Fiber Reinforced Plastic (FRP) walkways are increasingly used to provide safe access on commercial rooftops with solar installations. However, a key concern for these rooftop walkways is fire resistance, since many building insurers and codes prohibit adding flammable materials on roofs. In the event of a rooftop fire (for example, caused by electrical faults or maintenance activities), any combustible walkway could accelerate fire spread. Therefore, FRP walkways on solar roofs must be formulated as fire-retardant to meet strict standards and insurance requirements. Installing properly rated FRP walkway panels ensures compliance and safety without sacrificing the benefits of FRP like light weight and corrosion resistance.
FRP grating walkways (yellow) installed on a metal rooftop provide a safe, non-slip access route for solar panel maintenance. Fire-retardant FRP panels offer flame spread ratings similar to noncombustible materials, satisfying roof insurance requirements.
Why Fire Retardancy on Rooftops is Crucial
Rooftop solar projects often span large areas on building roofs. Fire safety is paramount in these installations because a roof fire can threaten the entire building. Insurance policies and fire codes typically prohibit combustible materials on roofs or require that any added components have very low flame spread characteristics. In practice, this means that walkway materials must be fire-retardant so they do not introduce new fire hazards. This indicates that a properly fire-rated FRP walkway is considered a minimal fire load. If an FRP walkway were not flame-retardant, it could violate insurance conditions and potentially void coverage due to adding a fuel source on the roof.
Another reason fire retardancy is vital is to maintain the building’s overall fire rating. Commercial roofs are often required to have a Class A fire-rated assembly (the highest level) to resist external fire exposure. Any accessory on the roof, including walkways, should not diminish that rating. By using FRP walkways with built-in fire resistance, facility owners ensure the rooftop system remains compliant with fire safety regulations and does not hinder firefighting. Ultimately, prioritizing fire-retardant materials on solar rooftops protects both property and personnel, aligning with insurance, safety, and code requirements.
Fire Safety Standards for FRP Walkways
To evaluate and ensure the fire resistance of FRP materials, several fire safety standards are used in the industry. The most relevant standards for rooftop FRP walkways include:
- ASTM E84 – Surface Burning Characteristics:This test (often called the Steiner Tunnel test) measures a material’s flame spread index (FSI) and smoke development index (SDI) when exposed to fire on one surface. Building codes categorize materials based on E84 results: Class A (Class 1) is the most fire-resistant rating with FSI ≤ 25 and SDI ≤ 450 . Class B and C have higher flame spread allowances. Roofing and construction often demand Class A materials. In fact, many building codes explicitly require FRP grating to pass ASTM E84 for use in buildings . Achieving a Class A rating means the FRP walkway will not significantly spread flames across its surface.
- UL 94 – Flammability of Plastic Materials:UL94 is a standard that classifies how plastics burn on a small scale (vertical or horizontal position). For instance, a UL94 V-0 rating indicates that the material self-extinguishes quickly after being ignited vertically, with no dripping flaming particles. This is a stringent classification signifying superior self-extinguishing properties . FRP walkway components (made of polymer resin and fiberglass) are often tested to UL94 to ensure that if a fire starts, the material will not continue to burn actively once the heat source is removed.
- ASTM D635 – Rate of Burning (Horizontal):This is a small-scale test that checks if a plastic sample will self-extinguish when burned in a horizontal orientation. Many FRP products are designed to be “self-extinguishing” per ASTM D635, meaning they stop burning on their own after a short distance/time. Meeting ASTM D635 criteria is commonly required for FRP gratings and gives an added assurance of the material’s basic fire suppressing behavior.
- Other Relevant Standards:Depending on the project location or industry, there may be additional standards. For example, NFPA standards (such as NFPA 130 for transit applications) specify fire performance for composites in certain uses, and BS 476 or EN 13501 standards govern fire performance in Europe (with ratings like BS Class 1 or Euroclass Bfl-s1 for flooring applications) . While these might not be directly mandated for a rooftop solar in the U.S., they indicate that FRP materials can be engineered to meet stringent fire criteria globally. Some FRP walkway products advertise compliance with multiple fire standards (ASTM E84 Class A, UL94 V-0, EN13501, etc.) to serve international markets .
