Spray foam insulation is safe to live with when it is installed correctly and nobody but the crew is in the house while it goes in and cures. The hazard is the installation. The EPA says isocyanates, the key ingredient, and other spray foam chemicals in vapors, aerosols and dust during and for a period after installation can cause asthma, sensitization, lung damage and skin and eye irritation. That is why installers wear respirators and everyone else leaves.
Cured foam is a different material: the EPA says foam that is correctly applied and allowed to fully cure is typically considered relatively inert. Two honest caveats come with that. The same agency says the potential for off-gassing is not fully understood, and that foam mixed or sprayed wrong can leave unreacted chemicals that may off-gas over time. Foam is also combustible, so the building code decides what covers it.
So the real question is whether this product, this crew and this plan will get it right in your house.
What makes spray foam hazardous while it goes in
Spray foam is made on site from two liquids. The American Chemistry Council’s Center for the Polyurethanes Industry, an industry trade group, describes the A side as methylene diphenyl diisocyanate (MDI) and polymeric MDI, and the B side as polyols blended with catalysts, blowing agent, flame retardant and surfactant. They meet at the spray gun and react into foam.
- Isocyanates. OSHA names occupational asthma and other lung problems, and irritation of the eyes, nose, throat and skin, as the main effects of hazardous exposure. The EPA says breathing exposures during spray foam insulation work will typically exceed OSHA’s occupational limits.
- Sensitization. Some people become allergic to isocyanates. The EPA says that once someone is sensitized, even low concentrations can trigger a severe asthma attack, symptoms can be delayed up to several hours, and there is no recognized safe level of exposure.
- The B side. The EPA notes amine catalysts may be sensitizers and irritants that can blur vision.
- Drift and dust. Vapors and aerosols can move through a building that isn’t isolated and ventilated, according to the EPA, and trimming foam before it has cured can make dust that may carry unreacted isocyanates.
The EPA’s ventilation guidance says manufacturers’ safety data sheets generally call for full face-piece or hooded supplied-air respirators. If the crew needs that, the family, the pets and the other trades belong somewhere else.
What cured spray foam is
The EPA warns that foam can look hard, or “tack-free,” within seconds to minutes while it is still curing and still holds unreacted chemicals. How long curing takes depends on the product, the applicator’s technique, foam thickness, temperature and humidity.
The Spray Polyurethane Foam Alliance, a spray foam trade association, says several products have been independently tested for volatile organic compound emissions, under GREENGUARD, CAN/ULC S774 and California’s Section 01350 method, with no significant levels measured after the prescribed cure periods. The EPA says more research is needed on off-gassing and on the foam’s long-term stability. Those industry results describe a tested product installed to its instructions, not an off-ratio job.
- Don’t heat cured foam. The EPA says drilling, welding, soldering, grinding, sawing or sanding on or near it can release isocyanates, amines, carbon monoxide and hydrogen cyanide, and that plumbers and electricians should not heat or grind it. Tell anyone who works near it later.
- Mind the air. The EPA points out that insulation seals a house and cuts air exchange, so emissions from any source, fuel-burning appliances included, can build up. Its contractor checklist says combustion appliance areas may need added air, a question for an HVAC professional. See air sealing.
How long to stay out of the house after spray foam
Everyone who isn’t on the spray crew leaves before spraying starts, pets included. The EPA says re-entry waits until the foam has finished curing and the building has been adequately ventilated and thoroughly cleaned. How long that takes is the manufacturer’s number, not a guess:
- Professional high-pressure foam: the EPA reports that some manufacturers recommend 24 hours before residents return, and that the time may vary. The Chemistry Council group says many suggest 24 hours with the recommended ventilation, counted from when spraying is completed, and calls that conservative, based on field studies, modeling and chamber tests of a generic product.
- Low-pressure two-component kits: for an interior application, the Chemistry Council group says some manufacturers recommend one hour.
- One-component cans: the EPA says some manufacturers estimate 8 to 24 hours to cure.
