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HELP – Anyone experienced with old roof design how to insulate

kiwiscott | Posted in General Questions on

I have an older roof (1930) where there’s 2×6 rafters, the 1×2 strapping going horizontally across them. On top of this there’s boards and then asphalt. We are looking to insulate the attic.

I posted elsewhere that spray form might be the only choice — I need to use the attic so putting 13 inches of another product in the ceiling isn’t ideal. 

The question I have is: The strapping seems to create a continous airflow on the sides of the roof does this make it a problem to insulate – see image? Is there anything I should do before spray foaming.   It sounds awful but replacing the rafters in the roof to 2×10 is an option as I need a new roof (asphalt) anyway.


  1. freyr_design | | #1

    I don’t see a picture but aside from that question.

    Unless you are afraid your rafters are structurally unsound adding exterior insulation and new roof deck would be the more economical/easier/better option in my opinion.
    If you are reroofing anyways I would probably add a SA to your current roof deck to gain some air tightness, then build up polyiso, then new roof deck and roof on top. The one issue is that you will be adding weight, albeit not a huge amount to a potentially already undersized rafter system. I would talk with an engineer and getting approval/ suggested additions before this build up, especially getting a spec for fastening the new deck to existing rafters.

    I’m sure others will have other suggestions, the SA adds a little expense but it is a bit of insurance and easy air seal.

    You can obviously then add just batts to interior side to get a little more insulation.

  2. kiwiscott | | #2

    Hopefully this image works.

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