Stair Stringers

[Dennis Putnam]

I have an opening for stairs in a storage shed (20X17) framed with 2X12 joists and Simpson joist hangers that is 38" wide and 9' high. I want to add my stair stringers (3) but the Simpson sites' hanger drawing shows a maximum of 12" to a support frame. I would like to keep the space under the stairs clear for storage. One stringer is against a wall that will be supported by the wall framing. It is the other 2 stringers that concern me. Is it really necessary to provide vertical supports for those stringers or is that perhaps overkill? Thanks.

[Bill Graham]

9' rise will get you 15 risers@ 7-3/16", 14 treads @ 10". You'll need most of a 16' 2x12 for the stringers and they'll flex over that length if supported only at the ends.

You could try nailing a full-length 2x4 or 2x6(preferably yellow pine or Doug fir depending on where you are) to the inside of the stringer and see if you're happy with the results. If it's still bouncy you'll need to add some mid-span support. It all depends on what you're willing to tolerate in the feel.

The last 3-4' of run under the stairs is essentially useless for storage anyway, you could build a small knee wall there and probably be good without further heroics and not lose much storage space.

HTH,
Bill

[Dennis Putnam]

Thanks. I thought about sistering but it was really the vertical supports under the top of the stairs that I was thinking about. I take it from your reply that I was in the wrong place. It is not support of the framing that is the concern (presumably that is good) but the flex of the stringers.

[Bill Graham]

Supporting the top of the stringers isn't too difficult, if the bottom is birdsmouthed onto a plate fastened down to the floor you have a compression fit. A birdsmouth at the top, couple of toenails into the face of the beam and a long screw through the stringer into the bottom of the beam(pre drill to avoid splitting the stringer) and you're good. Hangers work well if you just want to plumb cut the top, get a long one that'll get you from the bottom of the plumb cut and up onto the face of the beam and just make a small level kerf into the stringer at the point where the plumb cut meets the bottom edge.

Hope that's clear, kinda difficult to describe but easy to do. If you need a sketch let me know.

if you can, when selecting stringer stock get boards that are as flat sawn as possible. Most 2x12s come from the center of the tree, the vertical grain near the pith will split if you look at it hard and you'll have blocks splitting off if you put any sideways pressure on them.

Best,
Bill

P.S. LSLs or LVLs make great stringers, a bit pricey but a lot stronger than a 2x12.

[Joseph Tarantino]

+1 on the LVLs and also on the sistering. i've used double 2X12s for the stringers, leaving one un-notched (like a closed stringer) and sistering it to a notched (open) stringer. provides great rigidity.

[Richard Wolf]

Bill is right about the LVLs, excellent stringer material. Here are a few other things to do to beef up the stingers. Change the run, rise to 8" rise and 9" run. That will shorten your total run by almost 2 feet. Also the outside stringer which is free standing, why don't you sister a full 2x12 to the outside of it and make it a closed tread staircase.

[Dennis Putnam]

Thanks to all. I have one more question but it relates to a stair calculator I used.

http://www.blocklayer.com/stairs/stairseng.aspx

When it calculates the stringer cuts, it shows 2 versions and the point dimensions are different. Can someone explain what they are and which I should use? It appears to me I want the 2nd but I don't know what the 1st is supposed to be.

[Dave Zellers]

The difference is where you start measuring from, that's all.

[Bruce Wrenn]

For top support of stringers, drop down a piece of 3/4 plywood from header to level of bottom of stringer. You can double it on backside and use joist hangers cut into end of stringer to attach to plywood. Be sure and nail plywood well, as it's carrying the weight.