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Any potential problems with unexpected overkill?

Rich Singleton | Posted in Energy Efficiency and Durability on

I’m nearing completion on a new house build and I’ve asked the builder to take some measures above and beyond his usual process in the interest of comfort and energy efficiency (exterior rigid insulation, conditioned crawl, extra air sealing measures on exterior walls, etc…). I had also asked for air sealing in the attic around the penetrations and top plates. I’m not sure if there was a miscommunication but rather than focused air sealing they had the insulator spray a thin (1/2-1”) layer of closed cell spray foam over the entire roof deck!

This seems like it should do a good job of sealing everything, but it is not a strategy I have seen anyone use before. I’m a little nervous that there could be issues that I’m not aware of. For reference further attic insulation will be done with blown in cellulose to ~R-50, the attic is vented, house has an ERV, and there are some recessed cans but they are air-tight/insulation contact rated. House is in climate zone 4A.

Are there any potential problems with this approach? Seems like it might be expensive but I paid a flat price for the insulation/air sealing upgrades. Thanks in advance for any input you all have


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  1. GBA Editor
    Martin Holladay | | #1

    I understand that you have a vented unconditioned attic with cellulose on the attic floor. Air sealing efforts would normally be concentrated at the ceiling level (in other words, you want to make sure that the drywall under the cellulose is airtight).

    I'm confused by your statement that the contractor installed closed-cell spray foam "over the entire roof deck."


    1. Did you mean over the roof deck or under the roof deck?

    2. Is there any chance that the contractor may have installed spray foam above the ceiling drywall? Or was the spray foam really installed somewhere near the roof sheathing?

    If (as I suspect) you meant to write "under the roof deck," the spray foam is useless but not harmful. It's just a waste of spray foam. The biggest problem will occur in 25 years, when a roofer needs to replace a section of rotten roof sheathing. At that point, the roofer will curse your insulation contractor for stupidity.

  2. Rich Singleton | | #2

    Thanks for the reply,

    What I meant to say is the spray foam was applied to the ATTIC deck (floor of the attic or backside of the ceiling drywall. The underside of the roof is clear. The cellulose would be sprayed in on top of the CCF. I know it has helped at least some with air sealing given that all of the daylight that I used to be able to see coming up through the attic floor is now gone.

    Apologies for my erroneous wording,

  3. GBA Editor
    Martin Holladay | | #3

    The closed-cell spray foam was installed in a logical place. It will help with air sealing.

    That said, it never hurts to check the usual air leakage locations before installing the cellulose -- you want to verify that air leaks at penetrations, ducts, chases, and so on are well sealed before installing the cellulose. Remember that your attic access hatch needs weatherstripping and a tight latch.

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