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Questions about insulating 1947 concrete block home in Florida

flmach1| Posted inGeneral Questionson

We purchased a house in Orlando that we plan using as a rental. It is a one story block home, about 850 square feet. As with most houses built here during that time period it had no insulation with the exception of some blown in cellulose in the attic. We have gutted the house and found that originally there was no furring strips and drywall on the inside of the exterior walls, they have been painted and wall papered a couple of times then someone furred them out and put up wood paneling.

I would like to cover the entire inside of the wall with rigid foam and then put up strapping and drywall. My main question is could I have a mold problem with the old wall paper being between the foam board and the block wall? If that might cause mold problems what are some other options that will still improve the energy efficiency of the home?

Thanks

Nathan

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Replies

  1. GBA Editor
    Martin Holladay||#1

    Nathan,
    Q. "Could I have a mold problem with the old wallpaper being between the foam board and the block wall?"

    A. No. You can leave the wallpaper in place if you want.

  2. Dana1||#2

    FWIW: To meet code-min with continuous rigid foam in northern FL (zone 2A) only takes an inch of foil-faced polyiso. In southern FL (zone 1A) you could get there with an inch of EPS.

    If you leave the 1x furring between the CMU and use foil-faced foam, with another set of 1x furring between the foam and half-inch wallboard it would increase the performance of 1" foil-faced iso by about 50% or more. The dead-air spaces are also a capillary break, reducing the likelihood of trapping moisture anywhere in the assembly. Don't use foil or vinyl wallpaper (which could create a moisture trap with the foam), only latex paints.

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