Gable Wall with Stairway 3

[medeek]

I've come across this a number of times with my own designs and now this particular design:

A stairway next to a gable wall or exterior wall. My first thought is to call out a balloon framed wall up to the 2nd story top plate(s) but then that makes the rim board and double top plate of the first story discontinuous. Any thoughts on the best way to frame this small section of wall next to the stairs?

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[mike20793]

Can you use the rim board to span across the opening caused by the stairs? It may be okay as discontinuous since you have LVLs that can be detailed to brace the wall at the termination of the rim board and double top plate.

 

[BSVBD]

Treat the wall for what it is - a tall wall.

Either double the studs [(2)2x6 at 16" oc], use 2x8's at 16" oc, use LVL or Paralam studs if necessary, which i doubt this wall is tall enough to warrant such.

All will depend on your lateral calcs.

 

[medeek]

Here is a quick mock up in SketchUp to better explain what the two options are:

You can also view and download the 3D SketchUp model here:

https://3dwarehouse.sketchup.com/model.html?id=uf979b67e-2755-4981-9bfc-06d20b64d313

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[jdgengineer]

Is the sketchup model missing the low rood rafters? They should also be able to brace the wall but you would have a hinge if they are not located at same height as rim. I would either balloon frame the wall or design the rim to clear span in weak axis bending across the stair opening. I most commonly balloon frame. If you balloon frame I would block and strap at the rim elevation for continuity.

 

[medeek]

The actual building will have a hip roof but with trusses, disregard the roof. Yes it is missing the ceiling joists, collar ties etc...

The balloon framing makes more sense to me but then I realized I was losing a lot of continuity in the rim joist, first floor top plates and second floor bottom plate. I've run into this before and have never answered fully in my mind which is the better solution, and why.

I like the blocking and strapping at the rim joist, that would solve the continuity issues.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[DETstru]

From a construction standpoint, I would think maintaining uniformity (no balloon framing) would make things simpler. Though I'm not sure it's really enough of a concern to be problematic.

 

[medeek]

Agreed, from the contractor's view platform framing this particular location would make more sense.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[jayrod12]

What about LVL top plates on that wall, No splices allowed at the opening, is there capacity as a wind beam then?

I would do everything I could to make it work as platform framed, only because then I would be confident it will get built right.

 

[medeek]

The opening is 10'-10" (130") or 13 stair treads at 10". The span is not exceedingly large. If no splices are allowed in the rim joist and the second floor bottom plate and first floor top plates as well as an LVL positioned on the interior then one could easily consider this a box beam of sorts with the flanges of the beam formed by the interior LVL and the rim joist and the webs formed by the plates. Even without running any numbers I'm going to venture a guess that this should be pretty closing to passing. The tributary length is approximately 9', the ASD wind pressure is about `23 psf, so we have about 207 plf on this beam from the wind perpendicular to the wall.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[mike20793]

You could always double up the rim board at the stairs and maybe use and engineered lumber rim board. I use it all the time to support brick, rim board as headers over tall windows, etc.

 

[KootK]

I usually do it Mike's way because I get a lot of flack for balloon framing. I include the lateral effect associated with an assumed 2" out of plumbness at the rim to account for instability. Because the rim board is wall bracing, I would really like to be evaluating rim lateral stiffness as well. I haven't gotten around to making a speadsheet for it however so, thus far, it's gone unchecked.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Teguci]

Any thoughts to strapping some of the wall studs over the rim joist?

 

[jayrod12]

We've had this discussion a few times about the strapping the studs. I believe the consensus was that by the time you account for shrinkage and nail slip, the strap doesn't really end up providing any significant improvement.

 

[KootK]

Yeah, the last strap-chat was me: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[medeek]

If I'm going to go the platform framed method I also really like adding an additional rim board or LVL (as I have drawn in the very top picture above) that is spaced so that it is flush with the interior wall. This eliminates the eccentricity described by KootK and also provides a cavity for insulation and electrical. Provided that no splices are allowed in these members as described above I think this is the optimal solution and less likely to be messed up by the contractors. As others have mentioned balloon framing seems to cause problems for builders.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[Teguci]

Wouldn't these problems also occur with the strapped and blocked balloon framing?

 

[jwilki]

Definitely provide a wind beam over the stair well. Aesthetically I think the balloon frame wall is a lot less rigid, if constructed the occupant can feel the difference between his stair well framing and the nominal wall framing. Not to mention, you have more relative movement between the balloon frame and standard frame either side of the stair well which can crack brittle finishes.

 

[medeek]

The stairs coupled with the interior wall on the other side of the stairs all connected to the floor exterior wall will also server to stiffen up this exterior wall to some extent. I think we are probably overlooking some of that redundancy within the structure.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[KootK]

If I'm going to go the platform framed method I also really like adding an additional rim board or LVL (as I have drawn in the very top picture above) that is spaced so that it is flush with the interior wall. This eliminates the eccentricity described by KootK and also provides a cavity for insulation and electrical.

1) I like the double rim board as a composite member if possible. It's stiffer that way. If you're going to separate the plies, you'll either need to treat them as two individual bending members (more deflection) or find some way to stitch them back together intermittently.

2) This method doesn't eliminate the eccentricity I had in mind. The sketch below shows what I was getting at originally. It was overly optimistic not to include it in the first place.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.