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Gable Wall with Stairway
3

Gable Wall with Stairway

Gable Wall with Stairway

(OP)
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
www.medeek.com

RE: Gable Wall with Stairway

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.

RE: Gable Wall with Stairway

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.

RE: Gable Wall with Stairway

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.

RE: Gable Wall with Stairway

(OP)
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
www.medeek.com

RE: Gable Wall with Stairway

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.

RE: Gable Wall with Stairway

(OP)
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
www.medeek.com

RE: Gable Wall with Stairway

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.

RE: Gable Wall with Stairway

(OP)
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
www.medeek.com

RE: Gable Wall with Stairway

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.

RE: Gable Wall with Stairway

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.

RE: Gable Wall with Stairway

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

RE: Gable Wall with Stairway

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.

RE: Gable Wall with Stairway

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.

RE: Gable Wall with Stairway

(OP)
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
www.medeek.com

RE: Gable Wall with Stairway

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

RE: Gable Wall with Stairway

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.

RE: Gable Wall with Stairway

(OP)
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
www.medeek.com

RE: Gable Wall with Stairway

Quote (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.

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.

RE: Gable Wall with Stairway

(OP)
If the plies are separated doesn't that give the whole assembly more section modulus? Solid blocking between the plies 24" or 32" o/c should help to further stiffen things up. I will post a detail shortly.

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

RE: Gable Wall with Stairway

Two separate, independent plies would be twice as stiff as a single ply. However, two plies snug and composite would be eight times as stiff as a single ply. Two plies separated by a gap but made to act compositely would be better still. The trick is making the separated plies behave compositely. Blocking would be one way. Another would be using the plates above and below to stitch the plies together into a box beam. You'd probably be stuck with toe nailing on the bottom though. Nobody loves toe nailing.

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.

RE: Gable Wall with Stairway

Upon further inspection, I see that you've already thought of the plates as the webs of the box beam.

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.

RE: Gable Wall with Stairway

(OP)
Not much really going on here, but here is the detail:

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

RE: Gable Wall with Stairway

(OP)
A solid bead or two of LN/LNP-902 (Liquid Nails Subfloor) probably wouldn't be a bad idea either to make sure the LVL-plate-RIM assembly works as a unit.

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

RE: Gable Wall with Stairway

(OP)
WFCM Fig 2.1k Floor Diaphragm Opening Limits:
Exterior walls adjacent to the opening shall be framed using full height studs where the opening is less than 2' from the exterior wall.

Then if you turn to the prescriptive section is shows a stairway next to a platform framed wall...

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

RE: Gable Wall with Stairway

(OP)
The big question is can we make the boxed beam work as a single unit, does that assumption hold true? Or is the safe bet a "wind beam" at this location?

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

RE: Gable Wall with Stairway

I vote yes, we can make it act as a unit with some attention to detail. Not sure what the difference is between this and a wind beam though.

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.

RE: Gable Wall with Stairway

(OP)
When I hear "wind beam" I assume you replace the void and LVL with a larger glulam or PSL beam. Disregard any composite action with the plates and just run the numbers on the beam taking the full out-of-plane load. This would be the safe bet, especially if the length of the opening gets larger. The 12'/50% rule in the WFCM should place a limit of 12' on the max. length this "wind beam" should have to span.

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

RE: Gable Wall with Stairway

Why is the opening in the second floor same as the projected length of the stairway? Why not minimize the length to that required for headroom?

RE: Gable Wall with Stairway

(OP)
Good question AELLC2.

The ceiling height in the model is shown as 8'. In reality it will be 8'-1". Subtract about 7.5" for the first step gives me a headroom of about 89" give or take an inch or two. This is assuming there are 13 treads. The framer may opt for 14 treads instead which would give me about 81" of headroom. I always like to err on the side of a little extra headroom for a stairway, for reasons of meeting code and also for functionality for the occupant.

In this particular instance the client made a point that they wanted more headroom and width so moving large pieces of furniture into the upper floor space would be less problematic. I've damaged a lot of drywall in my lifetime moving stuff up and down tight stairways.

