. Everything with the stair itself looks fine and good catch on the thicker treads.

@Eric Teran Thanks. I pulled the dwg up in Autocad online to see what my architects assumptions were. It appears he used a 4"x11" tread. I think that was my original plan and looks like I'm stuck with that to meet code unless I add some blocking bar between treads. The actual tread measures 11.25" run which adds to the run of the staircase, according to the calculator about 4". I might be one step off from getting the 80" clearance as the floor opening is only 134", so it's coming right to the edge of the tread that violates. I don't know why the architect designed it so close. Also, the opening of the staircase underneath is 134" but this website is calculating 176" to the base of the stringer which means the staircase will oddly have dead floor space under it. The framing has a short truss at the head of each staircase opening so I can't slant the headroom. It is very tight as it is. The truss is supporting the staircase above so it can't move either. I may have to see if the tread manufacturer can give me an 11" depth tread. 

@Eric Teran . Using the truss drawings I did verify the measurement of the opening for staircases is 135" for that level (posted on the other thread). 

I think I was using that calculator in error assuming that the nosing was part of the run length, but it doesn't appear to be based on the fact that overall run does not change. In that case, if I use the maximum code limit of 3/4 "nosing" or in this case tread overlap, I get a 10.5 equivalent "run" on their stringer calculator. This brings me just under the 135" floor opening calculation early on the 5th tread (so some headroom as you step down). This makes me feel a bit better, but I had better get shop drawings from the metal guy doing the stringer to ensure all these are dialed in. I have no drawings to date of the stringer design.