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Is there a good method for insulating a ceiling with strapping?

rnasella | Posted in Energy Efficiency and Durability on


I am in the process of removing a bathroom ceiling due to a large crack that spans the entire room.

I am going to reinstall a new ceiling using 1×3 strapping because I believe the current ceiling failed due to either joist flexure or the crown of the joist is facing the wrong direction. I believe by strapping and shimming this should protect the new ceiling from failing in the same manner.

The ceiling is adjacent to the attic above and therefore needs insulation . For simplicity I was going to use fiberglass batts with kraft paper and staple the kraft paper to the joist faces.I understand the insulation must come in contact with the backside of the drywall in order to be most effective. However, the strapping will not allow it to do this due to a 3/4″ air gap caused by the thickness of the strapping. From reading some people had mentioned blown in insulation for situations like this, however the area that needs to be insulated is very small (5′ x 9′) and I feel that renting a machine just to blow in insulation above this area seems to be not worth the trouble.

A couple of ideas I had:

Install 3/4″ thick foam insulation boards between the strapping from the bathroom side then place unfaced batts on top of foam board in between the joists in the attic. I am not sure how this works with the vapor barrier. Would I need to add a plastic vapor barrier or does the foam provide a good enough barrier? Also, would there be any negative effects of layering two different types of insulation materials on top of each other?

Spray foam in all the cavities until the 3/4″ in thickness is filled and lay fiberglass batts on top. Same concerns as above.

Pull apart the fiberglass batts and fill the 3/4″ spaces with this material leave the kraft paper and staple this to the strapping. Apply unfaced fiberglass on top of this layer in the attic. I would think this would be the most time consuming due to the amount of cutting required to make the 3/4″ thick batts, however it would be the same material layered on top of each other.

Leave 3/4″ space open.

Do any of these ideas sound viable? Or is there another method that would work better?

On a side note. I have seen a lot of debate about using a plastic vapor barrier on a bathroom ceiling. Some say this is necessary and much better than kraft faced paper, others say it may cause moisture buildup and eventually mold because the plastic does not allow the moisture to pass through where the kraft paper does.

I appreciate any suggestions and thoughts as I can tend to overthink these things :).

Thank You.

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  1. user-2310254 | | #1

    Rich. Is the crack at a joint between two sheets of drywall? If so, the joint may not have been properly treated.

    Also, does the drywall move if you press against it? If so, adding screws may be part of the solution to this particular problem.

    I would check out these other possibilities before removing the drywall. Also tell us where you live so we can offer a location-specific response to your insulation question.

  2. rnasella | | #2

    Hi Steve,

    Thank you for the response. I live in Massachusetts which is considered a zone 5 climate zone.

    You are correct in your assumption. The crack is between 2 pieces of drywall. However, is it still sagging in that area. I originally tried to pull back the drywall to the joist by using screws, but it did not seem to make a difference. In some areas the gap between the 2 pieces of drywall is large (1/4") and there is not tape at the seam. Also, the rest of the ceiling is a mess. It is textured, but that is starting to peel off and there is a large hole leading up to the attic above the shower. This was uncovered after a false ceiling was removed above the shower. The original installation was a tiled ceiling above the shower, but somewhere down the line someone decided to remove the tile and cover this area with the lowered ceiling. The ceiling was dropped by about 1-1/2' which really closed off the shower space especially in this small of a bathroom. I had decided to remove this because it was really closing off the bathroom above the shower. What was remaining was the original ceiling where the tiles were once removed. The remaining ceiling is all torn up from the tile removal.

  3. GBA Editor
    Martin Holladay | | #3

    Q. "Would I need to add a plastic vapor barrier or does the foam provide a good enough barrier?"

    A. You don't need interior polyethylene (although in a Massachusetts bathroom, polyethylene won't hurt). You can add strips of 3/4-inch-thick rigid foam between the strapping as you suggest if you want, paying attention to airtightness as you proceed. (each rectangle of rigid foam should be sealed at the perimeter with caulk or canned spray foam). Once this is done, you could (optionally) also install a layer of polyethylene on the interior side of the strapping.

    Q. "Would there be any negative effects of layering two different types of insulation materials on top of each other?"

    A. No.

  4. rnasella | | #4

    Hi Martin,

    Thanks for answering my questions. I am still a little confused by the vapor barrier. Wouldn't the foam insulation act as a vapor barrier and by adding the polyethylene create a double vapor barrier? From what I am reading a double vapor barrier should be avoided.

    Thanks Again!

  5. GBA Editor
    Martin Holladay | | #5

    Double vapor barriers are just fine in this case. To understand why, you may want to read this article: Worries About Trapping Moisture.

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