When installed correctly, open-cell spray foam is a safe and effective insulation material. By itself, it is a combustible plastic, but it achieves its required level of fire safety when covered by an approved thermal or ignition barrier. The primary fire performance metric to look for is the ASTM E84 test rating, which measures flame spread and smoke development. A Class A rating is the best possible result, indicating the lowest flame spread and smoke generation.
Understanding these ratings and the associated building code requirements is essential for a safe, compliant, and effective insulation project. This guide breaks down the fire safety classifications for open-cell spray foam, explains the role of protective barriers, and details what you need to check before installation. The information here is based on extensive field experience installing spray foam insulation and ensuring every project meets or exceeds local fire and building codes.
The most important fire test for interior finishes, including spray foam insulation, is ASTM E84. This standard test method evaluates the surface burning characteristics of a material. A report from the U.S. Department of Agriculture explains that this test produces two critical numbers: the Flame Spread Index (FSI) and the Smoke Developed Index (SDI).
Building codes use these two indices to classify materials into three categories: Class A, Class B, and Class C.
| Class | Flame Spread Index (FSI) | Smoke Developed Index (SDI) | Common Application |
|---|---|---|---|
| A | 0 – 25 | 0 – 450 | Walls, Ceilings |
| B | 26 – 75 | 0 – 450 | Corridors |
| C | 76 – 200 | 0 – 450 | Floors |
Most building codes require spray polyurethane foam to achieve a Class A rating. You can find a product’s specific ASTM E84 rating on its technical data sheet (TDS).
Because spray foam is combustible, building codes do not permit it to be left exposed in most residential and commercial spaces. It must be separated from living areas by an approved barrier. The type of barrier required depends on the location of the foam.
A thermal barrier is a material applied between the spray foam and the interior of the building that is designed to slow the temperature rise of the foam during a fire. This gives occupants more time to escape. According to the International Code Council (ICC), the most common thermal barrier is 1/2-inch gypsum board (drywall). Other materials can be used if they pass a specific fire test, but drywall is the standard for walls and ceilings in occupied spaces.
An ignition barrier is a protective layer that is less robust than a thermal barrier. It is designed to prevent the foam from being ignited by a brief and small fire source, like sparks. These are typically required in limited-access areas like attics and crawl spaces where people are not continuously present. Approved ignition barriers often include:
The market for fire-resistant construction materials is growing, with a report from Fortune Business Insights projecting significant expansion. This trend highlights the increasing focus on safety in building design and material selection.
Bonus Tip: When an intumescent coating is used as an ignition barrier, it must be applied to the thickness specified by the manufacturer for that specific foam product. Applying too thin a layer will not provide the required protection and will fail inspection.
Choosing the right insulation involves more than just its R-value; fire safety is a critical factor. Before starting a project, consider the following:
Bonus Tip: In some specific commercial or industrial applications, foam can be left exposed, but this requires meeting a different, more stringent set of fire tests, such as UL 1715 or NFPA 286. For residential projects, always assume a barrier is needed.
Open-cell spray foam provides excellent thermal insulation and air sealing benefits. Its fire safety performance depends entirely on a code-compliant installation. This means ensuring the foam has a Class A ASTM E84 rating and is properly covered with the right thermal or ignition barrier for its location. Always check the product’s data sheet, understand your local building codes, and work with a qualified professional to ensure a safe and effective result.
If you have questions about the specific fire safety requirements for your insulation project, it is best to consult with a professional. For guidance tailored to your building, Wegner Insulation can provide the necessary details. Contact Anthony at [email protected] or call (406) 654-4636 to discuss your project’s specifications.
A thermal barrier, like 1/2-inch drywall, is designed to keep the foam from reaching its autoignition temperature for at least 15 minutes in a fire. An ignition barrier is a less protective layer designed simply to prevent the foam from igniting from a short-term heat source like a spark.
Like most synthetic materials, burning spray foam can release harmful chemicals. Research from the National Institute of Standards and Technology (NIST) shows that the primary toxicant in many house fires is carbon monoxide, produced by all burning organic materials. A properly installed thermal barrier is the best defense, as it prevents the foam from becoming involved in a fire in the first place.
No spray foam is “fireproof.” All foams are combustible. However, they are formulated with fire retardants to meet the ASTM E84 Class A rating. This rating indicates that the foam resists flame spread and has limited smoke production, but it does not make the material non-combustible.
Ask the installer to specify what thermal or ignition barrier they plan to use for your project and where. This should be clearly stated in your contract. You can also ask for the technical data sheet for the foam product they are using. Finally, a building permit and subsequent inspection by a local building official will confirm the installation is code-compliant.
No, standard latex or oil-based paint is not a fire barrier. The only type of “paint” that can serve as a barrier is a certified intumescent coating designed specifically for this purpose and applied at the manufacturer’s required thickness.