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Community and Q&A

Cedar Impressions over 2 inches of rigid foam?

Orrin Levine | Posted in Green Building Techniques on

Has anyone installed Cedar Impressions perfection shingles over 2″ of rigid foam? Certainteed says that you should only apply directly over 1″ of foam, but the client is looking for 2 inches and furring everything out would add significant cost and complexity to the project.

With the client’s consent, I’m considering applying the siding directly over the foam and using longer nails to ensure appropriate penetration into the studs. I realize the corners may take some thought to hit the studs, but can anyone think of something else that I am missing? Has anyone done this before?

Also any thoughts on using TYVEK drainwrap as a WRB instead of TYVEK homewrap between the sheathing and rigid foam would be greatly appreciated.

Thanks!

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Replies

  1. Sonny Chatum | | #1

    Orrin,

    I installed Cedar Impressions over 2 layers of 2" polyiso, but not directly. I used 1/2" ply over the foam, screwed on with Fastenmaster Hedlock screws, all the way to studs. My guess is that you could get away with what you propose, but I suspect any support from Certainteed will be absolute zero, if things go wrong. I have talked with them about such things.

    It's already a p.i.a. to install those shingles, even with a solid surface directly behind, because the interlocking tabs are really close in tolerance, often very hard to slip together, and you have to be sure you have actually locked tabs before you move on to the next shingle sheet. Uneveness in a foam surface might make that even tougher, in addition to possibly ending up with some visible waviness. The plywood over foam tended to make a pretty straight, coplanar surface.

    Another thing I almost forgot is that those things have to be nailed only at certain places, and you can't even have studs in all the right places. This is REALLY true for any pitched-roof gable ends, but also true for straight walls, I believe. If I remember correctly, the Cteed instructions call for installation over ply or osb, a solid plane.

  2. Orrin Levine | | #2

    Thanks Sonny. My thought was that if the foam was properly attached to the plywood sheathing, then it would be flat and have no waves. The concern is that the extra layer of 1/2 inch play on top of the foam would make the project cost prohibitive.

    Any thoughts on the drainwrap vs. traditional house wrap?

  3. User avatar
    James Morgan | | #3

    Orrin, if your client is asking for an off-book installation to save him/herself some money make sure you obtain from them a written waiver of liability so you're not on the hook when (not if) problems emerge.

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