GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Double Vapor Barrier (Spray Foam Odor Remediation)

VkTjnQAEmn | Posted in General Questions on

First off, I want to say THANK YOU to everyone who contributes to this site. It has been a great resource for me over the last couple of months, and knowing how precious time is, I really appreciate the fact that you spend it here.

Without getting into all of the details right now, let me just say that I had closed-cell foam applied to the upper half story of my 1939 1.5-story (zone 6A) stucco home about six weeks ago, from the rim joists to the peak and on the two end walls. (The room was gutted at the time.) The job resulted in some very smelly (fishy) foam, and the contractor has since tried a few methods to remediate the odor… such as aggressive ventilation, heating up the room, and applying a few coats of a Zinsser primer/sealer. Although that last one cut the odor to about 50% of what it originally was, it was still quite strong and had me concerned about long-term containment (and when it gets hot here again).

A few days ago, the contractor hung six-mil poly sheeting around the room (horizontally across the narrow ceiling, down the slants, vertically on the knee-wall framing, and on the end walls). This has pretty much contained the smell, but it has me thinking about the risks of double vapor barriers… or at least the problems with a vapor barrier on the conditioned side of a room. The foam is applied between 3-3.5″ on the slants and end walls, and more like 4.5″ or more in the peak and crawl-space areas, and I know that it’s a vapor barrier as well when applied greater than 1″ thick..

So… in a nutshell, I’m wondering if I should be concerned about moisture, mold, and breathability of the room if I go ahead and sheetrock the space? The rest of the house still has the original insulation, which is likely either fiberglass or those old-style sewn-together sheets of paper.

Thanks in advance for your help!!

P.S. – I’ve read Martin’s great article on spray foam issues, as well as several of the other Q&A threads on the subject. I can certainly provide additional details about my experience if necessary, but my primary initial goal was to get some thoughts on the vapor barrier questions.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    I don't think the polyethylene will cause any problems with condensation or drying -- assuming the spray foam was installed well enough to create an air barrier.

    However, I would certainly be leery of accepting fishy-smelling foam in my house. It's possible that hot weather will bring the smell back to haunt you. If you have smelly foam, you probably want to negotiate with the spray foam contractor and the spray foam manufacturer to have the smelly foam removed from your house. Putting it behind a plastic bag is not a good solution.

  2. VkTjnQAEmn | | #2

    Thanks very much for the response. To close the loop, I wanted to let you know that the foam was ultimately removed and sprayed again (successfully this time). Between my misgivings about the plastic and the fact that some odor was still making its way into the main living area of the house, I decided that removal was the only option. (Your response above helped to push me over the edge, so thanks for that as well.) It took them about a week to do the removal work, and it was pretty painful for all parties, but I'm convinced it was the right thing to do.

    For anyone else who might ultimately read this thread because of smelly foam issues in their home, take my advice... bite the bullet and have it removed. If you have a persistent and strong fish/urine odor that does not fade after a few days, don't try to cover it up. (You'll know if you have an issue, trust me.) Read the related blog post here from Martin to confirm, and then do what needs to be done.

  3. GBA Editor
    Martin Holladay | | #3

    It sounds like you made the right decision. Thanks for coming back to report on the work.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |