self supporting wooden stairs with landing

[lubos1984]

Good Morning everyone,

I was called in to examine a stairway installed at a new build home. The stairway landing is supported by load bearing walls on two sides and by a hockey stick type stringer at the bottom. The base of the stairs rests on a double LVLs. I would think that the angled stringer would induce a moment at the edge that would need to be examined ?
Has anyone had experience working with stairs like this and is this sort of arrangement common ? I can see the architectural benefit of creating a large space below the landing on why they did this.
Thanks for all your help.

 

[1503-44]

The diagonal does not appear to be contributing to much of anything. Taking some of the landing load? I'd be tempted to remove it. If the stairs need that for support, I'd be very worried about the stairs.

 

[phamENG]

Interesting. I've seen plenty of prefab'ed stairs, but none quite like that. I'd be interested to see how they got that joint to work - and how long it will work.

Assuming they have a sound moment connection in that stringer, my concern is with the bearing at the base of the stringer. The bottom, diagonal edge of the stringer should land at the face of the support. In its current configuration, it encourages splitting of the stringer along the grain at the face of the support.

 

[KootK]

A model like this would have legs from a theoretical perspective.

 

[jayrod12]

I'm ok with what I'm seeing there. Would I prefer that the cranked landing stringer bear fully on the floor, yes, but is it likely to cause an issue long-term, I'd bet not.

I think that small 2x4 diagonal is just for erection and is likely removed already. The joint in that cranked stringer sure looks like someone spent a lot of time crafting it. Not sure what they've done for tensile continuity across the joint base but I feel with the almost moment connection to the stud wall, combined with the arching type action you'll get from that stringer, that I don't have major concerns.

 

[JoshPlumSE]

It looks like something the construction or carpenter used during construction..... Get the stairs stable and level before doing the final attachment to the bearing walls. Then just left it in place.

 

[phamENG]

KootK - good point. As long as the adjacent wall can take the thrust it would work. Though I imagine the floor will end up acting like a mini diaphragm that will "cantilever" off of the back wall.

 

[lubos1984]

thanks for your responses.
I don't think a proper moment connection is provided at the stringer / landing connection. (see pic below). it looks like a 2x4 is nailed as a diagonal support at the landing corner. KootK that representation is very helpful. Would a lateral reaction be required at the stud wall if the back of the landing is fully nailed to the ledger / stud wall. I would think that restrain would limit any spring action at the stud wall ?

 

[jayrod12]

That 2x4, as I indicated previously, was likely for erection. Koot's depiction of the restraint mechanism is what I was seeing in my head. That being said, that's a fairly long stringer for the upper stairs all sitting on this beam/stringer. Likely still ok, but something worth looking at nonetheless.

 

[Celt83]

The mansard framing from KootK's sketch could work, but from the picture the landing edge beam interrupts the post in the wall. the deeper facing material I would guess was really just intended to be a finish veneer but is probably serving to reinforce the mansard condition.

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[KootK]

Would a lateral reaction be required at the stud wall if the back of the landing is fully nailed to the ledger / stud wall.

Yes, it would be required in my opinion.

I would think that restrain would limit any spring action at the stud wall ?

It's not a deal breaker for the stud wall connection to be a spring. Rather, it's just something to be aware of, and possibly account for, in your evaluation. The more springiness that you have in that connection, the more bounce you might get in the stair (phamENG's point). If there's a real world issue to be concerned about here, assuming full height studs, I suspect that it will be drywall separation around the bottom of the stringer knuckle when that joint tends to open up a bit as the wall studs flex laterally.

 

[Skinnattittar]

There's actually quite a bit more structural support going on here than we typically give stairs with such awkward-to-assess details.

The landing/deck is pretty small, usually well assembled with nails/screws/hardware, and is going to be rigid once the plywood is attached. You can quite reasonably treat such a landing as a rigid beam and assess it as such;

This will give you some resultant shear connection loads to consider, and the added stringer will make it nice and stiff once you thoroughly secure it to the floor deck and platform corner to resist the lateral loads.

I wouldn't submit this as part of any kind of engineering thesis, though.

 

[IRstuff]

As strictly a homeowner, the brace doesn't look right, particularly after this last set of photos. It looks ad hoc, and it would seem to me that it should have been turned 90 degrees to increase the stiffness and properly mitered and nailed at that spot, if that was the intention.

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[KootK]

I'd bet a thumb that brace is merely a temporary erection aid.

That being said, that's a fairly long stringer for the upper stairs all sitting on this beam/stringer.

I'd definitely heed that admonition. The support of that long, upper stringer amps the stakes up a fair bit.

If you're using the full height studs as I proposed, and it's not been closed up yet, I'd take the opportunity to put a pair of studs on both sides of the stringer. KootK doth like symmetry.

 

[Jrit]

Based on the picture from below the landing, that oak piece appears to be veneered. It might be engineered lumber or something else.