Option for Correcting a Stem wall Mistake
idahobuild
| Posted in General Questions on
Hey all,
The concrete sub messed up the front stem wall by making it 8 inches thick instead of 6 inches. My bottom plate hangs over the stem wall by 1.5 inches to cover the under slab insulation and we have 2 inches of exterior insulation planned. That leaves me with about 2 inches of exposed concrete extending just below the siding.
I am looking for proposed solutions to this mistake. Please let me know what you folks think.
Thx.
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Any thoughts on this...?
Make a thicker wall?
How about like a concrete metal cap then to metal coil stock? (picture like like z bar flashing just extremely wide)
"My bottom plate hangs over the stem wall by 1.5 inches to cover the under slab insulation "
I'm having trouble interpreting what this means. I assume you have a slab? Normally a slab would either be flush with the top of the stem wall, or the stem wall sticks up a bit above the slab.
Can you draw a picture of what you're trying to do?
6" sounds really narrow for a foundation wall BTW.
Hey DC, drawing attached. Looks like I actually still have a slight overhang of siding on stem wall.
As to the stem wall thickness, I suppose I just have to trust the structural engineer that stamped the drawings.
Idahobuild,
A couple of small things.
- Unless your siding extends past the foundation below, you need to hold it up to provide an air-gap and drainage path at the bottom of the rain-screen. That will expose the Prosoco, so you would be better off using metal flashing. You also then need to figure out how to protect the bottom of the rain-screen cavity and the foam, which is now exposed.
- Thin your interior foam to end up flush with the outside of the sill-plate, so you still have some R-value at the top of the stem-wall.
Thx Malcolm.
How far should I hold the siding? AND, to confirm, I would I hold up the battens and XPS as well?
Does it make much of a difference that this particular wall is under the front porch...about 7 feet?
Idahobuild,
You can leave the insulation down on the stem-wall, and if the foam is detailed as your WRB, the flashing can taped to the outside of your foam. Lift the siding 1", and cover the bottom of the battens with perforated flashing or Cor-a-Vent
idahobuilds,
Use Z flashing with a drip-edge to cover the exposed top of the concrete. Make sure to air-seal the base of the framing first.
Not long ago I had a contractor misread my drawings and they formed the concrete to what should have been the outside of 6" exterior foundation insulation. We just made the house larger; is that an option for you?
Hey Machael, in our case, since the bottom plate is cantilever to the inside, it actually makes the house smaller by 2". I suppose that if we put the bottom plate on a 1/2 " cantilever we could get 1 inch back. But with that scenario, I worry a bit about what the finished floor (concrete) would look like.
Got it. It would be a lot of work but if you don't want the foundation to project beyond the siding, you could cut a 2" shelf into the interior. That's how I detail slabs with stem walls anyway. If your drawings, specs and/or contract were clear, the contractor should pay for the change, or at least share the cost.
From your drawing, the slab insulation is correctly tapered at the top of the stem wall so that the slab can be poured over it. I don't see the need to overhang the bottom plate here.
Hey Salty - the insulation is tapered at the top. However, the top edge doesn't perfectly rest on the top edge of the slab (the insulation is a bit "wavy"). So, it make a bit of an imperfect finish since our finished floor will be the polished concrete.
I hope that makes since.
SaltyDog701,
You have to be careful. Our code specifies the R-value of slab edge insulation, and tapering the top makes it non-conforming.
Or is this a partial wall with the slab lower?
So if I'm getting this right, the issue is that instead of overhanging the stem wall 1-1/2" the bottom plate is set back 1/2" from the edge of the stem wall by 1/2"? And the slab is going to be poured to be even with the top of the stem wall?
I don't see what the issue is. The interior wall will typically have 1/2" drywall, plus baseboard and shoe molding, each 3/4". So even if the concrete slab isn't perfect where it joins the stem wall, you've got 1-1/2" from the edge of the stem wall until you have any visible floor.
What is the order of construction? I'd have them pour the slab and screed it flush with the top of the stem wall, then put in the top plates where you want them.
DC,
I understood the problem to be on the exterior, where the concern was the stem-wall extended out past the cladding.
I guess it depends on where you put the extra 2". I say put it on the inside, I don't like the idea of that lip.
DC,
There is something to that. Although unless the wall can be moved far enough that the sheathing is flush with the concrete below, you still need some flashing to direct water out of the rain-screen gap.
I've pretty much given up on adding interior shelves to stem-walls. I cant the top at the exterior at 45 degrees, leaving whatever flat bearing area is needed. That makes the engineers happy, and gives you a bit of wiggle room if your walls aren't exactly co-planar.
Since it is one wall, you can also bump up the exterior rigid to get it flush with the concrete. 4" rigid is not that much fun to attach but it is only one wall.
Another option is simply using thicker furring strips for the siding.
You can also bump up the wall studs to 2x8.
Hey all,
I met with the GC today and we discussed a few options (some from this thread). The GC is suggesting a relief cut to the inside so that we get the bottom plate back where it is on the plans.
See atch'd
idahobuild,
If they are willing to do that, it is by far the best option.
So I feel like I'm really dense here. I just don't see what moving that concrete joint two inches to the right in the picture buys you. In either case the joint itself is going to be concealed.
DC,
As I understand it, the original stem-wall was supposed to be 6" wide at the top so that the sill-plate could overhang at the interior to allow a layer of foam between it and the slab. Because it was poured at 8" this wasn't possible, and the discussion has been around how you deal with that to maintain an open rain-screen gap at the outside, while still having space for the interior slab edge foam.
I don't think the sketches reflect how the finished relationship will be. If the slab is returned to a 6" thickness at the top, there can be 2" of foam with no taper next to the slab. Something like this - although I forgot the sheathing, and there is probably sub-slab foam:
If they built it the way you have it drawn then that makes sense, the top of the foam has to be concealed because the concrete is the finished floor. But all of the drawings show a beveled edge to the top of the foam, so that the point that needs to be concealed is just the inner edge of the foam, which is covered by the wall.
I guess there's some concern if the finished concrete is too thin it could crack in time. In that case, I'd question whether even 1-1/2" is thick enough, so it doesn't matter whether it's the thin part or the thick part which is exposed. Which rules out the beveled foam altogether.
DC,
The beveled foam detail is one that appears on GBA a lot, but since our recent code amendments requiring certain levels of slab edge insulation, I've been getting push-back from our building department, saying that the required thickness needs to be continuous. Here anyway, it's seen as non-conforming.
The depth of the cut appears to be 6", leaving the slab thickness unchanged at 4"
Malcolm --
The beveled foam detail has been in every drawing that the original poster, idahobuild, has posted. If I wasn't clear in my previous posting, yes, if you don't do the beveled foam then you have to figure a way to cover the exposed foam. But idahobuild has never indicated that he had a problem with the beveled foam.
I guess it's academic at this point if the contractor has agreed to cut the shelf.