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New build: thoughts on Exterior rigid foam applied on top of Advantech zip sheething and Tyvec drain screen?

green654 | Posted in Energy Efficiency and Durability on

We are partway through framing of our new house and I’ve been learning a ton about the importance of external continuous foam insulation
boards. The problem
is that my builder is half way through the framing and we’ve used Advantech zip sheething with Tyvec Drain Screen. Can I add a rock wool foam insulation board to the outside of the drain screen in between the drain screen and Hardie cladding? Also, do I need a rain screen air gap with furrings if I stick with Advantech zip plus Tyvec drain screen?

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  1. kbentley57 | | #1

    Hi Green,

    I'd replied to your previous question about the Tyvec / Hardie board and rainscreens. This one is slightly different, but I think you have a bit of terminology mixed around.

    1. I wouldn't say you have a problem. If your builder used Zip sheathing, you're already a leg up on most residential construction. Adding Tyvek on top of that only enhances it in my opinion.

    2. Exterior insulation can be added applied to the outside of essentially any Tyvek building wrap, and Dupont has many installation documents detailing this. To help us, and yourself out a little here, can you tell us exactly which product is being used?

    here's a link to get you started:

    3. Rock wool is not a foam, it's more similar to fiberglas in that it is made of spun fibers, and is not plastic. It can be applied to the exterior of the Tyvek as well, but a better solution (depending on where you're located, edit your question to put that in if you can) is probably XPS for the ease of installation, cost, and R value.

    4. Most of the houses ever built in the US have been built without a rainscreen. Think of it as an optimization of the wall assembly. It's better to have one, than not to have one, but I wouldn't say it's impossible to build a good home without it. If you're willing to spend the extra money to have your builder install it, it will only make your home better.

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