Replies

1. GBA Editor
   Martin Holladay | Jan 22, 2015 04:06am | #1

   Ryan,
   In my opinion, the Airtight Drywall Approach is not obsolete -- especially for ceilings under unconditioned attics (the application that you are considering).

   Here are a few points:

   1. The advice you saw on the 475 web site was posted by a company that sells air barrier membranes from Europe, so it is clearly in the company's interest to convince readers that the products they sell are essential. Consider the source of the advice when you evaluate it.

   2. You don't need to install an expensive membrane to create an air barrier at a ceiling under a vented unconditioned attic. The logical location for the air barrier is at the drywall level; above the drywall goes thick cellulose. You are done.

   3. Making sure that your electrical boxes are airtight -- the most important feature of the Airtight Drywall Approach -- makes eminent sense in this location.

2. 
   Aaron Birkland | Jan 22, 2015 06:59am | #2

   Totally agree with Martin, ADA is not obsolete, particularly in retrofits.

   Was your builder or insulator familiar with ADA before you asked them? Do they have any experience with it? If not, that could explain their skepticism. Unfortunately, that could also explain their "significant" price premium - as it it would represent a risk to them if they are unfamiliar with the actual impact on labour & materials, as well as expected performance and customer satisfaction.

3. 
   Griffin728 | Jan 22, 2015 09:07am | #3

   Thank you both and I appreciate the tip on the electrical boxes. We will go ahead with the plan. You're correct that neither builder nor insulator (nor I) have used this approach. I know I am paying for their learning curve, but I kind of justify that and other energy related upcharges with the hope that they may use this again elsewhere in the future.

4. GBA Editor
   Martin Holladay | Jan 22, 2015 09:17am | #4

   Ryan,
   If you are interested in more information on the Airtight Drywall Approach, here is a link to an article on the topic: Airtight Drywall.

5. 
   user-1061844 | Jan 22, 2015 02:16pm | #5

   Ryan and Martin,
   would like to add the following. Yes, we at http://www.foursevenfive.com do indeed sell airbarrier materials (ProClima's INTELLO smart vapor retarder) that have been used in many Passive Houses and other high performance buildings that have been blowerdoor tested (and retested after a few years) to confirm to 0.6ACH50 limit.

   The points we bring up in out blogpost are true:
   1-ADA connections are not flexible (buildings move...),
   2-ADA is discontinuous (does not run from floor to floor or room to room)
   3-Drywall is a sacrificial layer (see image, but more prevalent are screw holes, etc)
   4-ADA does not address/reduce the number of penetrations made in the airbarrier by outlets etc
   5-ADA is not a smart vapor retarder

   Furthermore the IECC does list at interior gypsum as an airbarrier material in C402.4.1.2.1 but notes:
   "Materials in Items 1 through 15 shall be deemed to comply with this section provided joints are sealed and materials are installed as air barriers in accordance with the manufacturer’s instructions."

   GP and National Gypsum do not provide any instructions how to install interior gypsum as airbarrier or airtight (and for exterior recommend a WRB for airsealing), and although USG does mention acoustical sealant and air-tight connections - it does not provide actual instructions nor address points 1,2,3,4 and 5.

   
6. GBA Editor
   Martin Holladay | Jan 22, 2015 02:22pm | #6

   Floris,
   I stand by my advice.