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Attic air sealing/gun foam failures?

Davin_ | Posted in Energy Efficiency and Durability on

After reading through Martin’s article on the cut and cobble technique… it seems that gun foam will usually fail over time and let air through.

https://www.greenbuildingadvisor.com/article/cut-and-cobble-insulation

In all the attic floor / air sealing articles I have seen, 90% of them are using gun foam.  Although he does mention if an entire top plate needs to be sealed a two part kit might be better.

Has anyone ever done a blower door with an attic that used gun foam and found after some years of expanding/contracting air loss increase?

Would it be better to avoid the gun foam all together and use drywall/wood caulked into place on larger gaps if not using a two part spray kit?

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Replies

  1. Expert Member
    Akos | | #1

    Foam failure is more to do with surface and application than type of foam. If applied over dusty surfaces, chances are it won't hold well.

    With the two part kits you do have to be careful with ambient temperature (can't be used in cold weather) and keeping your nozzles clean. Each start and stop means new nozzle.

    If you are not careful and the mix goes off, you can end up with a big mess that is very hard to clean up, I've been there a couple of times. Generally for air sealing larger surfaces like top plates and rim joist, the two part spray kits are much better and faster.

    When going with the one part foam, vacuuming the area before hand and misting it with a bit water helps a lot with adhesion. Once on clean surface, it will take a lot of building movement to damage the seal.

    For larger gaps, it is always better to plug the hole first. For example, walls with missing top plates, I cut 2x material to fill the gap than foam around the perimeter. When working in tight spaces, one part foam with gun is significantly easier an faster than caulk.

  2. CMObuilds | | #2

    I can give you actual data from my own house which was built in 2016. I’m a BPI certified building analyst and a general contractor so this isn't some box fan test. I saw your post and was in my home office so I grabbed the blower door and ran a test.

    My air sealing strategy on the homes I build revolves around 1 component foam out of a foam gun, with sealant in other areas where foam does not make sense. Little bit of 2 part kit foam in sills and other areas. I cant recall exactly, but I probably used around 2 cases of touch n seal all weather not including window and door around opening frames.

    The house has 4412 SF of conditioned floor area including the basement, 40213.4 cu ft of volume and 5316 SF of above ground surface area including the attached garage fire walls. That data is really close pulled from my Chief Architect plan files.

    So, using Tectite to run both tests and comparing both results side by side, my airflow increased from 366 cfm50 to 397 cfm50 an 8.4% increase. (Do not know margin of error here) that is .55 ACH50 to .59 ACH50; effective leakage area LBL ELA @ 4 Pa went from 20.1 in2 to 21.8 in2. Estimated costs of air leakage for heating went from $41 to $44, propane is actually the same price as I paid in March 2017 when I ran the first test I am referencing so no need to adjust cost data.

    Change obviously could be something other than the foams fault, we do have a few extra penetrations that were not in the envelope at the time of the first test.

    Anyways, thought it might interest you and Ive been meaning to get a fresh blower door test on the house anyways, so thanks for the nudge.

  3. Davin_ | | #3

    Awesome! Thanks for the replies guys!

    Akos - Makes perfect sense to make sure the area is clean, and misting with water to promote adhesion is something I have not seen anywhere else. This info should be added to more air sealing articles.

    T Carlson - What climate are you in? Good to see not much of a difference without knowing margin of error and other other penetration/s you mentioned. Will be interesting to see if anything changes with your house as the years go on...and glad my nudge was helpful for you

    1. CMObuilds | | #4

      Zone 6, around 8000 HDD.

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