Smart vapor barrier for finished basement ceiling?
I am finishing a 1300sqft basement in a house in climate zone 6. The basement is mostly underground on all sides, with 2″ XPS foam on exterior concrete walls. We insulated with 1″ XPS foam, 1 – 1.5″ spray foam, then the 2×4 metal stud wall with R13 Rockwool. We ended up with this configuration because I only learned about the need for continuous insulation after installing the 1″ XPS and the stud wall with 1-1.5″ space from XPS. A very knowledgeable guy on another site advised adding the spray foam and using the rockwool, which I have done. He also advised adding a smart vapor retarder (Membrain), which I have ready to install, but his instructions for using it only seemed to apply to the walls, he never mentioned the ceiling. Half of the basement is planned to use Ceilingmax drop ceiling, the other half drywall. We have R23 rockwool in the basement ceiling, and I have insulated the rim joists with 2″ XPS and air sealed, along with sealing the gap between the 1″ foam and the concrete at the top of the wall. It is a new contruction house with no moisture issues (yet). So my question is whether I should be installing the Membrain product in the ceiling as well? The purpose of the drop ceiling is to be able to access the pipes, junction boxes, etc, so seems like we’d eventually have to poke holes in the thing anyway.
On a side note, I’ve really appreciated the valuable info this site has already offered on this project, so thanks to all of you experts out there for offering your expertise so freely!
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