Spray Foam Insulation and Water-Damaged Buildings: Persons with CIRS, Beware!
- Christine Daecher, DO
- Feb 18
- 4 min read
Updated: 7 days ago
There has always been something about spray foam insulation that hasn’t sat right with me.
It’s a relatively new way of insulating homes. It has not stood the test of time the way traditional pink fiberglass insulation has. And my recent experience with spray foam — and the significant water damage that followed — is a cautionary tale worth sharing.
Before you fall for the marketing, please read this, especially if you or someone in your family suffers from Chronic Inflammatory Response Syndrome (CIRS).
The History of Spray Foam Insulation
Spray foam insulation was initially developed in the 1940s. It began being applied in commercial buildings in the 1960s and did not move into residential construction until the late 1970s. Its widespread use in homes didn’t occur until the 1990s and early 2000s.
In other words, this is not a century-old building practice. It is relatively modern.
Today, spray foam is created by mixing methylene diphenyl diisocyanate (MDI) with a resin blend. Once sprayed, it expands and cures into either:
Open-cell foam, which uses water as the blowing agent
Closed-cell foam, which uses HFO (hydrofluoroolefin) blowing agents
Once cured, it is essentially a plastic. You will hear that spray foam is “mold resistant.” That is partially true. It is not organic and does not provide a food source for mold. Closed-cell foam, in particular, has fewer open air pockets and is less likely to hold moisture within the foam itself. But here is the part that is rarely discussed:
just because the foam itself does not grow mold does not mean it cannot contribute to a water-damaged building. Do not fall for simplified marketing material.
My Story
I recently experienced a significant water damage issue that was made much worse because of spray foam insulation. The property in question is elevated, eight feet off the ground on stilts. In coastal Georgia, I generally prefer this type of structure. It avoids crawl spaces that trap airs and moisture, and slabs that may or may not have adequate vapor barriers. Raised homes allow airflow underneath and do not tend to draw air near the soil into the structure. (Air near the soild has more bacteria and mold particles.) It will never experience a catastrophic storm surge or groundwater flood.
We noticed water staining on the drywall casing on the underside of the home. Initially, it appeared to be a minor plumbing leak that may have sealed itself.
But something didn’t sit right with me. Once we removed the spray foam insulation from beneath the subfloor, the real problem became obvious. The foam had trapped water against the wood subfloor. Instead of dripping down and revealing itself, the moisture spread laterally along the subfloor for an extended periord of time, leading to significant rot beneath an entire master shower floor. The damage was extensive.
Had this home been insulated with traditional fiberglass batt insulation, the leak likely would have been discovered much earlier. Fiberglass does not adhere tightly to the subfloor. It does not trap water against wood in the same way. Gravity would have done its job. The leak would have declared itself. Instead, the foam masked it.
The Larger Problem with Spray Foam
When spray foam is used in attics — particularly in humid climates — additional risks arise. Problems occur when there are even small unsealed areas where airflow and humidity can enter. In my opinion, it is nearly impossible to achieve a perfectly sealed envelope over time. Buildings move. Materials age.
Spray foam essentially eliminates traditional attic ventilation. I grew up in Pennsylvania, where attics are vented to allow airflow and humidity to escape freely. In the South, the climate is more humid year-round. The building science philosophy shifts toward preventing outside humidity from entering — but that does not eliminate the reality that moisture intrusion can still occur. And when it does? Spray foam can hide it.
If there is a roof leak, the water may become trapped between the roof sheathing and the foam. The leak can persist for months — or even years — without visible evidence. By the time it is discovered, the damage can be substantial. Again, the foam itself is not a substrate (food source) for mold. It is plastic. But it can create the conditions that allow rot and mold to thrive in adjacent wood.
That is not low risk.
Where Spray Foam Does Make Sense
I am not saying spray foam has no place in residential construction. There is a very reasonable use case for it — sealing small cracks and penetrations. I am talking about the homeowner buying a can of Great Stuff at the big box store and sealing around plumbing penetrations or gaps in framing. That is targeted air sealing.
Whole-home encapsulation, in my opinion, is a different category entirely — and one that deserves far more caution than the marketing suggests.
In commercial settings, particularly when spray foam is applied directly to metal walls or roofing systems, it may be a more reasonable choice. Metal is not an organic substrate and does not support mold growth. In those applications, the risk of trapping moisture against a mold-susceptible material like wood is significantly lower.
Final Thoughts
Spray foam looks clean. It looks “zipped up.” It looks modern.
But newer does not always mean better.
When building in humid coastal environments, the question is not just insulation value. The question is: what happens when water inevitably finds its way in?
Because it will.
And when it does, you want it to reveal itself — not hide behind plastic.
Read more about one homeowner's spray foam nightmare:
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