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I need recommendations for the best way to insulate and air seal the walls and floors in in house built in 1977 in the Seattle area.

Spbreslin | Posted in Green Building Techniques on

Existing walls – 2×4 @ 16″ o.c.
Sheathing – 1×8 boards
Siding – 1×8 lap siding to be removed
Existing subfloor – 2×6 T&G
Floor structure – 4×10 beams 4′ o.oc.
Min req’d R-value for the walls is R-21
Min req’d R-value for floors is R-30


  1. user-2310254 | | #1

    I think we need more information.

    Are you planning to replace the lap siding with new siding or something else? Have you considered adding at least some rigid foam to the exterior? Is your home over a basement or crawlspace? What about insulating the ceiling?

  2. GBA Editor
    Martin Holladay | | #2

    As we await more information from you, you may want to read this article to learn about wall insulation options: How to Design a Wall.

  3. Spbreslin | | #3

    The lap siding will be replaced but I don't want to go to the effort and expense of removing the sheathing if I can avoid it. I have considered adding a layer of rigid foam insulation to the exterior of the sheathing but I don't know if this will seal the leaky sheathing by itself. About 2/3 of the existing house is over a basement, the rest over a crawl space. The basement and crawl space communicate with each other and the basement is unconditioned. I'm not sure what you are referring to in your question about insulating the ceiling? Are you talking about the ceiling of the house or the ceiling of the basement. The current house ceiling is insulated but not to current code. The subfloor is also insulated and also not to code and it needs to be air sealed.

  4. GBA Editor
    Martin Holladay | | #4

    I notice that you have started two different Q&A threads on the same topic. That's confusing. Let's shut down this thread, please, and post all future comments to the other thread where several answers have already been posted.

    Here is the link to the thread we should be using: Best way to air seal and insulate floor and wall assemblies.

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