The time moves with the formulation, the amount of foam for the size of the space, temperature, humidity and ventilation, so get the number for your product and job in writing before work starts. The EPA also asks homeowners to consider children, who crawl and sit on floors where dust and residue can settle; children with asthma are an especially vulnerable population.
What a careful crew does on spray day
- Heating and cooling serving the work area is shut down and its openings sealed. The EPA says to restart it only after the foam has cured and the area has been ventilated and cleaned.
- Pilot lights go out. The Chemistry Council group lists gas stoves, dryers, furnaces and water heaters in the spray area, the rooms next to it and behind neighboring walls.
- The work area is closed off with plastic sheeting kept under negative pressure, so leaks pull air in, and exhausted outdoors away from people and air intakes. Fans aimed at the work without a planned airflow, the EPA warns, only stir the fumes around.
- Ventilation continues until the foam has cured and the vapors are gone. Then dust and trimmings are cleared by workers in protective gear, and the chemical drums leave with the crew.
Spray foam smell and off-gassing
Some products smell for several days. The Spray Polyurethane Foam Alliance says that odor usually comes from unreacted amine catalysts and has been described as fishy, like cat urine or like fresh latex paint. The Alliance calls it a nuisance rather than a sign of chemical hazard and recommends extra ventilation for a few days.
A smell that lingers, or a different smell, is a warning. The Alliance says persistent or other odors, and foam that is discolored, sticky or crumbly, are symptoms of an improper install. The EPA lists what spoils the cure: temperature and humidity; the heating and cooling left running and vents left unsealed; and poor technique, meaning the A and B sides mixed or proportioned wrong (off-ratio foam) or foam sprayed too thick. That can leave unreacted chemicals that may off-gas over time and migrate to other surfaces. The EPA gives no timeline; it says standardized methods for measuring spray foam emissions are still needed.
What to do if spray foam still smells
- Health first. If anyone has breathing problems or other symptoms, the EPA says to seek immediate medical attention.
- Call the contractor to confirm installation, ventilation and cleanup were done properly, as the EPA and the Chemistry Council group both advise.
- Diagnose before tearing anything out. The EPA suggests the contractor and the manufacturer, or an independent indoor air quality consultant. Air testing by a certified laboratory using a validated method is one way to confirm the foam has cured.
- Escalate if it isn’t resolved, to your local or state consumer protection office or contractor licensing board, and report it to the Consumer Product Safety Commission at SaferProducts.gov, as the EPA suggests.
Don’t count on removal to fix an odor. The EPA warns that chemicals from a bad install may have migrated to other surfaces and be the source of the smell, so removal may not solve it and can create other problems.
Open cell vs closed cell: what differs for safety
Open cell (R-3.9 to R-4.2 per inch) and closed cell (R-6.9 to R-7.1 per inch) both start with isocyanates, and the EPA says the chemical components and related hazards are similar across spray foam products. Leaving the house applies to both. The differences:
- Blowing agent. The EPA’s product chart lists carbon dioxide or water for open cell. For closed cell, the Alliance says the industry has been moving from HFC to low global warming potential HFO blowing agents. The Chemistry Council group lists irregular heartbeat as a symptom of overexposure to certain blowing agents, an installer’s hazard.
- Heat. The Chemistry Council group says closed cell retains more of the reaction’s heat and stays hotter longer. The Alliance says closed cell sprayed thicker per pass than the manufacturer allows can shrink and lose R-value, and in extreme cases, at several times the limit, ignite itself. It also notes reports of higher peak temperatures in some HFO foams at maximum pass thickness.
- Re-occupancy and fire rules follow the product and the code, not the foam type. Both foams are combustible.
Be wary of foam sold as “non-toxic.” The EPA warns that some spray foam marketing doesn’t make clear the products contain hazardous chemicals, which hides the need for protective gear and ventilation. The straight answer: cured foam is considered relatively inert; the liquids that make it are not. Choosing between the two: open cell vs closed cell spray foam.