In summary, ASTM E84 Class A rating is usually the baseline requirement for rooftop installations in the U.S., ensuring low flame spread. A high-quality FRP walkway will typically also meet UL94 V-0 and be self-extinguishing, providing multi-faceted fire safety assurances. These test ratings give engineers and insurers confidence that the FRP material will perform safely under fire conditions.
How FRP Walkways Meet Fire-Retardant Standards
FRP (Fiber Reinforced Plastic) is a composite of a polymer resin (plastic) matrix reinforced with fibers (usually glass fibers). By default, the resin component (especially common types like polyester or vinyl ester) is organic and can burn. To make an FRP walkway fire-resistant, manufacturers employ special resin formulations and additives during production:
- Fire-Retardant Resin Systems: The choice of resin greatly influences flammability. Standard orthophthalic polyester resin is the most basic and tends to be the least fire-resistant. For better fire performance, isophthalic polyester (Type I) or vinyl ester resins are often used, as they have improved fire and smoke behavior when compounded with additives . In very high fire-risk environments (like offshore platforms or transit systems), a phenolic resin (Type P) may be used for FRP grating, because phenolic FRP inherently has extremely low flame spread and smoke production . Phenolic-based FRP emits a char layer and minimal smoke when exposed to flame, making it suitable where the absolute highest fire performance is needed .
- Fire-Retardant Additives and Fillers:Most fire-resistant FRP walkways rely on additives mixed into the resin. A common additive is aluminum hydroxide (Al(OH)_3), also known as alumina trihydrate, which releases water when heated, thereby quenching flames and reducing smoke. Manufacturers often prefer aluminum hydroxide as a filler over cheaper fillers like calcium carbonate, specifically because it imparts significant flame retardance and smoke suppression . These additives raise the limiting oxygen index of the FRP (meaning a higher concentration of oxygen is required to sustain combustion). For instance, an FRP molded grating might be formulated with an oxygen index ≥ 28% and achieve a UL94 V-0 rating due to these additives . Other chemical flame retardants (brominated or halogenated compounds, phosphorus-based additives, etc.) can also be used to meet fire specs, though there is a trend toward non-halogenated solutions for environmental reasons.
- Self-Extinguishing Behavior: Through the right resin and additive combination, FRP gratings can be made self-extinguishing. As noted, products are available that meet ASTM D635 requirements for self-extinguishing and UL94 V-0, meaning they will not continue burning on their own . For example, one manufacturer’s specification for pultruded FRP grating calls for a flame spread index ≤25 (Class A), UL 94 V-0 rating, and self-extinguishing per D635 as mandatory performance criteria . This triple certification ensures the material will have very limited flame spread, produce relatively low smoke, and quickly snuff out if ignited.
- Testing and Quality Control: To verify compliance, reputable FRP walkway suppliers will have their products tested by independent labs. They can provide ASTM E84 test reports showing the flame spread and smoke index numbers. A flame spread index in the low twenties or below (≤25) is the goal for a Class A material. Many fire-retardant FRP gratings actually test much lower than 25 for flame spread , often in the range of single-digits to low teens, effectively making them comparable to non-combustible materials in surface-burning behavior. Smoke developed index is also measured; staying under 450 is required, and lower is better to minimize toxic smoke in a fire. Engineers should review these test reports or material data sheets to ensure the FRP meets the needed ratings.
By carefully engineering the resin mix and reinforcement, FRP walkway panels can be made to meet stringent fire standards without losing their structural integrity. The fiberglass itself is not flammable (glass fibers will not burn), so the focus is on the resin. Using the right fire-retardant resin system and additives yields an FRP product that will char or self-extinguish under flame, rather than fuel a growing fire. The result is a composite walkway that satisfies code requirements for flame spread and smoke, enabling its use on rooftops in compliance with insurance rules.
Conclusion
FRP walkways have emerged as a popular solution for rooftop solar installations, offering a way to protect the roof and facilitate maintenance access. By choosing fire-resistant FRP walkways, solar project developers and facility managers can reap the benefits of fiberglass composites (light weight, strength, corrosion resistance) while fully complying with fire safety requirements. The importance of fire retardancy cannot be overstated: insurance and code compliance depend on using materials with minimal combustibility on the roof. Thanks to advanced resin formulations and additives, modern FRP grating products can achieve Class A flame spread ratings and self-extinguishing performance, making them safe for use even in critical applications.
Contact Solaracks for more details if your rooftop solar project has the fire safety requirements.