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Community and Q&A

How to insulate tiny hot roof

AZOgram | Posted in General Questions on

I live in Michigan. We just survived six months of snow. It’s forecast to be 80 next week. Humidity in summer is very high. Those are the unchangeable factors.
I’d like to insulate the roof in my bedroom closet. The house went on the tax rolls in 1896, when insulation wasn’t a big concern for the builder.
I had dense pack cellulose blown into the walls. A pro did the attic over the two-story part of the house; another company blew in cellulose into the roof of the 1 and 1/2 story part. All parts of the ceiling in that section are lath and plaster.
All the bedrooms are in the two-story part of the house, but this closet (there are two in the whole house) is in the 1 and 1/2 story part. When you open the closet door, the sloping roof of the two-story part blocks part of the entry.
The ceiling in this closet is roughly 6-feet long by 3-feet wide. It’s maybe a 30 degree angle. The previous owner didn’t fix the cracked ceiling plaster but installed drywall over it. Amazing crop of black mold on both sides of the drywall. I’ve removed what I can, but have a bit more to go. I suspect there’s mold I can’t see because I have a persistent cough that goes away when I’m away from my house even overnight.
My plan is to remove the last of the drywall in the closet. Then what?
Thanks for all advice.

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Replies

  1. user-2310254 | | #1

    Just guessing, but it sounds like you have leaky house with significant wintertime stack effect. (Warm air rises during the winter and condenses when it hits your cold roof.) You might want to check with your local utility and see if they have an energy conservation program that would help you to hire a crew to air seal your home. What kind of foundation do you have?

  2. AZOgram | | #2

    The crew that sealed the attic was one of a handful statewide that is approved by the local utility. They did an excellent job of sealing off the stack effect of having an interior stairwell that runs from the second floor to the basement. I'm not talking about that. That's the three-gable portion of the 1896 house. I'm talking about the story and one-half section that abuts the two-story, three-gable portion. If I were to add photos, they would take up too much room on this forum. I'm dealing with, in essence, two types of construction butted together. I just want to know how to insulate the 6X3 closet in my bedroom. It's 1:12 a.m. I'm awake because it's hard to breathe in the bedroom, probably due to mold. Mold needs food and moisture (I read this blog for years before asking the question). If I get rid of the drywall, I get rid of a food source. What I want to know is how to block out moisture and insulate well so I don't kill my roof.

  3. GBA Editor
    Martin Holladay | | #3

    Azogram,
    There is only one way to insulate an unvented roof assembly from the interior, and that's by installing an adequately thick layer of spray foam on the underside of the roof sheathing. Make sure that the sheathing is dry on the day the work is performed.

    You have two choices: You can either get all of your R-value from the spray foam -- you want R-49 in your climate zone, so that would mean about 7.5 inches of closed-cell spray foam -- or you can follow the flash-and-batt method.

    For more on flash-and-batt, see Flash-and-Batt Insulation. If you are in Zone 5, the flash-and-batt approach requires a minimum of R-20 from the spray foam layer (about 3 inches); if you are in Zone 6, the flash-and-batt approach requires a minimum of R-25 from the spray foam layer (about 4 inches of spray foam).

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