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

RE: Gable Wall with Stairway

I think there is great conversation going on here and I don't mean for this to come off badly, but do you think this conversation is tredding into "penny wise, pound foolish" territory?

In my area I wouldnt get much grief for balloon framing 15' of area. Deflection I don't think is a concern as you have an adjacent low roof that can brace the wall.

I think where I would run into flack would be when I tell the contractor they have to use:

1) Continuous rim with interior LVL beam.
2) put beads of liquid nails to help bind them together.
3) nail them together with nonconventional nailing.
4) but small strips of blocking between the two.
5) insulate the space prior to closing (likely out of sequence)

If it were me and we werent using balloon framing, I'd 100% go with full width 4x10, 6x10 or PSL rim to span in weak axis across the opening. Sure the material may be more expensive but less labor and less likelihood of missinstallation.

RE: Gable Wall with Stairway

(OP)
The porch roof will help brace the wall, I wasn't going to consider that but it probably adds a significant amount of stiffness to the entire assembly when you consider an 8' deep diaphragm.

I agree that the safe bet is just to put a "solid" beam into the slot behind the rim joist and eliminate most of the special detailing required to form a composite beam.

Regardless of using a "wind beam" there still needs to be appropriate connections between the wall plates and the beam so that the loads are properly transferred into the beam from the the wall. What would be a more conventional way to nail the plates to the beam? I still think you are toe nailing into the first floor top plate and nailing down through the second floor plate as shown in the detail above, I'm not sure how else to do this.

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

RE: Gable Wall with Stairway

(OP)
A few options:

1.) 1-1/4" Rim Joist on exterior with a 3-1/2" x 9-1/2" PSL beam behind to span the 10'-10" of the stairwell.
2.) Remove the Rim Joist in this section and install a 5-1/4" x 9-1/2" PSL beam that spans the full 10'-10" of the stairwell.
3.) Remove the standard Rim Joist (1-1/4") along the entire length of the wall (24') and install either a 3-1/2" or 5-1/4" continuous PSL beam the entire length of the wall.

Or perhaps some other option I've overlooked.

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

RE: Gable Wall with Stairway

(OP)
With option 2, you would probably want to install straps between ends of PSL and Rim Joists.

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

RE: Gable Wall with Stairway

(OP)
The porch roof actually is pretty close to the rim joist, see image below:

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

RE: Gable Wall with Stairway

I agree that the porch diaphragm gives you something but I'd be pretty hesitant to rely on it.

1) Normally, I'd assume the porch to be loading the wall laterally, not bracing it.

2) To utilize the diaphragm, by the book, you'd probably need to connect a bunch of things that aren't, by default, typically connected.

3) Owners generally feel at liberty to modify things like porches as they see fit. Most lay people -- and builders for that matter -- are unlikely to recognize the role played by the porch diaphragm in stabilizing the wall joint. And you're unlikely to saddle the building with some kind of plaque to that effect (porch removal = death).

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.

RE: Gable Wall with Stairway

(OP)
I probably should have checked the numbers first. Given the high wind loads in our area (155 mph ult.) a 3-1/2 x 9-1/2 PSL loaded in the weak axis will deflect almost a full inch with a clear span of 10'-10" and a trib. length of 9'. However, a 5-1/4" beam will pass with flying colors, so I've updated my detail to:



The eccentricity is small enough that I think it makes sense to just sandwich them together and make sure they act as one unit. I still like the idea of disallowing any splices in the members in this region of the wall and will keep my notes specifying that.

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

RE: Gable Wall with Stairway

I like your new detail a lot better.

I'd personally let them splice the wall plywood at the rim but up to you. It's where they want to splice it and anywhere else would require blocking (assuming you have blocked shearwall).

RE: Gable Wall with Stairway

(OP)
The second detail should be pretty stout. The top and bottom plates will also contribute as well as the sheathing when the wall is sucked outward.

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

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