What are the disadvantages of spray foam insulation?

Spray foam insulation has become an increasingly popular choice for insulating homes and buildings in recent years. This type of insulation offers many advantages over traditional fiberglass and cellulose options, such as better air sealing, higher R-values per inch, and resistance to moisture. However, spray foam is not without its downsides. Here we will explore some of the key disadvantages of spray foam insulation that homeowners should be aware of.

Higher Upfront Cost

One of the biggest drawbacks associated with spray foam insulation is its high initial cost compared to other types of insulation. Installing spray foam typically costs $1.50-$2.50 per square foot, making it one of the more expensive insulation options. Fiberglass batts, on the other hand, cost around $0.50 per square foot. The large price difference is due to the materials and specialized equipment required to properly install spray foam.

While the initial investment is high, spray foam can provide better long-term value through energy savings. The superior air sealing and higher R-value per inch can lead to lower heating and cooling costs that offset the higher upfront cost over time. However, the return on investment depends on factors like climate, utility rates, and how much insulation is needed.

Potential Health and Environmental Risks

Certain types of spray foam insulation utilize potentially hazardous materials during installation that can present health risks if proper precautions are not followed. For example, the isocyanate compounds found in some spray foam products have been linked to asthma, skin irritation, and other issues when inhaled or exposed to the skin. The vapors released during application require workers to wear proper protective gear to minimize risks.

There are also environmental concerns related to some spray foam ingredients that deplete the ozone layer, potentially increase smog, or cause air quality issues. Most spray foams today no longer contain these problematic blowing agents, but it is still important to verify the specific foam you choose does not utilize them.

Can Absorb Moisture Over Time

While closed-cell spray foam is considered resistant to moisture, it is not entirely moisture proof. Over an extended period, spray foam insulation can absorb small amounts of water from vapor diffusion through the foam, plumbing leaks, or exterior water intrusion. Too much moisture buildup could compromise the insulation value of the foam or lead to issues with mold or mildew growth if a leak occurs.

Using spray foam to insulate areas at higher risk of moisture exposure, such as below-grade foundation walls or the perimeter of tubs/showers, requires extra care to prevent problems. Combining the foam with a vapor retarder, using closed-cell foam formulated for high humidity environments, and proper installation are key to minimizing moisture-related issues.

Requires Specialized Equipment and Training

Installing spray foam insulation is a more complex process than rolling out fiberglass batts or blowing cellulose in an attic. It requires specialized spray rigs to correctly mix and disperse the foam components, as well as formal training to apply the foam properly. The curing foam expands rapidly and will stick to anything, making precision and skilled technique important.

For these reasons, spray foam is almost always installed by professional applicators with the right tools and knowledge, rather than being a do-it-yourself project. Finding a qualified professional installer is important for getting the advertised results from the foam insulation.

Can Be Damaged During Construction

Unlike fiberglass or cellulose, spray foam insulation is permanently bonded to the surfaces it is applied to. This advantage can also be a disadvantage during construction or renovations. If the insulation gets damaged, scraped, cut into, or punctured, it cannot simply be refluffed or patched like other insulations. The affected section would need to be removed and replaced, which can be costly and time consuming.

Any construction or modification to an area with spray foam, such as running new wires or plumbing, needs to be done carefully to avoid harming the insulation. Damaged areas also become compromised on air sealing and moisture protection until fixed. Planning ahead helps avoid unnecessary insulation repairs down the road.

Requires Careful Sealing for Best Performance

To achieve the rated R-value and proper air sealing, spray foam insulation must make full contact with the surfaces it is applied to. Any gaps, cracks, or compressed areas will compromise insulation performance. Spray foam bonds well on its own, but care must still be taken to correctly seal any voids or joints.

Particular attention must be paid to sealing penetrations made for electrical, plumbing, vents, and other openings that intersect the foam insulation. Using spray foam accessories like backer rods or covers, as well as caulk and sealants, ensures critical junctions do not leak air or heat.

Can Present Fire Risks if Exposed

Spray foam insulation is combustible and will burn if exposed to an ignition source and oxygen. Building codes require covering spray foam with a thermal barrier material such as drywall to provide fire protection. Exposed foam in attics or other spaces can pose a fire risk if ignition were to occur.

Additionally, spray foams with a high flammability rating cannot be left exposed in interior conditioned spaces. Using an ignition barrier coating or covering the foam is necessary in these cases according to code. Following fire safety codes minimizes any risks from exposed spray foam.

Can Be Messy During Application

The liquid foam precursors tend to spray, splatter, and overflow during the application process before expanding and hardening. The monomers will stick to surfaces where overspray lands and cure into hardened foam residue. The spraying also generates a noticeable odor during and after installation.

Protecting floors, walls, and other areas from overspray and cleaning up residue after installation adds time and labor to the job. Some messiness is inherent when spraying foam insulation, so expectations should be set accordingly. Proper masking and prep helps minimize cleanup.

Can Present Future Removal Difficulties

Removing spray foam insulation once applied is extremely difficult, if not impossible, because it adheres tightly to surfaces. This permanence is an advantage for the long-term performance of the insulation. However, it can make modifications, repairs, or replacements to the foam itself or anything underneath it challenging.

Areas like wall cavities may need to be abandoned and re-built rather than attempting to remove old spray foam during renovations. There are some accounts of using solvents or mechanical means to remove foam, but often the effort outweighs starting fresh. Design plans should assume existing spray foam will remain in place.

Dense-Pack Formula Can Compress Over Time

Certain spray foam products utilize dense-pack formulas optimized to cram into confined cavities. The high-density foam does resist settling over time. However, there is still a potential for slight compression which would lower the R-value and air sealing ability compared to when first installed.

