stair design question

[donald girod]

A house we are building (Habitat project) has the following basement stair situation:

The total run of the stairs cannot exceed 115" because of headroom issues--the state code requires minimum headroom of 6'8"=80 inches, and there is a steel beam flange at 115" which is 85" above the floor. The total height of the stairs is 103.5". With 13 steps, the rise per step is

7.96". There are 12 treads, and 115/12 = 9.58" run per step. The building code requires at least a 10" tread, so stairs with 12 treads, a 7.96 rise and a 10" tread with about 1/2" nose would work (the nose of the bottom step would project slightly under the beam but nobody is going to care about this).

However, these dimensions violate the "two risers + 1 tread = 24 to 25" rule; you get 26, which is too large. My question: is a set of stairs with these dimensions going to be uncomfortable or unsafe to use? I know that 8" rise and 9" tread works just fine (that's what my stairs are), but I don't know how it would feel if the treads suddenly grew an inch.

[Wayne Whitney]

My understanding of the headroom requirement is that it is from the diagonal connecting the edges of the nosings, and hence part of the landing at the bottom of the steps has a greater headroom requirement than 80".

Which building code is this? CodeCheck West 2002 indicates that the

2000 IRC allows maximum 7.75" risers and minimum 10" treads, and the 1997 UBC allows maximum 8" risers and minimum 9" treads.

Cheers, Wayne

[Greg O]

I have a stairs to reach a storage area that are 9" run, 9" rise. I don't mind them at all. I did not sweat code because they are not a stairs the gets regular use. In your case I would cheat a bit on the over hang of the tread like you sugest. Your run is not 10" if you overhang the tread a 1/2", it is 9-1/2".

9-1/2" + 9-1/2" + 8" = 25-1/2". Close enough in my book when options are limited. The final answer will be your building inspector, if you have one. What does he say? Greg

[Colbyt]

Your degree of slope is high (38 degrees +-). But without getting the rise down to about 7- 7.5 you aren't going to correct that. Very few stairs in modern construction manage it.

That said, after a few trips up and down them most people adjust to the stairs as they exist. As long as the rise is 8" or less I think you will be fine for utility stairs. I would consider the wider tread an asset and I have small feet. What does the local code say about the rise?

Colbyt

[donald girod]

The New York code says the rise can be as large as 8.25 and the tread is to be at least 10 and should have a nose .75 to 1.25. I was thinking of cheating a bit on the nose; my main concern is that the tread is quite wide for stairs that are this steep. I don't know what the inspector says--I'll try calling him tomorrow. We want to do the stairs day after tomorrow.

[default]

I don't think so: Last I checked, you measured vertically from the edge of the nosing itself, at least in my ancient BOCA.

I don't understand why this issue is being addressed NOW anyway. Generally, you figure out how to put the stairs in BEFORE you build the house. Is this a rehab? In any case, a floor plan would be helpful, so we could rule out/suggest things like a raised or depressed landing at one end or the other, a switchback or L-shaped stairs, or going the other way.

To answer the question you actually asked, the stairs you seem to have in mind will be perfectly useable, it's just a question of whether your inspecter will pass them.

--Goedjn

[Wayne Whitney]

We agree on that, the question is what happens in front of the nosing of the very first step. My understanding is that you need some extra headroom here, since the diagonal connecting the nosings will take one additional tread depth before it hits the lower floor. This makes sense, since as you step on to the first step, you start to travel upwards before you even reach the first nosing.

Cheers, Wayne