Is there a downside to spray foam insulation? An honest answer
Search for spray foam right now and you will find warning threads telling homeowners not to let any contractor talk them into it. We install spray foam for a living, and our answer to "is there a downside" is yes. Here are the real ones, the overblown ones, and how to tell which is which.
The real downsides
Cost is first. Spray foam is the most expensive of the common insulation types per unit of coverage, usually several times the price of blown-in fiberglass for the same area. For plenty of attics that premium buys real performance, because foam air-seals while it insulates. For plenty of others it buys nothing fiberglass would not have delivered.
Permanence is second. Cured foam bonds to what it touches. That is the point, and it is also why a bad install cannot be pulled out and redone cheaply. The material forgives nothing, so the installer matters more than with any other insulation type.
The cure window is third. Foam off-gasses while it cures, and the space needs ventilation and vacancy during that window. A crew that shrugs at this question is the wrong crew. We tell you the exact re-entry time in writing before we start.
And moisture is the one that produces the horror stories. Foam sprayed over a leaking roof deck or a damp surface seals the moisture in, and what had been a slow leak becomes hidden rot. This is an install failure, not a material failure, which is why our process inspects for moisture first and fixes water problems before any foam goes on.
The overblown ones
The "red flag" headlines mostly trace to the UK, where some mortgage lenders balked at homes with foam sprayed against old roof decking because surveyors could no longer inspect the timber. The practice that caused it, foaming over aged decking with no documentation, is avoidable anywhere: a correct install is documented, with foam type, depth, and the condition of what it covers on paper. In Arkansas we have not seen a properly documented residential install obstruct a sale.
"Can mold grow behind spray foam" is the other recurring fear, and the honest answer is that cured foam itself does not feed mold. The failure mode is the moisture one above: sealing over a wet surface. Dry surface, sound roof, no mold problem.
When we tell customers not to buy foam
This is the part a warning thread cannot give you: the cases where the right call is no.
- The attic just needs depth. If the air sealing is adequate and the insulation is thin, blown-in fiberglass gets you most of the comfort per dollar.
- The real problem is downstairs. Musty smells and humidity point at the crawl space, and the fix is encapsulation, not attic foam.
- The roof has an unresolved leak. Water first, foam later, no exceptions.
- The budget forces thin foam. Foam at half depth is most of the cost and a fraction of the benefit; better to do fiberglass properly than foam badly.
We sell all three services, so steering you to the cheaper one costs us margin and earns us the next thirty years of your house. That trade has worked for this family for decades.
How to vet an installer, including us
Ask four questions. Which foam and what depth, in writing. What happens if you find moisture. What is the re-entry time after spraying. Can I see the certificate of insurance.
Then read the reviews, not the star count: what customers describe is what the crew actually does. Ours are five stars across the board on Google, and the recurring theme is that we tell people the truth during the free estimate, including when the truth is that they do not need us.