Spray foam has become one of the top insulation choices for new construction and for retrofit in existing properties. It is a high-performance, high-profile product and has a market-leading R-value.

As with all home upgrades it is advisable to do as much research as possible. Investigate what materials to use, and what to avoid. When hiring a contractor, ensure they have a solid track record; experience counts for a lot. 

While there have been many successful installations of spray foam insulation, you might have noticed several stories reported in the media of unpleasant, and persistent lingering odors following a retrofit.

Here’s everything you need to know about what to do when a spray foam smells.

Is It OK for Spray Foam Insulation to Smell?

Spray foam insulation is a chemical process with two main base products mixed at the applicator gun during installation. The person carrying out the work is advised to wear full personal protective equipment (PPE) including a filter mask.

When the spray foam is applied directly to a surface an exothermic reaction begins, creating heat as the foam expands. As with some paint products, odors from volatile organic compounds (VOCs) are released as part of the normal curing process of spray foam. 

A contractor will usually require the house, in a retrofit scenario, to be vacated for at least 24 hours during the spray foam installation to prevent any exposure to the chemicals released during the installation. 

Likewise in a new build, the spray foam contractor will demand exclusive access to the installation area, requiring other trades to vacate.

Case #1. Spray Foam Smells Right After the Installation

It is normal for there to be a distinct smell directly following the installation of spray foam insulation. It is usual practice for the installation site to be vented to the outside for the duration of the works.

Spray foam usually contains Isocyanates, which are harmful if ingested, hence the recommendation by installers that the building to be insulated be vacated for a minimum of 24 hours. They are found in paint, in polymers used in the automotive industry and many household items such as carpets and upholstery.

In most installations the spray foam should have completed the curing process within 72 hours. Should a smell persist within the living area of your home then it may be that faulty ductwork running through the treated section of the building could be drawing in residual off-gassing smells.

In a loft installation check that the attic space is properly vented. 

In a crawl space, spray foam is a popular product when that part of the building is encapsulated. If the smell persists then continue to vent the space, perhaps by using a manual override setting on any fan installation.

Should the smell not diminish over time, or you feel it is too obtrusive, or perhaps you feel you might be having a physical reaction then contact the installer.

Case #2. Spray Foam Smells on a Hot Day

It is usual to insulate the floor of an attic space in order to maintain ventilation to the roof structure, keeping the space dry. In the summer months it can get extremely hot under the shingles.

When this happens, the hydrocarbons present in old tar paper can be revitalized by the heat and begin to smell. Preservative chemicals used to treat the roof beams can be affected in the same way.

Similarly, consistent high temperatures could also possibly provoke some limited further off-gassing of spray foam. Combine this with other sources of these other common home chemical compounds and the resulting odor, while unpleasant, is not unexpected during a heatwave and is usually limited to the attic space.

It all comes down to proper venting of the attic space to create negative pressure so that unpleasant odors do not impair the air quality in the living areas of the house. On a hot day the insulation in your attic should be playing its part, ensuring that your home remains as cool and comfortable as possible.

If you have services running through the insulated space, ensure that any penetrations are properly sealed and that vents are maintained.

Case #3. Spray Foam Smells All the Time

There has been anecdotal evidence that people have been chemically ‘sensitized’ following a spray foam installation, but nothing conclusive. People point to the fact that installers wear full PPE when fitting spray foam, but that is simply sensible practice.

When an installer fits fiberglass or rockwool in an enclosed space they are recommended to wear the exact same PPE.

Problems With the Method of Installation of Spray Foam

  • The fear factor arises at the point of installation when the chemicals are mixed at the nozzle to produce the spray foam. The mechanics of the method are straightforward but are not absolutely perfect.
  • The spray foam has to be spread uniformly, and thinly across the area to be insulated. If the installer is too slow, then the foam layer can become too thick, potentially slowing down the chemical reaction and delaying curing time.
  • When a second coat is sprayed over this area, as is standard practice, then it may be possible to trap this earlier, thicker, layer below. It is thought that this might cause a further delay to the eventual, final off-gassing of the product.

What Can Happen Next?

The good news is that by taking core samples, it is possible to identify where any late off-gassing might be happening. The remedy is simply to identify the poorly installed patches and have them removed and replaced.

But removal is difficult and depending on where the offending installation is situated you may find your contractor will have to remove ceilings or drywall for access.

Off-Gassing Mitigation in Lofts

Some contractors fitting spray foam in lofts will fit a fan to assist venting as standard, and always aim to maintain negative air pressure in an attic, just in case. This may be helpful in certain circumstances.

Crawl Space Spray Foam Off-Gassing

It is unlikely that bad odors from the spray foam in your crawl space will become an issue. If the crawl space has been properly constructed, then smells should be vented directly to the outside atmosphere.

If there are smells rising through the floor into the living space, then it would be wise to check the ductwork is properly sealed and that all service entryways are protected and closed up.

Wall Space Spray Foam Off-Gassing

If the attic and the crawl space have both been ruled out as offenders, and the smell is persisting in the home it’s time to check the wall spaces. In new builds and extensions spray foam is often used between the timber wall studs to provide insulation and an effective moisture barrier.

With a professional installation done properly, there is rarely a problem. However, because these areas are closed up with drywall, they are impossible to vent the same way as other areas of the property.

If the spray foam is identified as causing the smell, and it cannot be cured by other means, i.e. by applying heat etc, then it will have to be removed. 

Case #4. What If It’s Not the Spray Foam?

Managing Expectations

An installer in Georgia has said that if a client was overly concerned prior to installation that they would suffer from unpleasant and sometimes invasive smells from spray foam, then he was certain that the client would not be disappointed.

In that case, the installer would recommend an alternative, inert product for their attic insulation. The advice is clear; if in doubt, use a different product.

On hot days some clients had reported a smell in the hallway directly below the loft access. A loft access sealing bag is an inexpensive way of reducing leaks from the attic space. Problem solved.

Wildlife Issues

Some clients have reported a ‘fishy’ smell, while others reported an odor similar to ammonia. Birds and small mammals excrete urea, which can in some cases give off a similar chemical smell.

The recommendation is to check that vents and ducts are secure and properly maintained and that any entryways for birds, rats, bats, or lizards are in order. In Northern states the American Marten prefers clean, dry lofts, but will create very unpleasant smells, toileting next to where it nests.

Survey Issues

If the treated area was not properly inspected prior to installation, then it may be that mold or moisture might have been trapped behind the spray foam. Ensure the surface to be insulated is completely dry before work begins.

As spray foam is such an effective insulator, and moisture barrier, the resulting smell could be a warning sign that your building has bigger problems. Check the ceilings by external walls for any color changes. As moisture can no longer evaporate into the loft space, it now has to find another way out.

Retained Odors

It may be that the spray foam insulation was part of a retrofit installation, replacing an older fiberglass product. Fiberglass can be very absorbent. Should there be any left in an attic or crawl space during the works, then it could be a source of the offending smell.

Ensure that any debris from old insulation is removed prior to installing spray foam. Old batts can harbor mold and mildew, and you don’t want to trap it with spray foam.

Old ductwork is sometimes wrapped in foil-backed rockwool and could also retain some of the off-gassing odor over time.


Evan has decades of experience as a project manager for large-scale commercial renovation home-building projects throughout the US. Currently, Evan runs a successful construction management company in Virginia.

Write A Comment