Michael Anshcell | May 03, 2018


details // Framing, WRB & Flashing, Insulation & Air Sealing

A Slick Transition from Foundation Insulation to Wall Sheathing

 

Outside insulation is an efficient way to keep heat in. The devil is in the details like this one

 

Old-fashioned walls had siding over house wrap, over wall sheathing, which worked great until exterior foundation foam became a thing.

R-15 foundation insulation is required in cold climates, like Minneapolis, and the best way to do it is to the outside. This means about 3 inches of insulation.

You could add a wide flashing to span the foam, but OA Design Build has another way to do it.

 

Step by step:

  • They begin with waterproofing on the outside of the foundation all the way to the capillary break on top.
  • Next comes the insulation.
  • Cantilevering the framing over the edge of the foundation about ½ in., leaves just enough space above for ZIP R-12 sheathing to flush out with the face of the foam.
  • The joint is then taped against air leaks.
  • The local building department requires a plastic slip sheet below grade, to protect against frost heave.
  • They also require a protective cover, like coil stock, above grade to protect the foundation insulation.

Now they can add a rain screen and siding for a neat transition that keeps the heat where it belongs.

 

—Michael Anschel owns Otogawa-Anschel Design+Build in Minneapolis, Minnesota

 

Detail and Download

Foundation to Zip Transition.jpg

Comments

No termite shield required ? Any concerns of insects burrowing up through the foundation insulation into the Zip insulation ? What holds the slip sheet and coil stock in place ?  Does the coil stock tend to 'oil-can ' ?

In the far north, we are still termite free, although that is really no excuse for not preparing for the inevitable influx of termites as the climate continues to change. So no, it isn't required, but yes, we should have thought about putting one in. 

Burrowing insects into insulation isn't something that we worry about much. It would be a long way to travel through the XPS and all the way up into the Poly Iso. I've not encountered anything like that. Without any moisture in the assembly, I'd question the value to the bug of making that trip. 

The slip sheet is held in place with a little magic and a lot of faith. It was the brain child of Dr Goldberg at the U of M and unfortunately made it into our codes. The idea is good, but she never developed or tested systems or materials before it became law. A number of us have challenged her on this issue, but we're stuck with it for another 4 years. The purpose of the slip sheet is to keep soils from freezing and bonding to the below grade insulation, and then potential ripping it out of the ground when it heaves. (Again, this is Minnesota where the ground freezes down to over 3' in the city and at almost 5' an hour north of that.) A hydrostatic pressure release mat would work just as well, in my opinion, but for now we wrap a piace of 6 mil poly up the side of the insulation and fasten it to the framing. It gets ripped free during back fill every time. This is a long way of answering your question on what hold the slip sheet in place. At first, staples and cap nails, and after that the weight of the earth.

Coil Stock - the coil stock is protection board for the XPS that is exposed above grade. Slab on grade is very unusual here. Most homes are 12-24" above grade here, so you have that much exposed XPS. We glue coil stock onto the XPS as part of the cladding installation. I haven't had much of an issue with it oil-canning, although that was a worry initially. being bonded to the insulation seems to help quite a bit. 

now how do I attach manufactured stone to the outside of the rigid foam insulation per customer request? Show me a detail and video on that!  Great video by the way. 

I couldn’t agree more!  I want to see this detail but with manufactured stone on the foundation.  Give me that detail, but you never see it. 

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