Find old post on hot roof insulation
Early in 2018 you had a post on how to insulate a hot roof. I asked for details in mid-2018 and didn’t get an answer. So I’m asking again.
The article walked the reader through how to create a vapor barrier, and that’s the detail I need explained.
Background: house was built in 1895. Back gable was added probably in 1896. The main house has an attic (now completely insulated). The back gable has blown-in cellulose because that was the simplest way to get insulation into a steeply roofed area where the ceiling is attached directly to the rafters.
As you can imagine, in more than 120 years, the plaster has deteriorated. I’ve removed the crumbling plaster and repaired the rest.
How do I create a vapor barrier over the wood lath so I can put up drywall on the ceiling? What specs must be followed?
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Replies
What DOE climate zone?
Is any of these the article you're remembering?
https://www.finehomebuilding.com/2015/11/11/insulating-unvented-roof-assemblies
https://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates
https://www.greenbuildingadvisor.com/cad/detail/unvented-roof-for-cold-climate-cathedral-ceiling-asphalt-roofing
https://www.greenbuildingadvisor.com/article/can-cellulose-be-used-in-an-unvented-roof
https://www.buildingscience.com/sites/default/files/migrate/pdf/BA-1001_Moisture_Safe_Unvented_Roofs.pdf
Maybe this? How to Build an Insulated Cathedral Ceiling
Along with the location of the house, some other questions:
It sounds like the ceiling is currently open. Is the cellulose insulation still in place?
Also, if the cellulose was a retrofit, the roof is probably unvented. Is that correct?
Thank you, Dana Dorsett and Brian Pontolilo!
I think the article I read is No. 4 on Dana Dorsett's list. Seems familiar.
I'm not sure it addresses the concerns of how to deal with dense-pack cellulose insulation directly up against the roof decking. Seems there was supposed to be one of several other materials before the cellulose. I did contact a roofing company about reroofing the back gable. They estimated a roofing job at $7k but $15 k if I wanted them to add rigid foam boards before shingling. So I think I'm out of luck.
Brian Pontolilo, the house is located in Kalamazoo, MI. Although the maps show it as needing 38-R, local insulation people and the local gas and electric company recommend 49-R.
The ceiling is currently open. The cellulose insulation is still in place. The roof is unvented. In fact, before I surreptitiously had vents put in, the attic over the main house was unvented.