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When designing a building that uses modern techniques like those featured in this Building Science article, such as exterior ridged foam insulation and a rain screen, how do you deal with the hideous looking overhang of materials extending way beyond the slab?

With 2" of foam insulation, 1/2" sheathing, 1/2" furring strips and 1/2" siding, there's a full 4" of wall covering on the face of the studs. So if the stud wall is built on the edge of the slab, you have 4" of overhanging materials, floating 6" above the ground. (Code requires a 6" minimum gap between the final grade and the bottom of wood members, so you can't fill the gap with dirt.)

I drew an example to scale to illustrate the problem. Essentially, the concrete wall comes up 6", then goes out 4" for the width of the materials, and then continues up. I think this is going to look ugly, especially near doors where there's a concrete patio slab outside instead of dirt.

I'm assuming that I'm doing this wrong, so could someone please tell me the proper way to design this type of wall so it's not unsightly? (And also functions as intended).

Should the slab be extended further, and the studs set back from the edge so the bulk of the rain screen, furring strips, and insulation sit over the slab?

siding Images

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I think the overhang is actually the better idea.

Imagine you are a water droplet running down the wall. With an overhang, you are more likely to fall harmlessly to the ground to be drained away. If you design the wall so that the slab and wall are even, that water is much more likely to wick under the wall and begin the long term destruction of the bottom of the wall.

The deeper the eaves on the roof and the wall overhang on the slab, the less likely you will be to have wall leaks and water damage.

If you want to seal the bottom of the wall you could install Z shaped flashing over the foam and under the siding.

Good luck!

  • This doesn't really address the aesthetics issue though. A lot of builders doing these types of walls are building higher end homes. I can't imagine many of those clients being impressed with a fat skirt 6" off the ground. I'm trying to figure out what is normally done... I'm sure some architect has come up with something clever? – Nick Sep 29 '17 at 13:41
  • Maybe you should go take a look at some of those higher end homes to see what they did. – ArchonOSX Sep 29 '17 at 22:31

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