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Icynene over exising drywall cathedral ceiling?

VE8mwTJ9fp | Posted in Energy Efficiency and Durability on

I had convinced myself to remove all the drywall from my cathedral ceiling, have closed cell spray foam applied to R15 against the roof sheathing, re-install the R35 fiberglass batts, and then have new drywall installed. I just read something interesting on the Icynene web site:

“Apply over a finished wall: If you don’t mind losing some space in your room, spray foam could be applied against new stud cavities on a finished wall or ceiling and a new finish applied on top of it. Note that a spray foam contractor will generally only install the insulation, so you would have to find another contractor to re-do the finishes and any other work required.”

Here’s the link:

I’ve done quite a bit of reading and have not come across this approach until now. Does anyone have any experience or advice on this method? How would this affect the amount of spray foam used? In my research, I found advice to use R15 against the roof sheathing to prevent condensation formation… Would this still be a concern?

I have a four level townhome in Alexandria VA that was built in 2005. The roof is vented. The entire fourth floor has a cathedral ceiling and it stays very warm during the summer–the ceiling drywall is quite warm to the touch during the summer days. There are numerous can lights and other penetrations through the ceiling now and I did my best to seal those up (there were gaping holes around many cans before I started). I’d look to limit the penetrations and eliminate the can lights. I’m pretty sure the cold weather performance is bad too. We didn’t get much snow last winter, but I did notice melt through in previous winters.

Anyway, I’d be interested to learn more about the approach of building out a new set of stud bays and applying spray foam against the existing drywall as explained on the Icynene web site.

Thanks all,

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  1. GBA Editor
    Martin Holladay | | #1

    Your original plan to open up the cathedral ceiling makes more sense than spraying Icynene on the interior side of your drywall ceiling.

    For one thing, you can't spray Icynene on the interior side of your drywall unless you first install new framing. In this case, you would need to install new ceiling joists under the drywall so that the Icynene installer would have framing bays to fill. Then the new drywall could be screwed to the new ceiling joists.

    More importantly, you have to think about where you air barrier is located, and whether your plan would achieve air barrier continuity. It's easy to imagine that you have lots of air currents in your existing insulation -- that's why the ceiling feels hot during the summer. Spraying Icynene on the interior side of the drywall would do nothing to address these air leaks. In effect, you would be abandoning your currently useless fiberglass batts on the windy side of your drywall, condemning them to a useless retirement.

  2. wjrobinson | | #2

    Change lights to any surface mount or eliminate.
    Add rigid foam foil face showing.
    Tape seams.
    Add 1x2 standard firring strips.
    Add finish material such as drywall or t&g wood.

    No mess, quick, less cost.

  3. VE8mwTJ9fp | | #3

    Thanks Martin. Thanks AJ Builder--do you mean that is better than spraying on the drywall or is better than/as good as removing the existing drywall and applying spray foam on the roof sheathing?

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