If you've searched "spray foam smell" at midnight, you've seen the stories: houses that still smell weeks later, foam pulling away from rafters, owners paying to tear it all out. They're real. A peer-reviewed review of ten households with faulty foam retrofits found every family reported odors and irritation symptoms (PubMed, 2014). In news coverage of one Florida case, an inspector found cheaper open-cell foam hidden under a closed-cell skin.
Those stories don't mean spray foam is a bad material. They show how much depends on who installs it and how. So instead of another pros-and-cons list, here's the interview we'd want every homeowner to run, with what good and bad answers sound like.
"Which exact product are you spraying, and can I see its safety data sheet?"
Good answer: A brand and product name, open-cell or closed-cell, and the SDS handed over without hesitation.
Red flag: "Our usual foam." If they won't name it, you can't check it.
"How long do we need to stay out, and what is that based on?"
The CPSC recommends that occupants vacate during installation and for at least 24 hours after, and the EPA says re-entry time should be agreed with the contractor before the job.
Good answer: A specific number of hours for this product, from the manufacturer's guidance, plus how they'll ventilate.
Red flag: "You can stay home, it's fine."
"How do you check the mix ratio and spray temperature on site?"
Two-part foam has to meet in the right proportions at the right temperature. Off-ratio foam is the most common root cause of lasting odor and shrinkage.
Good answer: They check equipment pressure and temperature, spray a test shot before each job, and keep a log.
Red flag: Nobody on the crew can explain it.
"How thick is each pass?"
Good answer: Closed-cell goes on in limited-thickness passes, with cooling time between them, as the manufacturer specifies.
Red flag: "We do it all in one shot to save time." Overly thick passes overheat and can crack, shrink, or scorch.
"What will cover the foam afterward?"
In living spaces, and often in basements and attics, building codes generally require foam plastic to be covered by a thermal barrier (typically ½" gypsum board) or an approved ignition-barrier coating, depending on the space and product.
Good answer: They name what the code requires for your space and include it in the quote, or tell you exactly who is responsible for it.
Red flag: Bare foam left in a finished basement with no mention of a barrier.
"Open-cell or closed-cell here, and why?"
Closed-cell is denser, adds rigidity and slows vapor. Open-cell is softer, cheaper per inch and better at sound damping. Neither is "better" everywhere. Rim joists and below-grade walls usually favor closed-cell, while some roof assemblies suit open-cell with the right vapor control.
Good answer: A reason tied to your assembly, such as moisture, roof type or space.
Red flag: One product recommended for every surface.
"What happens to the HVAC system while you spray?"
Good answer: It's shut down, and vents in the work area are sealed so overspray and vapors don't travel through the house.
"If I still smell it next week, what do you do?"
A mild odor right after curing is common. A strong smell that persists, or eye and throat irritation, is not something to live with.
Good answer: A written process: return visit, inspection, and remediation if the foam is defective.
"Who closes up the wall after you leave?"
This is the question people forget. Foam is rarely the last step. Someone has to install the board, finish it, and match the existing walls. When three different trades share that job, gaps open between them.
Good answer: One accountable company, or a clear hand-off with dates.
- ☐ Product name + SDS in hand
- ☐ Written re-entry time and ventilation plan
- ☐ How they check mix ratio and temperature on site
- ☐ Pass thickness per manufacturer
- ☐ Thermal or ignition barrier included or assigned
- ☐ Open- vs closed-cell reasoning for each area
- ☐ HVAC shut-down and vents sealed
- ☐ Written odor/defect follow-up process
- ☐ Who finishes the walls, and when
Where Smooth fits
We're a licensed and insured insulation contractor that also hangs board and plasters. Ask us these nine questions on your estimate visit. Questions 5 and 9 are why many New England homeowners and general contractors use one crew from foam to finished wall.
Quick answers
How long should I stay out of my house after spray foam?
The CPSC recommends vacating during installation and for at least 24 hours after. The exact time depends on the product and ventilation, so get it in writing from your contractor before the job.
Is a lingering spray foam smell normal?
A mild odor that fades after curing is common. A strong or persistent smell, or eye and throat irritation, can indicate an installation problem and should be inspected.
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