Mold, roof leaks and the mortgage question
The Alliance says spray foam is not a food source for mold, but dust collecting on it plus moisture can grow mold in a poorly designed or built assembly, as with any insulation. The bigger risk is water you can’t see. The Royal Institution of Chartered Surveyors, a UK-based professional body, notes that a roof leak behind some types of spray foam may go unnoticed and rot the timber. Fix roof leaks before foam goes on a roof deck.
The “spray foam mortgage problem” comes from that British guidance, which says foam sprayed under existing roofs can affect a surveyor’s opinion of value and tells owners to keep the contract, warranty, test certificates and photographs from before and after the work. It is written for UK homes and lenders, but keeping that paperwork is good practice anywhere.
Fire safety: thermal and ignition barriers
Spray foam burns. The Chemistry Council group says foams typically contain flame retardants and are designed to meet building and fire codes when installed properly, but cured foam burns in direct flame, and the EPA says spray foam fires can release isocyanates, hydrogen cyanide and other toxic chemicals. The International Residential Code covers the foam: Section R316 of the 2021 edition, which Connecticut uses, and R303 of the 2024 edition, adopted in New Jersey and New York.
- Flame spread. Foam up to 4 inches thick needs a flame spread index of 75 or less and a smoke-developed index of 450 or less (R316.3.1, R303.3.1).
- Living space, basements and garages: a thermal barrier. At least 1/2-inch gypsum wallboard, 23/32-inch wood structural panel, or a material that passes the NFPA 275 fire tests (R316.4, R303.4). Under a floor it goes on the underside wherever that faces the inside of the building, a basement ceiling included (R316.5.13, R303.5.13). No exception covers garage walls or ceilings, and the walls and ceilings between a garage and the house have their own gypsum board rules (Table R302.6). See basement insulation and garage insulation.
- Attics and crawl spaces entered only for repairs or maintenance: an ignition barrier can do instead, such as 1 1/2 inches of mineral fiber insulation, 1/4-inch wood structural panel, 3/8-inch gypsum board or 1/4-inch fiber-cement board, and in attics 1 1/2 inches of cellulose (R316.5.3 and R316.5.4; R303.5.3 and R303.5.4). Store things up there or finish the space, and it needs a thermal barrier. See attic insulation.
- Rim joists. Foam no more than 3 1/4 inches thick, 0.5 to 2.0 pounds per cubic foot, with a flame spread index of 25 or less and a smoke-developed index of 450 or less, can stay exposed (R316.5.11, R303.5.11).
- Tested assemblies. Foam approved on a large-scale fire test of its actual use can go without those barriers (R316.6, R303.6). Some foams are approved this way bare or under a sprayed intumescent coating; one manufacturer’s data sheet lists approved coatings, with conditions such as no storage in the space.
On the job, the Chemistry Council group says to keep high heat, flame and smoking away from the spraying, and afterward to keep welding, torch cutting and flame-producing heaters away from cured foam until an ignition barrier such as drywall covers it. The Department of Energy says active knob-and-tube wiring should be replaced before an insulation project begins; see insulation for older homes.
Who should take extra care
The EPA says people with a history of skin conditions, respiratory allergies, asthma, or prior isocyanate sensitization should carefully review product information before using spray foam and may want to consider alternatives. It notes that manufacturers’ safety data sheets restrict people with those histories from working with isocyanates.
If that describes anyone in your household, talk to their doctor before the job is scheduled. Bring the safety data sheets for both sides of the product and the manufacturer’s re-occupancy time, and ask whether that person should stay away longer or whether a different insulation makes more sense. That call belongs to the doctor, not the installer.
Questions to ask any spray foam installer
These come from the EPA’s contractor-client checklist and homeowner guidance, and the Chemistry Council group’s advice on what a contractor should explain. Ask them before you sign:
- What product, exactly? Manufacturer and product name, with the safety data sheets and product literature.
