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Does polyethylene installed in the ceiling cause any problems?

user-914555 | Posted in Energy Efficiency and Durability on

I live in Minneapolis Minnesota. Is there any problem with installing a polyethylene barrier in the ceiling? The insulation installer wants to use it to hold up the blow-in cellulose before the drywall goes up. I was planning on just using a vapor retarding primer/paint. One concern I have is that If I ever do have a leak in the roof I won’t know about it because the poly sheeting will block the water from reaching the drywall.

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  1. GBA Editor
    Martin Holladay | | #1

    In your climate, it is acceptable to install polyethylene. However, it isn't necessary.

    You're right that polyethylene in a ceiling can delay the discovery of a roof leak. But roof leaks have a way of showing up eventually -- trust me.

    It's essential that your ceiling have a tight air barrier. Pay particular attention to the gaps between partition top plates and drywall, gaps around electrical boxes, gaps at can lights, gaps at plumbing vent penetrations, and weatherstripping at attic access hatches.

    If the main purpose of the poly is to hold up the cellulose, you can choose an air-permeable membrane like InsulWeb instead of polyethylene if you want.

    If you don't install polyethylene, you'll still need a vapor retarder. Vapor-retarder paint is one option.

  2. user-869687 | | #2


    InsulWeb is better than poly for installing cellulose, because it holds in the fiber while letting the blowing air escape. Here's a very informative article about cellulose installation:

  3. Foamer | | #3


    Are you insulating an attic or cathedral ceilings? If it is an attic, your contractor can blow the insulation after the drywall is in. If you are dealing with cathedral ceilings, in my opinion you must vent between the cellulose and the roof deck. Dense packing cellulose against roof sheathing is a dangerous practice unless you have sufficient foam board insulation on the outside of the sheathing.

  4. user-914555 | | #4


    We are building a second story addition with one main shed dormer and two gable dormers. We are using dormers to minimize the overall height of the house. In fact the dormers will really have no attic space except where the ceiling drops down in the bathrooms and closets. The roof is constructed with 16” trusses 24” OC with 23” wide vent baffles. We did not plan to “dense pack” the truss space but rather blow in with settled depth at about 14”. We are using spray foam for walls, rim joist and any other vertical spaces.

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