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Community and Q&A

Flat roof insulation

WsrCqDZ5ni | Posted in Energy Efficiency and Durability on

We own a 100-year-old brick house with a flat (very low slope) roof. The attic space above the second floor goes from about 18 inches at the front of the house to 6 inches at the rear. The roof itself is about 10 years old and in good shape. Despite it being white-coated last year, we still feel a significant heat difference upstairs in the summer.

We are considering putting blown-in insulation in the attic, but worry that without maneuvering room in the attic to verify good coverage we might just be wasting the money.

Any advice on how to improve insulation without completely tearing off the ceilings and/or roof would be greatly appreciated.


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  1. jklingel | | #1

    Where are you? Is there no insulation above the ceiling, either in the roof or on top of the ceiling? Is this space vented? I am not a pro, but if you do insulate like you plan (and I assume this will be the only insulation) I would think the first things you'll need to do is to ensure that you have ventilation over the insulation and very good air sealing in that ceiling, below the insulation.

  2. GBA Editor
    Martin Holladay | | #2

    You don't have much room to work with, so I disagree with John Klingel concerning ventilation. I don't think you have enough room for insulation as well as ventilation above the insulation.

    Your best bet is probably to install closed-cell spray polyurethane foam to create an unvented roof assembly. To ensure that the job is done well, you'll need access from below. That will require removing some of your ceiling. If you go this route, be sure to seal any existing vents.

    Another approach is to install rigid insulation on top of your existing sheathing. If you go this route, you'll also need to seal any existing vents. Of course, this approach requires you to replace the roofing, and that's not cheap.

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