Multiple air barriers – worth it or waste of money?
rbdbdr
| Posted in Green Building Techniques on
Hi, I’m building a house in Zone 4A. The walls itself are Faswall blocks with drywall up against the Faswall on the inside, and a quality self-adhered air and water barrier (Vaproshield RevealShield SA) on the outside of the block.
My question is whether it’s a waste of money to look into airtight drywall detailing in this case. The RevealShield detailing was expensive and looks to be very high quality — all details sealed correctly, everything solid, no visible holes or penetrations.
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These blocks are dry stacked, with the joints creating an opportunity for some air to flow from the interior, to the cold exterior air barrier and then back to the interior? Are the blocks moisture proof?
> no visible holes or penetrations.
Don't assume based on visible - do a blower door test.
Yes they are dry stacked on rebar and then concrete is poured in. The wall itself is highly porous and without any external barriers will definitely let air, water, and vapor through.
We will be doing a blower door test and were planning on doing the 'booger blaster' service (https://aeroseal.com/aerobarrier/) once the drywall is up on the wall, which (according to their FAQ) can seal the house down to .19 ACH50. I'll probably aim for <= .6...
Installing drywall to be air tight mostly just means running a bead of sealant in a few key locations as you hang the sheets of drywall. It’s really not very difficult to do, and adds little in the way of materials cost. I think it’s worth it almost always, especially on exterior walls and walls directly beneath attics.
Bill
Using the drywall as an air barrier has always seemed pretty silly to me. Every time someone hangs a picture you get a penetration in the air barrier. I also don't think I've ever been in a house that doesn't have cracks in the drywall in various places. Seems to me that using any finishing material, especially one as fragile as drywall, is just asking for future headaches.
Having worked with a couple of drywallers, I also wouldn't trust them with such a job in the first place.
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