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Community and Q&A

Insulating a circa 1900 house (gut-rehab)

Duane Barron | Posted in Green Building Techniques on

I live in VA, zone 4A. I am trying to decide how to insulate a circa 1900 house with the interior completely gutted. It is a two story ballon-framed house with a brick foundation and a tall, steep roof. It has a standing seam metal roof in good condition. It has lap siding attached directly to the studs (i.e. no sheathing). I am considering foam and fiberglass bats for the walls (2 in of spray foam) and cellulose for the attic floor. I have also been reading this site’s posts about sealing up the crawl space and am planning to do this as well using foam board on the walls.

I am worried about spraying foam directly on the back of the siding. To avoid this I am considering installing 1 in. foam board and then an addition inch of spray foam.

Any thoughts about this plan? Any other suggestions for insulating the walls or other parts of the house?


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  1. GBA Editor
    Martin Holladay | | #1

    You're right: it would be a very bad idea to install spray foam directly against the back of the siding. Your suggested approach (installing a layer of rigid foam between the back of the siding and the spray foam) makes sense.

    If the time ever comes to replace the siding, it would be a good idea to install wall sheathing and a water-resistive barrier (for example, a layer of asphalt felt).

    Pay attention to air sealing at all phases of your rehab project. It's also important to upgrade any knob-and-tube wiring before insulation work begins.

  2. Duane Barron | | #2

    Thanks for the advice. I'm learning a lot on this website.

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