The compression is more pronounced in high load-bearing areas, such as foundations and structural framing. Using a formula rated for these specific applications minimizes density loss. Regular inspections also help detect any settling issues.

Closed-Cell Foam Acts as a Vapor Barrier

Closed-cell spray foam forms a robust vapor barrier thanks to its low permeability and seamless application. This helps prevent condensation issues within wall cavities or other insulated areas by blocking moisture diffusion.

However, too much closed-cell foam insulation can potentially trap unwanted moisture already inside the structure. A complete thermal enclosure without venting may result in moisture accumulation and related problems in some climates. Integrating the insulation with other vapor control methods is important.

Difficult to Verify Installed Thickness

Unlike fiberglass or cellulose, it is not easy to measure the thickness of cured spray foam insulation inside enclosed cavities. Yet the final thickness directly impacts the R-value and is used to calculate the number of bags needed. An applicator may incorrectly estimate how much foam to install in a given space.

There are thermal imaging cameras capable of detecting differences in foam thickness behind surfaces. Otherwise, taking exploratory core samples is the main way to physically verify thickness once cured. A trustworthy applicator dedicated to achieving the specified R-value is optimal.

Higher Lifecycle Embodied Carbon

The chemical components give spray foam insulation a higher embodied carbon footprint from raw material extraction through manufacturing compared to fiberglass or cellulose. Transportation emissions are also higher due to the liquid chemicals being heavier than rolls of batt insulation.

One analysis found spray foam insulation can have 2-5 times the embodied carbon of traditional insulation per square foot. This means more total carbon is invested in the insulation itself. The improved energy efficiency may still yield a net carbon benefit over time through energy savings at the building level.

Can Be Abused as a Quick Fix

The superior air sealing ability of spray foam could tempt some builders to use it as a shortcut to patch envelope leaks rather than addressing underlying deficiencies. However, the best practice is still to seal major leaks and penetrations thoroughly before insulating.

While spray foam will seal leaks as it expands into gaps, simply spraying over too many holes and cracks can impact insulation adhesion and performance. A disciplined approach that uses spray foam as one component of comprehensive air sealing is ideal.

Applications are Sensitive to Temperature

Spray foam insulation needs to be applied within the proper temperature range specified by the manufacturer, usually 40–80°F. Colder temperatures can greatly slow down or stop the chemical curing reaction, while too much heat speeds expansion and negatively impacts final density and adhesion.

Temperature regulation and monitoring are necessary during installation, which may require tenting or heating/cooling an area at added cost. Once cured, the foam is not sensitive to temperature extremes. Only the application window requires strict climate control.

Limited Thermal Barrier Options

Building codes restrict the types of materials that can be used as an ignition barrier over spray foam insulation. Common options like unfaced fiberglass batts are not considered thermal barriers, leaving only gypsum board, cement board, or other specialty materials. This can add material costs compared to other insulations.

Additionally, existing surfaces usually need to be retrofitted with new thermal barrier layers when adding spray foam to comply with code. The limited options and potential retrofitting should factor into installation planning and budgets when using spray foam.

Risk of Future Formula Changes

The specific chemical formulation used to create spray foam insulation can change over time as manufacturers tweak properties, switch suppliers, or alter ingredients to meet regulations. These changes may occur without notice or after the fact.

Formula modifications could lead to slight differences in the final performance or specifications compared to the original foam installed years earlier. Major changes are uncommon, but it is a potential variable to keep in mind with any spray foam installation.

Odor May Linger After Installation

Newly installed spray foam insulation can emit a distinct odor for several weeks as leftover volatiles escape during the final curing process. The smell may be noticeable indoors or permeate belongings stored in an attic space undergoing spray foam application.

Off-gassing odors do eventually dissipate over time once curing is complete. Keeping windows open during and after installation, running ventilation fans, and removing sensitive items helps manage any bothersome smells from the spray foam application.

May Require Multiple Layers

In cavities deeper than about 2 inches, spray foam insulation often needs to be applied in multiple passes or layers. The expanding foam will gradually cool and dissipate heat after each pass, allowing additional layers to build up to the desired overall thickness.

Applying too much foam at once without allowing it to cool down can cause irregular curing and lower-density foam. Multiple layers may be unavoidable based on the space, taking extra time and using more material compared to filling a cavity in one pass.

Can Cause High-Bill Complaints if Improperly Installed

Complaints of higher than expected energy bills and uncomfortable hot/cold spots sometimes stem from poor spray foam insulation installation. If the foam is not properly measured and mixed, does not fully fill cavities, or is installed too thin, the performance will suffer.

These issues underscore the importance of a skilled installer using the right equipment and techniques monitored with thermal imaging. Homeowners should only hire reputable professionals for spray foam projects to minimize risks of an improper application.

Fossil-Fuel Derived Chemicals

Most closed-cell spray foam products use petroleum-derived ingredients as raw materials. As the world moves toward decarbonization, demand may gradually shift toward more biosourced or recycled content in spray foam chemistry. Currently, fossil-fuel-based chemicals still dominate most formulations.

Sourcing spray foam from a manufacturer investing in sustainable materials or disclosing its environmental impacts allows homeowners to make an informed choice aligned with their values. But commercially available options remain predominantly petroleum-based as of now.


While spray foam insulation offers meaningful benefits compared to other insulation types, it also comes with downsides to consider. The high upfront cost, health risks during installation, sensitivity to proper technique, and difficult removal make spray foam less ideal for some situations and budgets.

However, for homeowners who can accommodate the drawbacks and leverage the strengths of spray foam, it can provide superior thermal and air sealing performance when properly installed. Weighing these pros and cons helps determine if spray foam is the right insulation choice for a given home or building project.

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