is composite decking fire resistant

Is Composite Decking Fire Resistant?

In Exterior Wood, Tips by Jamie

The deck in your backyard is a common place for a fire to start. So, when you are buying and installing a new deck, you need to think about how fire-resistant the material is. Composite decking is popular because it’s durable and low-maintenance, but is it fire resistant?

Yes, composite decking is fire resistant, and most composite boards are rated Class C or above. Some brands are rated Class A, making them incredibly fire-resistant.

It’s best to look for Class A rated composite decking, if possible. This guide will tell you everything you need to know about composite decking and fire hazards.

What is Composite Decking Fire Rating?

A fire rating is a measure of how well a certain material resists fire. Composite decking is categorized into different classes depending on how fire-resistant it is. This is determined by how long the material will take to ignite and how fast the fire will spread once the material is burning, to give a flame spread rating.

The flame spread rating is calculated by testing the material in a laboratory setting. The specimen is subjected to a controlled fire and the time it takes for the flame to spread is measured and then compared against red oak. It takes five and a half minutes for a flame to travel 19.5 meters along a piece of red oak. This gives a flame spread rating of 100. To test other materials, one end of the sample is set on fire and the time it takes for it to travel 19.5 meters is measured. This is then compared with the red oak to calculate a flame spread rating.

When composite decking is fire rated, it will be split into the following categories:

  • Class A: 0-25 flame spread rating
  • Class B: 26-75 flame spread rating
  • Class C: 76-200 flame spread rating
  • Class D: 201-500 flame spread rating
  • Class E: 500+ flame spread rating.

Is Composite Decking Class A Fire Rated?

Some composite decking is not Class A fire rated and many of the products you find on the market will be Class B or C. However, there are certain brands that are Class A fire rated as they are manufactured with better fire retardant materials. If you are concerned about fire hazards in your backyard, make sure to do your research and find Class A rated decking materials. In some states, like California, this is a requirement anyway. 

What Does Class A Fire Rated Mean?

A Class A rating is the highest possible fire rating for any building material. It means that the material has been tested and found to resist fire for long periods. It is also very unlikely that the fire will spread and get out of control. Other materials with a Class A rating include stone, brick, concrete, and gypsum wallboard.

Class A is split into two categories; A1 and A2. If a material is rated A1, it is not combustible at all and will not provide fuel for a fire. If it is rated A2, there is a tiny chance that it will catch fire but it’s still incredibly unlikely.

Will Composite Decking Catch on Fire?

The plastic in composite decking makes it more of a fire hazard, but manufacturers use fire retardants to counteract this and reduce the chances of composite decking catching fire. If the decking has a Class A fire rating, it will not catch fire or provide fuel. But if it is rated Class B or C, it is combustible, although it will have a limited or minor contribution to the fire.

There are a number of things that can cause a fire on composite decking. If you have a BBQ on the deck, for example, and the grill is not properly cleaned, it could cause a fire. A spark from a cigarette or an errant ember from the fire pit could easily ignite the decking. If you are not careful, you could easily start a fire on your deck, but it shouldn’t spread if the composite has a good fire rating.

Will Composite Decking Melt?

Composite decking is made with a combination of wood fibers and plastic. The plastic in the decking boards is prone to melting at high temperatures. The exact temperature varies depending on the composition of the decking, but polypropylene melts at 160 celsius and PVC melts at 100 celsius. So, if the deck catches fire or it is exposed to a lot of heat from a BBQ or a fire pit, for example, there is a risk of melting.

Are Fire Pits Safe on Composite Decks? OutdoorMaster Fire Pit Mat Upgrade Insulation Cotton 5-layer Design |67" x 60"| Grill Mat/Fireproof Mat/BBQ Pad/Ember Mat 2-in-1 Fireproof Fabric Protect Wood, Lawn Fireproof Pad for Outdoor-Black,L

Fire pits can be used on composite decks, but it is important to take precautions to protect against the heat. Be aware that embers from the fire pit, or the heat from the pit itself, could melt the deck and cause permanent damage. The good news is, you can protect the decking with a fire pit mat. These heat-resistant mats are placed under the fire pit to stop melting and catch flying embers. Check out our list of the best fire pit mats here.

What is the Most Fire-Resistant Decking Material?

Class A rated composite wood is an incredibly safe decking material. If using natural wood, you should look for Fire Retardant Treated (FRT) options. This wood has been pressure treated with fire retardant chemicals that stop the spread of flames if the deck catches fire.

However, the most fire-resistant material you can get right now is Autoclaved Aerated Concrete (AAC) block. This material is made with concrete, water, and an air-entraining agent. It is then placed in a pressure chamber where it is heated to over 100 celsius. The high temperatures make the AAC incredibly strong and fire-resistant. It is also very lightweight and easy to work with, making it a good option for decking.

Final Thoughts

The fire rating is one of the most important things to look at when buying decking materials. This is especially true if you plan to use a BBQ or fire pit on your deck. Always look for Class A rated composite decking if you want to maximize safety.

Read our related composite decking articles: