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Okay to use Open Cell foam over existing batt insulation or foam board? I’m located in Zone 5a.

fj5GwJKDnK | Posted in General Questions on

I have a bonus room that has accessible 3 walls and the ceiling. The room is already insulated on the walls with R-11 and R-3 foam board. I have had two contractors now tell me that they can spray over the existing insulation with open cell foam vs. removing it. I’m curious as to why it wouldn’t be better just to remove all the existing insulation [wall and ceiling], spray foam the back of the drywall between the studs; and then put back up the R-3 foam board on the walls and batt insulation up on the ceiling? I would think it is technically a better air seal by applying directly to the drywall and any cavities present vs. spraying on top of existing insulation?

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  1. wjrobinson | | #1

    Did you ask your bidders this question? Someone who does this job for you has to do what he has success doing. Sprayfoam that cures correctly is hard to screw up. Others may understand what you are proposing, I can only half see it. Next.....

  2. fj5GwJKDnK | | #2

    I did ask the contractors and they both are the ones who suggested to spray directly over the insulation.

    But everytime I see this done on TV; existing insulation is removed and re-applied on top of the foam.

    FYI, this bonus room is in the 2nd level of the house and is surrounded by open attic space. It is finished but I have ability to access the exterior of the room via the attic and remove the foam board and spray directly on the batt insulation. Or, I was thinking; removing all the insulation [batt and board] and spraying directly onto the drywall. I would then have the ability to lay down the batt insulation over the top of the sprayed on foam insulation if I chose too and even put back up the foam board too

  3. GBA Editor
    Martin Holladay | | #3

    You didn't tell us whether the R-3 rigid foam is on the interior of the stud walls or the exterior.

    Are the contractors suggesting that spray foam be installed against the rigid foam board or against the fiberglass batts?

  4. wjrobinson | | #4

    Martin, the ridged foam is on the cold attic side.

    Don, your idea is wrong because your situation is different than your tv show.

    Do it the way the sprayfoam contractor wants to do it. Use the most experienced one. Ask the crew when they did their first job and go see one of their in progress jobs.

    Good luck.

  5. fj5GwJKDnK | | #5

    AJ Builder,

    Correct, faced batt insulation is against the drywall with the face against the warm side [bonus room] with the ridged foam attached to studs on the cold side over the batt insulation. So, contractors both told me to simply add open cell spray foam over existing insulation since a vapor barrier is already in place and not hurting anything.

  6. wjrobinson | | #6

    Don, exactly. Ready set go. Spray away.

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