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Can I blow in insulation above Homasote ?

Rob73 | Posted in Energy Efficiency and Durability on

I have a cabin that has a 1/2 inch layer of Homasote as the ceiling in the main living area. We just added heat and air conditioning and I wanted to blow in Insulation (cellulose) in the 5 1/2 inches above the homasote. Will this cause excessive moisture to accumulate and will the Homasote bulge from the extra weight and humidity. I found a product at Lowes that is 3 1/2 fiberglass insulation covered in plastic on both sides that I might be able to get down there. Would this be a better idea? The cabin has a metal roof with no eave vents or ridge vents. Thanks

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  1. GBA Editor
    Martin Holladay | | #1

    Rob,
    It sounds like you are describing a sloping roof assembly rather than an attic floor. Am I guessing correctly?

    There are a couple of problems with your plan, and the stiffness of the Homosote is just one of them. If you want to use cellulose to insulate a sloping roof assembly, you must have a ventilation channel between the top of your insulation and your roof sheathing (or roofing). You also need an air barrier on the interior side of your insulation, and I'm guessing that your Homosote isn't airtight.

    Your best bet is probably to try to install a couple of layers of rigid foam on the interior side of the Homosote, followed by 1x4 strapping and drywall.

    For more information, see How to Build an Insulated Cathedral Ceiling.

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