If you are researching insulation upgrades for your Massachusetts home, you have likely encountered the question: is spray foam insulation a fire hazard? It is a valid concern. Between news reports of insurance companies flagging homes and the technical jargon thrown around by contractors, the topic of fire safety can feel overwhelming.
The short answer is that spray foam, like the wood framing holding up your house, is a combustible material. If exposed directly to a continuous flame, it will burn. However, when installed correctly according to the Massachusetts building code, it is entirely safe.
The danger does not come from the foam itself. The danger comes from “blow-and-go” contractors who skip the mandatory fire protection steps to offer you a cheaper quote. At Thermal Core Insulation, we believe in Code-First Insulation. Here is the building science behind spray foam fire safety, what the code requires, and how to protect your home.
Combustibility of Spray Foam
All foam plastic insulation, whether open-cell or closed-cell, is derived from petroleum. Because it is an organic material, it is inherently flammable.
To mitigate this risk, reputable manufacturers treat spray polyurethane foam (SPF) with chemical flame retardants during production. These retardants are designed to interfere with the combustion process, making the foam harder to ignite and slowing the spread of flames across its surface.
If you hold a lighter to high-quality, flame-retardant spray foam, it will char and may briefly catch fire. But if you pull the flame away, the foam will typically self-extinguish. The real hazard occurs during a sustained house fire. Under continuous, intense heat, the foam will eventually ignite, contributing to the fire and releasing smoke.
This is why the conversation around spray foam safety is never just about the foam itself, it is always about the assembly.
Open-Cell vs. Closed-Cell Fire Resistance
Homeowners often ask if one type of foam is safer than the other. The reality is that neither open-cell nor closed-cell foam is fireproof.
- Open-Cell Foam: Because it is lighter and less dense, open-cell foam tends to char and shrink away from a heat source, which can slow the burning process.
- Closed-Cell Foam: This denser, rigid foam maintains its shape longer under heat. However, because it contains more plastic material per square foot, there is more fuel available if it does ignite.
Both types require the same fire protection measures under the building code.
Understanding the ASTM E84 Fire Rating
When reviewing an insulation quote, you might see the contractor proudly state that their foam has a “Class A” or “Class 1” fire rating. While this sounds impressive, it is important to understand what it actually means.
Building materials are tested for their surface burning characteristics using a standardized test called ASTM E84. This test measures two specific metrics:
- Flame Spread Index (FSI): How fast flames travel across the surface of the material.
- Smoke-Developed Index (SDI): How much smoke the material produces as it burns.
To achieve a Class A rating, a material must have an FSI of 0–25 and an SDI under 450. Most high-quality spray foam products achieve this Class A rating.
However, a Class A rating does not mean the foam is fireproof, and it does not mean the foam can be left exposed. Even Class A spray foam must be covered by a thermal barrier to meet residential building codes.
The 15-Minute Rule: What is a Thermal Barrier?
Because spray foam is combustible, the Massachusetts Board of Building Regulations and Standards (BBRS) strictly regulates how it can be used. Under Massachusetts 780 CMR (which adopts the International Residential Code), spray foam cannot be left exposed in living spaces.
It must be separated from the home’s interior by a prescriptive thermal barrier.
The job of a thermal barrier is to delay a fire from reaching the combustible foam for a specific period of time, specifically, 15 minutes. This 15-minute window is a standard set by fire safety experts to give occupants enough time to evacuate the home before the insulation becomes involved in the fire.
Approved Thermal Barriers
The most common and universally accepted thermal barrier is 1/2-inch drywall. If you are spraying foam into the wall cavities of a living room or a finished basement, the drywall you install over the studs serves as the thermal barrier.
But what if you are insulating an area where installing drywall is impractical or too expensive, such as an unfinished basement ceiling, an attic roof deck, or a crawl space?
This is where many contractors cut corners. Instead of applying a barrier, they simply leave the foam exposed, leaving the homeowner with a massive fire hazard and a building code violation.
The Dual-Defense Intumescent Shield
If you cannot install drywall over your spray foam, the code allows for alternative thermal barriers, provided they have been rigorously tested and approved. The most effective solution is an intumescent coating.
An intumescent coating is a specialized, water-based fire-retardant paint that is sprayed directly over the cured foam. Under normal conditions, it looks like a thick layer of paint. But when exposed to the extreme heat of a fire, a chemical reaction occurs.
The coating swells to many times its original thickness, creating a dense, insulating “char” layer. This char layer acts as a physical shield, protecting the foam underneath from the flames and heat, fulfilling the 15-minute thermal barrier requirement.
At Thermal Core Insulation, we use industry-leading intumescent coatings like DC315 to create our proprietary Thermalcore Fire-Safe Envelope. This ensures that even in unfinished spaces, your home is fully protected and strictly compliant with Massachusetts fire codes. This is particularly critical for fire-rated insulation in MA multi-family buildings, where life safety requirements are even more stringent.
Will Spray Foam Void My Homeowners Insurance?
Recently, there has been a surge of anxiety among homeowners regarding spray foam and insurance coverage. This fear largely stems from a highly publicized mortgage crisis in the UK, where lenders refused to finance homes with spray foam due to improper installations that caused roof rot and fire hazards.
In Massachusetts, your homeowners insurance will not be voided simply because you have spray foam insulation. However, an insurance inspector will flag your home if they discover exposed spray foam that violates the building code, just as they would flag an unpermitted basement waterproofing job that damages the foundation.
If an inspector finds exposed foam in your attic or basement without a thermal barrier, your insurance carrier may threaten to cancel your policy or refuse to pay out a claim in the event of a fire.
The solution is simple: hire a contractor who practices Code-First Insulation. When your spray foam is properly covered by drywall or an intumescent coating, it is fully code-compliant, safe, and unproblematic for insurance carriers.
Don’t Let a Cheap Quote Put Your Home at Risk
When comparing quotes for spray foam insulation services, you will often find a wide variance in price. In almost every case, the lowest bidder is able to offer a low price because they are skipping the thermal barrier.
They will spray the foam, pack up their trucks, and leave you with a highly combustible basement or attic that violates Massachusetts law. If you ever try to sell your home, a home inspector will flag it. If you ever have a fire, the consequences could be devastating.
Spray foam is an incredible product. It provides unmatched thermal resistance, acts as a perfect air sealing system, and drastically lowers your energy bills. But it must be respected as a building material.
If a contractor tells you that their foam “doesn’t need a thermal barrier because it has a Class A fire rating,” they are either dangerously uneducated or intentionally misleading you.
Do it once, do it right, and do it safely. Contact Thermal Core Insulation today to learn more about the Thermalcore Fire-Safe Envelope and how we protect Massachusetts homes.