- How long do we stay out, counted from when, and will you put it in writing?
- How will you isolate and ventilate the work area during and after spraying, and where does the exhaust go?
- What will the crew wear? The EPA lists appropriate respirators and chemical-resistant gloves and clothing.
- What temperature, humidity and surface moisture does the product need? Ask how those, and the rig’s temperatures, pressures and A-to-B ratio, get checked on the day.
- How thick is each pass, and how long do you wait between passes?
- What happens to the heating system, the vents and the pilot lights?
- What covers the foam, under which code section, and who installs it?
- What does cleanup include before we come back?
- What training does the crew have, and are you licensed and insured? The EPA tells homeowners to confirm training, verify insurance and licenses, and check references.
- If the foam smells or cures badly, who diagnoses it, and who pays if it has to be cut out?
Ask us every one. Our spray crew is in-house and never subcontracted, so the company answering these questions is the one whose crew sprays your house.
DIY spray foam kits and cans
The EPA says two-component high-pressure foam is a professional system for trained applicators only. Low-pressure kits and one-component cans are sold to homeowners, but the EPA says the same precautions apply, do-it-yourselfers are often unaware of the breathing and skin hazards, and the products should not be used around children. The Chemistry Council group draws the line by size: cans for sealing gaps around windows, doors and small cracks; walls, attics and roofs for professionals. What professional work costs: spray foam insulation cost.
Can spray foam insulation be removed?
Yes, but it is slow, dusty, labor-intensive work, and we do it: we remove foam and other insulation and put new material back. The American Chemistry Council’s spray foam coalition publishes removal guidance for the contractors who do it:
- Why foam comes out: renovations that open the wall or roof, and foam damaged by fire, flood or mold.
- The hazard: cutting cured foam makes dust that can irritate skin, eyes and airways, so the guidance calls for containment under negative pressure, exhaust ventilation, a respirator, eye protection, gloves, coveralls and a HEPA vacuum.
- Open cell comes off fairly easily: cut from the sides of the framing with a serrated trowel or drywall saw, then scraped off the sheathing.
- Closed cell is rigid. Except for very small areas, it may take a reciprocating or circular saw and a spud bar. A very thin layer may stay bonded, and grinding or blasting it off typically takes a thin layer of the wood with it.
- What’s buried in it: wiring, plumbing and ducts, and under a roof deck, roofing nails. Circuits get shut off at the breaker first.
The EPA has said it knows of no standard accepted removal practice, and warns that heating or grinding foam can release toxic emissions. The British surveyors’ guidance calls spray foam not reversible, because removal can damage the structure. So remove foam only for a diagnosed reason, and only with the containment and ventilation that removal guidance calls for.
How spray foam compares with other insulation
With fiber insulation, the concern is dust when the material is installed or disturbed, not curing chemistry.
- Fiberglass and mineral wool. The Agency for Toxic Substances and Disease Registry says airborne fibers can irritate the eyes, nose, throat and lungs, and fibers on the skin can irritate it; the effects are reversible and disappear shortly after exposure stops. It reports that the International Agency for Research on Cancer found insulation glass wool, stone wool and slag wool not classifiable as to whether they cause cancer in humans. Its advice: don’t disturb the insulation, and wear protective clothing and respiratory and eye protection to install it.
- Cellulose. Recycled newsprint treated with borate, sometimes blended with ammonium sulfate, for fire and insect resistance, according to the Department of Energy, which also says to keep it away from chimneys and metal flues. The code requires loose-fill cellulose to meet Consumer Product Safety Commission standards (IRC Section R302.10.3). A NIOSH study of installers found total dust above OSHA’s limit in virtually all application work, less dust with moistened material, eye symptoms linked to the work, and little evidence of lower respiratory conditions; it recommended respirators.
- Vermiculite. Pebble-like old loose fill, usually gray-brown or silver-gold. The EPA says to assume it may contain asbestos, leave it undisturbed, and hire a professional asbestos contractor before any work that would disturb it.
