Vapor barrier on ceiling?
JyKChUWn3u
| Posted in Energy Efficiency and Durability on
We are building a new home in NW Montana, zone 6. We have a great room with a vaulted ceiling and a vented roof above. Going to use cellulose to r49 above great room. I want to make sure that I get the ceiling profile right. I have been told to put poly on ceiling then osb or plywood and lastly the metal we want to use for the interior finish. Will this work without causing moisture problems?
Any draw backs to using metal roofing on the interior ceilings as finish?
Thanks
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Replies
Rob,
First of all, if you are insulating a sloped roof assembly with cellulose, you need to include vent channels between the top of the cellulose insulation and the roof sheathing. I hope you are planning to do that. (For more information on venting cathedral ceilings, see How to Build an Insulated Cathedral Ceiling.)
Second, building codes do not require the installation of an interior vapor barrier; all they require is a vapor retarder. Your proposed ceiling assembly already includes at least two vapor retarders: the metal roofing you plan to install as your interior finish material is a vapor retarder, and so is the OSB that you intend to install on the interior of your wall. So you don't need interior poly. It's better to leave out the poly.
There's nothing wrong with using metal roofing as your interior finish material, if you like the look of it.
But where's the air barrier? Metal roofing as the interior finish material will have thousand gaps and cracks, so your OSB/plywood substrate had better be tightly caulked and/or taped first.
Martin and James,
Thanks for the info. I will certainly seal the plywood joints as you suggested. For what it is worth, the discussions and information here on GBA is unparalleled. We are building our own "pretty good" dream home with the help of GBA at each stage.
Back to driving nails.
Thanks for your help.