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Community and Q&A

Insulating solid brick house

Jdhogarth1 | Posted in GBA Pro Help on

Hello! I’ve been reading this forum for awhile now and there’s so much good information about insulating I don’t know which direction to head in. I have a 1950s ranch in Michigan that is under renovation. I currently have most of the walls exposed and wanted to know the best way to go about this. It’s a solid brick (like small cinderblock?) house with furring strips and 2 layers of drywall on the inside. On the outside I have furring strips with vinyl siding.

Would you recommend insulating the interior while I have it open, or should I wait till next year and do all the exterior in rigid foam when I replace the siding? Here is a picture for reference. Any tips to avoid a mistake would be greatly appreciated.

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  1. GBA Editor
    Martin Holladay | | #1

    Here is a link to an article that explains your options: Insulating Old Brick Buildings. Your house has one advantage over other old brick buildings: the vinyl siding keeps rain off the bricks.

    Two points:

    1. It's always better to insulate this type of building on the exterior rather than the interior.

    2. Because of the risk of thermal bridging, remember that you have to insulate all four walls for this retrofit work to be effective.

  2. Expert Member
    Dana Dorsett | | #2

    +1 on the exterior foam recommendation, since it would take less foam hit the same energy use performance numbers. If you're planning on re-siding, that's the right way to go.

    In zone 5 (roughly the southern half of the mitt) it would take R13 continuous insulation to hit IRC code-min performance with the insulation on the exterior, but R17 if on the interior. For zone 6 (the rest of the mitt, but not most of da-yoop) it would take R15 on the exterior vs. R20 on the interior.

    If you want to split the difference, 1-1.5" of interior side polyiso with 2-3" of exterior side EPS would work using the lower R-values, as long as the exterior R is not less than the interior, R, and they add up to R13 (zone 5) or R15 (zone 6) in total. An inch of polyiso is R6, and with 2" of EPS (R7.8 if Type-I, R8.4 if Type-II or Type-IX) on the exterior you'd be good for zone 5. With 1.5" of interior polyiso you'd have R9, and would be looking at 2.5-3" of EPS on the exterior.

    Due to cold-weather derating reasons you don't wan't to put polyiso on the exterior, since it performs poorly at the mid-winter extremes & averages. EPS gains performance a low temp, and is at least somewhat vapor permeable, which means the masonry can't hang onto enough moisture to rot out your window & door framing easily.

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