Replies

1. 
   Peter Yost | Mar 11, 2019 11:30am | #1

   Hi Joe -

   As you have been studying resources on Airtight Drywall Approach (ADA), I am assuming that you have looked at the GBA video series on the topic: https://www.greenbuildingadvisor.com/article/green-basics/video-how-to-hang-airtight-drywall-1-of-3.

   Airtight drywall is only continuous within a space; intersecting interior partitions and floor assemblies break the approach and must be air sealed in connection with ADA.

   There is some debate on relying on sealant rather than gaskets for sustained air tightness with ADA. In my opinion, using sealant as a mastic where it is flattened by being pinned between the framing and the gypsum wallboard is quite different than applying a bead of liquid sealant that needs to maintain its adhesion to perpendicular or coplanar substrates over time.

   If I were doing ADA, I would be creating my air seal at margins and penetrations with gaskets rather than sealant, but the former are a lot more expensive than the latter.

   Peter

2. 
   joenorm | Mar 12, 2019 08:15pm | #2

   What is the most common way to create an air barrier for a house?

1. GBA Editor
   Martin Holladay | Mar 12, 2019 08:59pm | #3

   Norm,
   It's not one material -- it's a series of materials, with attention to sealing at the seams and intersections. For more information, see "Questions and Answers About Air Barriers."

2. 
   burninate | Mar 12, 2019 09:24pm | #4

   https://www.buildingscience.com/documents/digests/bsd-104-understanding-air-barriers

   Personally I favor some combination of an interior sheet good like Intello Plus (multiple sheets in the attic) AND dense-pack cellulose that's inherently good at blocking airflow AND taped plywood sheathing AND a housewrap. Redundancy. Air barriers become more important the more insulation you have, and the more air-permeable the insulation is - you don't want air to go into the insulation and deposit moisture on the far (cold) side or bad things happen. Evidently, small holes in air sealing are absolutely the norm, and this causes a very large fraction of moisture problems in walls and ceilings. The tendency of people to equate vapor barriers and air barriers has made the issue much worse - a generation was spent pushing taped interior plastic sheeting ('poly vapor barrier') as a solution to moisture infiltration of insulation, and that turns out to be exactly the opposite of what works.

   I agree with the theory that drywall should be a sacrificial layer, and that getting an ADA house that actually performs in both the short and long term is probably very difficult.

1. Expert Member
   MALCOLM TAYLOR | Mar 12, 2019 10:56pm | #5

   "a generation was spent pushing taped interior plastic sheeting ('poly vapour barrier') as a solution to moisture infiltration of insulation, and that turns out to be exactly the opposite of what works."

   I don't think it's at all that straightforward. In cold climates without air conditioning, poly works well. it is still the default method of both air and vapour sealing in Canada, and we simply haven't seen problems directly related to its use.

   I'm not advocating using poly - there are a lot of other better approaches - but it a bit revisionist to say that because we have developed other approaches, poly was a problem.