HomeOutdoor Living BlogFacts About Flame Spread Rating & Why It Matters

Facts About Flame Spread Rating & Why It Matters

August 5, 2022
TimberTech PVC decking in Weathered Teak with a Class A Flame Spread Rating

Whether building or renovating a home or an outdoor living space — or both — you may have come across the term “flame spread rating” in your search for building materials. Flame spread rating is a designation that indicates how fast a certain material will burn and how far the flame will spread if caught on fire. This is especially important for homes in fire-prone areas such as California or Nevada. Materials that catch fire and burn more slowly are considered safer for these areas.

Rating for flame spread can apply to any building material that is properly tested, from concrete to siding to decking.

What Is Flame Spread Rating?

Flame spread rating measures how fast and far a flame spreads over a certain material.

Testing for flame spread rating involves burning materials under controlled conditions and measuring the speed and extent of flame spread. The resulting number is the flame spread index.

Flame spread ratings range from an index of 0-200, with Class A being the best with an index of 0-25, Class B with an index of 26-75, and Class C with an index of 76-200. Lower classes (indices higher than 25) indicate that flames spread more quickly and covered a greater distance than compared to Class A flame spread rated material.

What to Know

A numerical reference that measures how fast and far a flame spreads during a 10-minute test.

Flame Spread Index of 25 or less; the best possible rating, awarded to fire-resistant building products.

Poolside composite deck with Class A Flame Spread Rating in California

What Is a Good Flame Spread Rating?

The best rating is a Class A Flame Spread Index.

Materials with a Class A Flame Spread Index are those that hit a certain threshold (an index of 25 or less), indicating less flame spread and/or slower time to travel as compared to other materials.

Where Does Class A Flame Spread Index Rating Come From?

Testing to establish a flame spread index was developed in 1944 by Al Steiner of Underwriters Laboratories. It has since been referenced as UL 723, or the Surface Burning Characteristic of Building Materials test. The American Society for Testing Materials adopted the same test into its own standards, referred to as ASTM E84, the Standard Test Method for Surface Burning Characteristics of Building Materials. Both UL 723 and ASTM E84 are referenced in building codes.

Ratings for flame spread are incorporated into the model building codes as published by the International Code Council (ICC) Building codes published by the ICC include the International Building Code (IBC), the International Residential Code (IRC), and the International Fire Code (IFC) to name a few.

These codes detail:

  • Materials used in different types of construction
  • Fire protection systems (sprinkler system requirements and design)
  • Means of egress (ways to leave a building or other structure)
  • And much more, all focused on safety in the built environment

Understanding WUI-Compliance in Relation to Flame Spread Rating

A second-story lakeside composite deck with the best flame spread index

Along with flame spread rating, you may have heard of WUI-compliance. WUI stands for “Wildlife Urban Interface” and was adopted by the California Building Commission over a decade ago. WUI designates areas that are within or adjacent to communities deemed “at-risk” for wildfires. WUI-compliant building products refer to those below a certain threshold for flame spread.

Some jurisdictions designated as Wildlife Urban Interface (WUI) areas, especially in California, Colorado, and Nevada, require that certain building products meet the Class A Flame Spread Index rating.

However, it’s important to note that just because a product is WUI-compliant, does not mean it has a Class A Flame Spread Index rating — and vice versa. In order for a material to meet the standards for a Class A Flame Spread Rating and WUI compliance, it would need to undergo specific testing for each classification.

TimberTech Decking: A Better Choice for Fire-Prone Areas

Curved composite decking with Class A Flame Spread Rating

When it comes to decking, your options go far beyond wood treated with fire-resistant chemicals, which often aren’t the best choice for fire-prone areas. TimberTech PVC and composite decking are designed to help you live your best life outdoors, worry-free.

We offer multiple collections with Class A Flame Spread Rating or WUI-Compliance — or in the case of the Vintage Collection, both. And the best part? Our decking also features a range of realistic wood aesthetics, so you don’t have to compromise on the look you love.

Vintage Collection®·        Class A Flame Spread Rating
·        WUI-Compliant
Landmark Collection·        Class A Flame Spread Rating
Harvest Collection®·        WUI-Compliant
Porch Collection·        WUI-Compliant
Reserve Collection (Fire-Resistant Reserve SKUs Only)·        WUI-Compliant

Want the Best Decking for Fire-Prone Areas?

Choose the Vintage Collection, which features both a Class A Flame Spread Rating and WUI-Compliance for the best decking in fire protection.

TimberTech composite deck with the best flame spread rating built in a woodland area

Build a Better Deck for Fire Zones With TimberTech

With WUI-Compliant and Class A Flame Spread Rating options from TimberTech, you can build a better deck for fire-prone areas. Explore different color and texture options across our Class A flame spread rated and WUI-compliant PVC and composite decking lines to find the real wood look that suits you best.

See & feel the TimberTech advantage

Our capped polymer and capped composite decking lines combine recycled material with all the beauty of traditional wood.

Scroll to Top