stair stringers

[bill1952]

I'm building a landing and short flight of stairs (6 R at 6.16", 5 T at 12"), all interior, and while I've built a lot of stairs, this is a little more on display. Visible open risers, thick (floating) treads, and intended to be a bit of a centerpiece. I thought I should confirm my design met code (NY 2020 based on 2018 IRC) but was surprised to find very little on the structural aspects. Not even a minimal throat dimension nor mention. Did I miss something? What is the IRC "prescribed" stringer design criteria for interior stairs? (40 psf is all I found.) What should a plan reviewer look for or an inspector measure?

FWIW My span is right around 48" so I was looking at a throat of 4" - 2 stringers each 3 to 4" thick.If I thought it was "bouncy" I could add another layer (1" cherry) on the stringers and inset 3 x 1/4 steel flitch plates.

Thanks.

 

[steveray]

What is the IRC "prescribed" stringer design criteria for interior stairs?

There are none...Hence they all need to be engineered.....

And you may have difficulty with those open risers...

 

[bill1952]

Thank you steveray for posting.

I'd be surprised if many stairs in house around here were designed by an rdp, though not everyone equates "engineered" as being designed (or sealed) by an rdp.

As far as open risers, I thought the 4" sphere rule was the test. 6.16" rise and treads thicker than 2.16" should do that. An inch nosing and tread depth greater than 11". Seems to say exactly that in 2018 R311.7.5.1 Am I missing something?

 

[BN4537]

IRC 2018 deck stair stringer spacing code?

I am working on some deck stairs and while I see a bunch of stuff online that says the max space between stringers is 18" I am not successful finding the relevant IRC 2018 section if any. My stairs are 6' wide made of 2x6 planks and wish to use 3 risers but not sure if up to code. Thanks

www.thebuildingcodeforum.com

 

[BN4537]

As far as open risers, I thought the 4" sphere rule was the test. 6.16" rise and treads thicker than 2.16" should do that. An inch nosing and tread depth greater than 11". Seems to say exactly that in 2018 R311.7.5.1 Am I missing something?

No, you are correct.

 

[bill1952]

Thank you, Beniah. I had found the 40 psf and planned to work with that with my not-an-rdp engineering. Just seemed like there should be more.

I'll just stand on middle tread with my wife as a load test before inspection.

 

[wwhitney]

Say we sister our cut stringers with graded 2x4s or 2x6s in the throat region. Is it then reasonable to apply IRC Table R802.4.1(5) for rafters with a 50 psf snow load to determine a lower bound for the maximum span of the sistered stringers with a 40 psf live load, taking into account only the sister?

If not, what is the difference in the beam bending checks for snow load vs live load?

Cheers, Wayne