Recently installed foam insulation is separating from joists. Is it an installation problem, or typical of the product?


Recently installed foam insulation is separating from joists. Is it an installation problem, or typical of the product?

Asked by Tommy Sullivan

I'm nearing the end of a substantial remodel in which I had closed-cell foam installed in the entire home. I recently heard load popping noises but couldn't find the source of the noise. Today one of my subs was in the crawl space and pointed out that the foam insulation between the floor joists was separating from the joist, leaving gaps large enough to reach your hand alongside the joist, all the way to the subfloor. Is this an installation problem, or the nature of the (very expensive) product?

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Raymond Pruban's picture

I am a green builder and have been installing closed cell foam for about five years now.

Our company owns its own closed-cell equipment and therefore we have a fair amount of experience, although I would not claim to be an expert.

An art and a science

I can tell you that spraying closed cell foam is a science and an art all at the same time. Everything affects the outcome.

Some of the variables include

  • the equipment
  • the outside temperature
  • the temperature of the surface you are spraying
  • the temperature of the foam at the nozzle
  • the temperature of the foam in the truck
  • the humidity in the air
  • the moisture content in the wood or surface
  • and the list goes on and on and on.

The average career of a person in the closed cell spray business is like two to three years.When I subcontract, I only use one of two suppliers that have more than ten years experience.


Closed cell foam will not adhere to water (e.g., wet wood). If the wood is wet when the foam is installed, it will tend to not stick and cause shrinkage.

Also, if the equipment or spray gun malfunctions, it is possible to get a weirdmixture that shrinks as well.

I have seen some products on the market that expand more when spraying but also have a tendency to shrink later.

Given all of the above, I have seen some minor shrinkage which is combination all the variables I have mentioned.

  • Minor shrinkage would be like 1/16 over a 24" width.
  • I have never seen what sounds like shrinkage of 1/2 inch over the total spray depth, which is very concerning.
  • In my estimation, the problem definitely needs to be fixed.

Get a second opinion

You will want to get a second opinion by someone who can make a proper visual inspection, but the contractor should come back and touch up those areas.

If you sprayed closed cell foam in the wall, you may want to open at least one or two areas to conduct an inspection to verify the problem is limited to the crawl space.

A bigger issue than shrinkage?

When closed cell is sprayed properly, the surface will be hard and very difficult to break.

If the closed cell product is flaking or easily falling apart, you have bigger issues than just the shrinkage to contend with.

For more information:

Read "Is there a standout spray foam insulation brand? Or one to avoid?" a Q&A by David Edwards.