The Folly of Foam

For those who are interested in creating energy efficient homes and additions, there is something incredibly seductive about spray polyurethane foam (SPF), commonly called spray foam insulation.  In its closed-cell form it offers both unparalleled r-value performance as well as a permeability rating that keeps wall and ceiling cavities dry and safe from the mold and moisture issues that can affect energy-efficient homes.

But is that seduction misdirected?  Does spray foam insulation live up to the hype?  At Decumanus Green, we approach SPF with a healthy dose of skepticism.  And here is why.

First of all, there are compelling reasons for doubting the advertised r-value of SPF, and its real-world performance is a hotly debated topic at most building conferences and green building websites.[1]  Moreover, there is growing argument against SPF from those who see carbon emissions, and not energy consumption per se, as the real enemy in the climate warming war.[2]  

But there is yet another issue that we have seen in our experience with foam that makes us not only avoid foam but to actually fear it.  This fear has led us to stop using it altogether in ceiling and wall cavities, and has limited our use of it in crawlspaces and basements.

Recently we were involved in two projects that made use of SPF. These were projects led by other builders for whom we were acting as one insulation contractor among several on the job.  SPF was chosen for certain areas of a job precisely because of the positive characteristics listed above.  However, in both cases the miracle of SPF’s versatility turned into a nightmare built on its fragility.  Spray from insulation is fragile.  It’s the Donald Trump of insulation products. What I mean by that is that it is high-maintenance to the extreme, and when it does not get its needs met, tantrum-like, it creates havoc for homeowners.

Elsewhere in this blog, I have written about the advantages of off-site manufactured homes.[3]  I spoke of the benefits of assembling components of a home in a factory setting that is free from the forces of chaos that seem to threaten every job site.  Precision and accuracy are far easier to achieve in a factory than on a work site. SPF needs that kind of precision in manufacturing, and yet it is manufactured on the job site, where environmental control is illusive at best.  The manufacturing process that converts chemicals stored on a truck into a well cured insulation product in a house demands precise temperature control of chemicals and building surfaces, precise aging and mixing of chemicals, and precise rate and depth of spray application. 

When any of those manufacturing variables diverges from requirements, bad things happen.  On the jobs we have been involved with we have seen issues ranging from somewhat problematic to wildly destructive.  The outcomes can be seen in the accompanying pictures.


Some manufacturing variable was clearly off in filling of this wall cavity.  The shiny, drippy appearance of sections of the foam are a telltale sign of a poor application process.

At the same wall job, gaps opened up as the spray foam cured and shrank away from framing members.  The consistency of the foam is better here, but clearly there are still problems.  Gaps in insulation like this not only reduce the wall assembly’s r-value, they also can be the source of serious moisture, mold and rot issues down the road.  Fortunately for the client, the spray foam contractor recognized and acknowledged the problem and redid the insulation, this time with better results.


This house was built by an extremely conscientious owner/builder.  He did his research and made every effort to do things right.  I was called in as a consultant for the insulation work.  The builder/owner went with vented ceiling cavities with closed-cell spray foam insulation in his cathedral slopes.  This should have been a bullet-proof assembly against ice-damming and uneven snow melt on the roof.[4]  But as the pictures show, it was not.  Somehow, warm air was reaching the bottom of the roof decking and melting the snow in a very clearly marked pattern. Something had gone horribly wrong.

It was the spray foam!

Incredibly, the spray foam had shrunk with such force that it actually pulled apart framing members, which created a pathway for warm air to bypass the insulation and travel to the bottom of the roof deck and melt snow.  This not only created ice dam problems, but also threatened the structural integrity of the roof assembly.  Once again, the spray foam contractor was a professional and put his own time and money into fixing the problem to the client’s satisfaction.  The house has made it through one winter without issues.  The story ends well, but the stress and physical displacement that the owner/builder went through is something that I will not risk subjecting my clients to. 

Thankfully, there are better ways to insulate ceiling cavities and we have done many of them without any failures.  

[1] (

[2] King, Bruce, The New Carbon Architecture, BC, Canada: New Society Publishers, 2017. Pp 85-99.


[4] For details on a bullet-proof roof assembly, see my previous blog post: