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Community and Q&A

How can I prevent my roof from sweating?

Mr. T | Posted in GBA Pro Help on

Hey guys… I want to thank you in advance for your time and sharing your experience and professionalism. I live in Vermont. Upstairs, my roof is part of the wall structure. Last year, my roof sweat like crazy. We insatalled vinal in the eaves and proper vented the roof to the attic space. My issue seems to be in the valleys. Since they dont stretch to the eaves, I am unsure how to get ventilation. Right now, there is proper vent in there with fiberglass insulation below. As you can well imagine, the venting isn’t cut perfectly and the insulation butts up tight. Will this work?

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  1. GBA Editor
    Martin Holladay | | #1

    What do you mean when you say that your roof "sweats"?

    Are you talking about metal roofing?

    I assume that this "sweating" is some type of condensation. Where is the condensation visible?

    Where is your ceiling insulation -- on your attic floor? Or do you have an insulated sloped roof assembly?

  2. Mr. T | | #2

    Hey Martin... I do have a tin roof... and yes... I meant that I have an insulated sloped roof. With valleys to contend with. The condensation is obviously from a drastic temp difference. I'm not really sure what the best way to insulate this area is in this circumstance. I apologize for the unsavvy lingo. Any suggestions...? And thanks:)

  3. GBA Editor
    Martin Holladay | | #3

    From top to bottom, how did you build your roof?

    For example:
    Metal roofing, 2x4 purlins, asphalt felt, plywood sheathing, air gap, Proper-Vent, fiberglass batts, drywall.

    I just made up that assembly -- yours is probably different. Tell me how you built your roof.

  4. Mr. T | | #4

    Okay... From the top down I have metal, then 2x4 ribbing on top of 2x6 rafters with proper vent than insulation. The upstairs is still unfinished because of the condensation issues. ( which at times have created a lot of dripping water)

  5. GBA Editor
    Martin Holladay | | #5

    Since you built a roof without a layer of solid sheathing, it's going to be hard to insulate. The type of roof you describe works well for a barn, but not for a house.

    Your roof has no air barrier. That's a problem. You also forgot to install roofing felt under your metal roofing. That's another problem. (The whole point of the roofing felt is to handle the condensation.)

    The best way to fix the problem is to remove the roofing panels, install plywood roof sheathing, and then re-attach the roofing panels. But that is a lot of work.

    Another possibility is to install closed-cell spray foam on the underside of your metal roofing. That might work, but it would be expensive, and it would mean that replacing the roofing when it finally wears out would be a nightmare.

  6. Mr. T | | #6

    Okay. Well thank you very much. Sounds like I've got plenty to do in the spring.

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