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Community and Q&A

Retrofit insulation

dipolojarvi | Posted in GBA Pro Help on


I’ve got a 150yr old big house back house type farmhouse in Maine. Even though there was some blown in cellulous in the ballon frame construction, it’s cold in the winter (exterior walls feel very cold to the touch).

I’m debating between the following for adding to the interior side of exterior walls right up against the lath and plaster:

1. Putting up sheets of foam with drywall backing (how many inches is the best efficiency/cost choice)? Any caveats?

2. Putting up a two by four frame then filling with roxul insulation

Does anyone have some expert advice here? I’m concerned about moisture problems/condensation and air infiltration.

I have read other posts on this here, but no one seems to mention the roxsul option.

Thanks for your help,


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  1. GBA Editor
    Martin Holladay | | #1

    Adding insulation to your walls may help, but you might discover that what you really need is air-sealing work.

    A blower-door test will tell you how leaky your house is. The solution to a leaky house is called "blower-door-directed air sealing" -- you can enter those words into the GBA search box to learn more. Any experienced weatherization contractor or home performance contractor should be familiar with blower-door-directed air sealing.

    If you are confident that your home's air leaks have been adequately addressed, you can, of course, add R-value to your walls. You can install interior rigid foam if you want, or you can install almost any kind of new insulation between new studs or strapping. Most methods work just fine, so what really matters is that you choose a method that you are comfortable with.

    I'll finish with my usual advice: whatever approach you choose, pay attention to airtightness.

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