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Community and Q&A

How to add insulation

user-1084973 | Posted in General Questions on

We built a log/timber (Lindal Justus) home in 2000 and insulated our 12″ roof rafters (I beam) with 6″+- of icynene per thier recommendation. We are now realizing that even though we passed all our inspections and no signs of ice damming this is not enough insulation. The footprint of the home is 1000 sq ft and our rooflines are simple. We have a 12/12 over about half and a 4/12 on the rest. The ceilings are all cathedral with 12″ I beam with metal cross braces about half way and finished with 1/2″ plywood and shingles on top and 1/2″ drywall in the living area. Suggestions on getting more insulation into these bays without removing all the drywall or running into moisture issues? On a side note, we also do not have a moisture barrier.

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  1. tamfflcommissioner | | #1

    Nope. Take the shingles off. Add on 2 layers of 2 inch rigid foam. Make sure you offset the joints horizontally and vertically. Then add another layer of plywood. cover the roof with peel and stick membrane. Then furring strips run vertically. Then another layer of plywood. Then tar paper and shingles. Be relly careful about flashing any penetrations and understand what you are flashing to. Oh, and hire an engineer to make sure we aren't mis-guiding you.

  2. homedesign | | #2

    Jeff: "Then furring strips run vertically. Then another layer of plywood. Then tar paper and shingles."
    hey Jeff ...I don't know if the peel and stick layer is such a good idea?
    but that "over-roof" sounds like a good idea...(similar to many European examples)

    Are you the same Jeff Melvin who works for Joe?

  3. user-869687 | | #3


    You can blow cellulose into the empty 6" space below the Icynene, for about R-44 total. That's above code minimum (most places). This will require at least one hole in the ceiling for every rafter bay. It might be easier to add a layer of 1/4" drywall when the insulation is completed, rather than attempting to make all those holes disappear. You need to find someone who knows how to dense-pack cellulose to 3.5 pounds per cubic foot, for optimal thermal performance. There's no reason this would cause moisture problems.

  4. tamfflcommissioner | | #4

    Worked for.
    Are you the same John Brooks I met the first time I saw Joe deliver Building Science Fundamentals?

  5. homedesign | | #5

    Hi Jeff,
    I talked with you briefly at Summercamp (or another Jeff Melvin)

    I took "Fundamentals" twice
    Once in Houston and a couple of years later in Dallas
    I will take it again if Joe & John come back to Dallas.

    here's a sample of "Fundamentals"
    here's another video I recently stumbled upon

    Edit to add...
    here is a Link to the "Seminar" Site
    there is lots of stuff that you will not see at the usual BSC website
    powerpoint presentations etc

  6. tamfflcommissioner | | #6

    Yes, but I met you in Houston...:)

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