Spray Foam Smell: What's Normal and What Isn't

Where spray foam smell comes from

Spray foam is made from two liquids that react on site, and the reaction is fast: the foam feels firm within minutes. EPA cautions that foam can be tack-free and still contain "unreacted SPF chemicals," and that curing time depends on the product, thickness, temperature and humidity.

The odor comes from the volatile ingredients. CPI's health and safety summary points to amine catalysts, some with an "ammonia-like odor," that can be emitted "over the course of several hours to days." The blowing agent and the flame retardant were measured in the first hours after application in the studies CPI summarizes.

None of that is a reason to panic. It is the reason the house is empty during spraying and stays empty while the exhaust fans run.

How long normal spray foam smell lasts

There's no single number. It depends on the product, how much foam went in, the temperature, the humidity and above all the ventilation. The published guidance points the same direction:

Manufacturer instructions call for exhaust ventilation during spraying and for at least 24 hours after; one closed-cell guide sets a floor of 0.3 air changes per hour for that period. Another, for a high-lift HFO foam, calls for "a minimum of 24 hours following the application or until no objectionable odor remains." The 24 hours is a minimum, not a finish line.

Ventilation is what clears it

Odor is mostly a ventilation question. A good installer sets the job up so vapors leave the building instead of drifting through it. EPA's ventilation guidance and manufacturers' instructions cover the essentials:

• Plastic sheeting with taped seams to isolate the work area.
• Exhaust fans that hold the work area under negative pressure and blow outside, to a safe spot.
• The heating and cooling system shut down and its openings sealed, restarted only after the foam has cured and the area has been ventilated and cleaned.
• Absorbent items removed or covered. One manufacturer warns that odor from an unventilated application "can be absorbed in adjacent materials such as fibrous insulation, wood framing and household or stored items."
• Ventilation continued for at least 24 hours after spraying.

Once you're back home, ordinary ventilation clears the rest: bath and kitchen exhaust fans, open windows when the weather allows, and a mechanical ventilation system if the house has one.

A tighter house also holds smells longer. EPA notes that spray foam can "significantly decrease air exchanges," so emissions from foam, paint, new flooring or furniture build up more than they did in a leaky house. Plan for fresh air, especially after a whole-house job.

When the smell signals a problem

A smell that is still strong after the ventilation period, or that stops fading, deserves a look. Trade consultant Mason Knowles, writing in the Journal of Light Construction, says odors that last more than a week may indicate a problem. The usual suspects:

• Off-ratio foam. If the A and B sides weren't mixed 1:1, the excess doesn't react. CPI says off-ratio foam "will not cure properly and unreacted chemicals may be emitted," and resin-rich foam in particular is more likely to carry a high odor. It usually shows: discolored, chalky, soft, tacky or shrinking foam. See off-ratio spray foam.
• Passes sprayed too thick. Each foam has a maximum thickness per pass because the reaction makes heat. One manufacturer's instructions warn that exceeding it can produce "offensive odors that may not dissipate with time."
• Odor held by nearby materials. Even when the foam is fine, insulation, framing or stored belongings in a poorly ventilated space can hold the smell.
• Something else. New finishes, a damp crawlspace or a dried-out drain trap can get blamed on the foam.

The National Institute of Standards and Technology tested closed-cell foam taken from a home whose occupants had complained. It found more chemical compounds, generally at higher levels, than in research reference foams, and the authors wrote that the foam "may have been misapplied." It was one sample, but it lines up with industry guidance: well-made foam settles down, and badly made foam may not. For the visual signs that usually go with it, see how to spot bad spray foam.

What to do about a smell that won't go away

1. Note the details. Where it's strongest, when it's worse, and whether it's fading at all. Photograph the foam.
2. Call the installer. Ask for the product name, lot numbers, spray conditions and how the job was ventilated. CPI's homeowner FAQ advises contacting the contractor first to confirm proper installation and ventilation.
3. Call the manufacturer's technical service with the product and lot numbers.
4. Consider an indoor air quality consultant. CPSC staff suggest one when the source isn't clear, and EPA notes that indoor air sampling is one way to confirm the foam has fully cured.
5. Look after people first. If anyone has breathing problems or other symptoms, EPA and CPSC staff guidance is to seek medical attention. CPSC also takes reports at SaferProducts.gov.
6. If it isn't resolved, CPSC staff and CPI point to your state or local consumer protection office or contractor licensing board.

What not to do: cut, sand or heat the foam to find the smell. EPA warns that heat-generating work on foam can release isocyanates and amines.

Want a number for your own project? Price My Project or call (814) 208-3478.