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What is the best REMOTE wall assembly detail for airtightness?

David Perreault Nov. 10, 2022

Hello

I hope you are doing well.

I am preparing the construction of a detached garage where I will work in. I would like to build it with the REMOTE wall configuration.

My question is concerning the membrane to put outside the wall cavity. I want to use a peel and stick membrane so I can be very sure of the air tightness of the building ...but should I use an air barrier or a vapor barrier?

Thank you for your help and keep up the good work.

David

Responses (6)

Emmanuel Cosgrove
Emmanuel Cosgrove 2 weeks ago

Hi David

If it were me I would opt for plywood (see our article about why to use plywood sheating instead of OSB) and skip the membrane. If you put a high quality tape (Airstop, Siga, Cosella Dorken are a few examples) and not just the typical cheap red tape you get at building supply stores (as it is full of solvents and becomes brittle) then you will have an excellent air barrier and no membrane is needed there. And 8 inches of EPS foam as you know is a vapor barrier, so no need for 6-mil poly either. 

And I wouldn't say you even need the house wrap membrane on the exterior of the EPS, as long as you leave a vertical air space that is vented out the top then water will drain down and moisture will evaporate upwards and out. To that end, maybe check this page on how to install siding so walls can stay dry to make sure you have ample drying capability. 

 

 

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David Perreault 2 weeks ago

Hello Emmanuel

thank you for the reply.  This is very interesting and exciting!

I might go with the plywood and tape. But for the sake of my own comprehension, is the peel and stick membrane should  be air or vapor barrier? If the foam is already vapor resistant, I guess you can put the air barrier before or after it? The common order is vapor barrier and then air barrier but we could flip it right?

Thank you again and keep up the good work.

David

Emmanuel Cosgrove
Emmanuel Cosgrove 2 weeks ago

Well really the common order is air and vapor barrier at the same time, since most builders think of them as the same thing, which is almost always a 6mil poly barrier. But yes, air barriers can be anywhere in the wall system, and you can have multiple air barriers. Whether or not an air barrier membrane on the plywood was vapor-permeable or not would make no difference in your case since 6 inches of EPS is in itself, a perfect vapor barrier.  I keep giving you a new reading list, but for your comprehension you can check this one out - the difference between air barrier and vapor barriers. Glad you're finding value in the site, and we're always happy to help!

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David Perreault 2 weeks ago

This is great!!

Thank you again for the feedback and yes, your site is excellent and a great help for a lot of people.

All the best

David