How the materials perform: types of insulation.
Common questions about spray foam safety
Is spray foam insulation safe?
Once correctly applied foam has fully cured, the EPA says it is typically considered relatively inert. The hazard is during installation and curing, when isocyanates and other chemicals in vapor, aerosol and dust can cause asthma, sensitization and irritation. Stay out until the manufacturer’s re-occupancy time has passed and the space has been ventilated and cleaned, and cover the foam as the fire code requires.
How long after spray foam can you go back in the house?
For professional high-pressure foam, the EPA reports that some manufacturers recommend 24 hours, and the American Chemistry Council’s polyurethanes group says many suggest 24 hours with the recommended ventilation, counted from when spraying ends. Some low-pressure kits list one hour. The right number is the manufacturer’s for your product, in writing before the job.
Is spray foam toxic after it cures?
The EPA says correctly applied, fully cured foam is typically considered relatively inert, and also that off-gassing is not fully understood. Foam that was mixed wrong may off-gas unreacted chemicals over time, and cured foam can give off toxic gases if it burns or is heated by welding, grinding or sanding.
Why does my spray foam insulation smell?
The Spray Polyurethane Foam Alliance says some foams smell for several days from unreacted amine catalysts, and extra ventilation helps. A smell that persists, or foam that is sticky, discolored or crumbly, points to an improper install. Call the contractor, and if anyone has breathing problems, get medical attention.
Is closed cell spray foam safer than open cell?
Not in a way that changes what you do. Both are made with isocyanates, both require an empty house while they go in, and both are combustible under the same code barriers. Closed cell holds more heat as it reacts, so pass thickness matters more. Re-occupancy is set by the product, not the foam type.
Can I stay in the house while spray foam is installed?
No, not even in another room. The EPA says occupants and other trades should leave during installation, because vapors and aerosols can move through a building, and not return until the foam has cured and the house has been ventilated and cleaned. Make plans for pets too.
Is spray foam insulation flammable?
Yes. It typically contains flame retardants, but cured foam burns in direct flame. The International Residential Code requires a thermal barrier such as 1/2-inch drywall between foam and the inside of the house (R316.4 in 2021, R303.4 in 2024), with ignition-barrier rules for attics and crawl spaces entered only for repairs or maintenance.
Is spray foam safe for someone with asthma?
Ask their doctor before scheduling. The EPA says people with asthma, respiratory allergies, skin conditions or prior isocyanate sensitization should carefully review product information and may want to consider alternatives, and it calls children with asthma especially vulnerable. Bring the safety data sheets and re-occupancy time to that appointment.
Can spray foam insulation be removed?
Yes. Open cell cuts and scrapes off fairly easily; closed cell is rigid and may take saws and a spud bar, sometimes leaving a thin bonded layer. Industry removal guidance calls for containment, exhaust ventilation and respirators because of the dust, and the EPA warns removal may not fix an odor.
Is blown-in insulation safer than spray foam?
Different, not simply safer. Fiberglass and mineral wool fibers can irritate skin, eyes and airways, effects the ATSDR calls reversible, and cellulose installation is dusty enough that NIOSH recommended respirators for installers. There is no curing to wait out, but dust matters whenever the material is installed or disturbed.
Spray foam from The Home Insulators
Before we quote foam, we look at where it would go and how the space is used, because that decides the barrier the code requires and whether foam is the right material at all. If someone at home has asthma or a chemical sensitivity, tell us early; we also install blown-in cellulose and fiberglass, and fiberglass and mineral wool batts. Most of our projects run between $3,500 and $12,500. The energy audit is free.
Call 914-554-2289 or use the contact form, 8am–8pm, seven days. The Home Insulators is family-owned, based in New Rochelle, NY since 2015, with a 100-plus-person in-house crew that never subcontracts. We work across all of New Jersey and Connecticut, New York’s Hudson Valley and Long Island; see our service area.