Spray Foam Insulation Problems:
Odor, Exposed Foam, Roof Decks, and What It Hides
Spray polyurethane foam insulates and air-seals in one pass, under roofs, in walls, and on crawlspace walls. Installed well, it works. Mixed wrong, left exposed, or sprayed over things that need to be seen, it causes problems nobody can easily undo.
Spray foam is the one insulation that also air-seals. Two chemicals get mixed at the spray gun, expand, and harden in place against the framing. In some Portland-area remodels and newer houses, that’s what’s under the roof deck or on the crawlspace walls instead of fiberglass or blown cellulose.
When it goes in right, the house is tighter and quieter. When it doesn’t, the problems are hard to see and harder to fix.
Open-cell and closed-cell are different materials
They come out of the same kind of gun, but they behave differently.
Open-cell foam is soft and light, about R-3.6 per inch according to the Department of Energy’s Building America spray foam guide. At 5 inches thick it still lets water vapor through, and the guide notes it “will also absorb and hold liquid water.”
Closed-cell foam is dense and rigid, about R-6 per inch. At 2 inches it passes less than 1 perm of vapor, which makes it a vapor retarder.
The difference shows up most under a roof. Joe Lstiburek of Building Science Corporation has written about moisture building up in the roof sheathing above open-cell foam, collecting near the top of the attic, in several climates. His point: attics insulated that way have to be treated as conditioned space. Closed-cell foam keeps indoor air away from the sheathing. Neither one is right for every roof. The design has to match the house.
When the foam isn’t mixed right
Two-part spray foam is made on site. If the ratio, temperature, or mixing is off, a 2017 paper published by ASTM says the foam “may fail to completely cure.” The tell is a persistent fishy odor, mostly from the amine catalysts.
EPA’s guidance on spray foam says isocyanates, the reactive chemical in the mix, can cause skin, eye, and lung irritation, asthma, and sensitization, and that some symptoms show up hours later. The CPSC tells homeowners to leave the house during installation and for at least 24 hours afterward, and says some have reported smells and breathing problems that continued long after.
If the smell doesn’t go away:
- Call the installer first, and ask for the product name and the installation date.
- Report it at SaferProducts.gov, which is what the CPSC recommends.
- Consider an indoor air quality consultant.
There’s no easy fix after the fact. The CPSC says there are no standard processes for removing or remediating misapplied foam.
Exposed foam and the thermal barrier rule
Foam plastic burns. The residential code that Oregon and Washington both build on, the 2021 International Residential Code, requires foam plastic insulation to be separated from the inside of the house by a thermal barrier, such as half-inch drywall (section R316.4). Oregon’s 2023 residential code and Washington’s code, in effect since March 2024, are both based on that edition.
There’s an exception for attics and crawlspaces that people enter only to service utilities. There, a lighter ignition barrier can be used instead.
The common miss is a space that stopped being “service only.” An attic converted to storage, a bonus room, a basement wall finished halfway: foam that was fine behind a closed hatch is now exposed in a room people use. The same goes for rigid foam board. One foil-faced board Russ found exposed in an attic room carried a printed warning from its maker that it has to be protected from ignition sources by a thermal barrier.
The other spray foam: a can from the hardware store
Most of the foam Russ writes up isn’t insulation at all. It’s one-part expanding foam from a can, used to stuff a gap.
His reports show where it turns up. Around a refrigerant line where it enters an air handler, where it can become brittle, trap moisture, and get in the way of service; a grommet or duct sealant is the right part there. Piled around a second-floor bathtub drain where it passes through the floor. And around the base of a water heater tank, where the cause wasn’t clear.
The bathtub one is the reason he writes these up. As his report put it, “Spray foam is often applied to conceal unsealed floor openings or active/past plumbing leaks.” It can also hold moisture against the subfloor. He recommended a licensed plumber remove the foam and look at the drain fittings and the wood around them.
Real Inspection Photos
Foam From Russ's Inspections
Foam insulation left exposed, and can foam used to fill gaps, from Russ's reports.
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Foam board left exposed in an attic room. The maker's printed label says it must be protected from ignition sources by a thermal barrier. -
Expanding foam around a bathtub drain. Russ recommended a plumber remove it and check the fittings and subfloor underneath. -
Can foam sealing a refrigerant line into an air handler. A grommet or duct sealant is the right part there. -
Rigid foam boards on crawlspace walls, one hanging loose. Boards like these cover the concrete an inspector needs to see. -
Foam around the base of a water heater tank. The cause wasn't clear, so Russ recommended further evaluation.
What foam hides from an inspection
An inspection is visual. Foam on the underside of a roof covers the sheathing, the rafters, and any nail heads that would show a leak. Foam on crawlspace walls covers the concrete. In one Lake Oswego crawlspace, Russ noted rigid foam boards on the foundation walls with some panels loose, and pointed out that in a vented crawlspace they add little and can hide cracks, water, or pests.
The Oregon standards of practice don’t require an inspector to move or disturb insulation, and nobody should be cutting into a seller’s foam. What Russ can report is:
- Where the foam is and what type it appears to be
- Foam left exposed in rooms, storage attics, or garages
- Gaps, shrinkage, or foam pulling away from framing
- Staining, moisture, or damage he can see at the edges
- A lingering odor
The paperwork helps more than anything a buyer can see. Ask for the installer’s name, the product, the install date, and the insulation certificate if one was posted. In Oregon, anyone paid for construction work has to be licensed with the CCB, and Washington requires contractors to register with L&I, so the installer should be easy to look up.
Spray foam works when the type fits the house, the mix is right, and it’s covered where the code requires. Ask for the installer and product records, watch for exposed foam in rooms and storage attics, and treat a lingering fishy smell as a question for the installer.
For other insulation Russ runs into, see vermiculite attic insulation and faced fiberglass insulation installation. The attic inspection guide covers what gets checked up there, and what to look for in the crawlspace before you make an offer covers the space under the house. To book an inspection in the Portland metro or Southwest Washington, schedule online.
Spray Foam Insulation FAQ
