Wood is a combustible building material, but some wood species and wood products can provide better fire performance than others. Fire-resistant wood is a general term used for wood that has been selected, treated, or tested to provide improved resistance to flame spread or fire.
There is an important difference between naturally fire-resistant wood and fire-retardant-treated wood. Some dense hardwoods can achieve favorable fire-test results, while other wood products are chemically treated to reduce flame spread.
However, no ordinary piece of wood should automatically be considered fireproof. The actual fire performance depends on the wood species, product, thickness, moisture content, finish, installation, and testing method.
For construction projects, always check the fire rating of the specific product, rather than choosing a wood species based only on its name.
What Makes Wood More Fire Resistant?
Wood species with higher density can sometimes show different burning characteristics from lighter woods. Dense hardwoods may take longer to ignite and can develop a protective char layer during burning.
However, density alone does not determine whether a wood product meets a particular fire-rating requirement.
For building materials, fire performance may be evaluated using standardized tests such as ASTM E84, which measures flame spread and smoke development. Under ASTM E84 classifications, a flame-spread index of 25 or less corresponds to Class A.
Types of Fire-Resistant Wood
There are two main approaches to improving the fire performance of wood:
1. Naturally Dense Wood Species
Some dense hardwoods can demonstrate relatively favorable fire performance because of their density and combustion characteristics.
Examples include:
However, fire performance can vary between products and should be verified with test data for the actual material.
2. Fire-Retardant-Treated Wood
Fire-retardant-treated wood, commonly called FRT wood, is wood that has been treated with fire-retardant chemicals to reduce flame spread.
The treatment is normally introduced into the wood under controlled manufacturing conditions. For applications requiring a specific fire classification, the treated product must meet the relevant testing requirements.
Ipe Wood
Ipe is an extremely dense tropical hardwood commonly used for decking, outdoor structures, and other demanding applications.
Ipe has excellent resistance to decay and insects and is also known for its high density and hardness.
Some published technical data reports Class A fire performance under ASTM E84 for Ipe.
Ipe Pros and Cons
Pros
- High density: Ipe is extremely hard and dense.
- Durable: It has excellent resistance to decay and insects.
- Fire performance: Certain Ipe products have achieved Class A ASTM E84 results.
- Low maintenance: Properly installed Ipe can require relatively little maintenance.
Cons
- Expensive: Ipe is generally more expensive than many common decking woods.
- Difficult to work: Its high density makes cutting, drilling, and machining more difficult.
- Heavy: Ipe is significantly heavier than many common softwoods.
Cumaru Wood
Cumaru, sometimes called Brazilian teak, is another dense tropical hardwood used for decking, flooring, siding, and outdoor construction.
Like Ipe, Cumaru is extremely hard and dense. Technical data reports Class A ASTM E84 fire performance for Cumaru, although the result should always be verified for the specific product being purchased.
Cumaru Pros and Cons
Pros
- Very durable: Its high density provides good resistance to wear and decay.
- Good outdoor performance: It is commonly used in demanding exterior applications.
- Fire performance: Some Cumaru products have achieved Class A ASTM E84 results.
- Attractive appearance: Cumaru generally has warm brown to reddish-brown tones.
Cons
- Hard to work: Its high density can make cutting and drilling difficult.
- Heavy: It is considerably heavier than many common decking species.
- Color changes: Exposure to sunlight can cause the wood to change color over time.
Massaranduba
Massaranduba is a very dense tropical hardwood commonly used for outdoor decking and other demanding applications.
Its high density provides good resistance to wear, insects, and decay. Some technical sources report Class A fire performance for Massaranduba, but fire classification should be confirmed using documentation for the actual product.
Massaranduba Pros and Cons
Pros
- Very hard and dense
- Good outdoor durability
- Attractive reddish-brown appearance
- Good resistance to wear
Cons
- Difficult to cut and drill
- Heavy
- Can be more expensive than common softwoods
Redwood and Fire Resistance
Redwood is well known for its natural resistance to decay and insects, but it should not automatically be described as fire-resistant.
Its fire performance depends on the specific material and test. For example, published decking comparisons distinguish Redwood from Ipe in ASTM E84 fire classification.
Therefore, if a project has a specific fire-rating requirement, do not select Redwood simply because it is naturally durable.
Meranti and Fire Resistance
Meranti is widely used for furniture, doors, window components, molding, and plywood. It is relatively easy to work and is available in several species and grades.
However, untreated Meranti should not automatically be classified as fire-resistant. Research on Meranti has examined ways to improve its fire performance through treatments such as fire retardants and thermal modification.
If fire performance is important, choose a tested or appropriately treated Meranti product rather than relying only on the wood species.
Natural Wood vs Fire-Retardant-Treated Wood
| Feature | Dense Natural Wood | Fire-Retardant-Treated Wood |
|---|---|---|
| Fire performance | Depends on species and product | Specifically treated to reduce flame spread |
| Chemical treatment | Not necessarily | Yes |
| Fire rating | Must be verified | Must be verified |
| Appearance | Natural wood appearance | Depends on treatment and finishing |
| Outdoor suitability | Depends on species | Depends on treatment and product |
| Best for | Applications where natural wood is desired | Projects with specific fire-performance requirements |
Is Fire-Resistant Wood Fireproof?
No.
Fire-resistant does not mean fireproof.
Even dense hardwoods can burn when exposed to sufficient heat and flame. A fire rating indicates how a specific material performs under a defined test; it does not mean the material cannot catch fire.
This distinction is particularly important in construction. If a building code requires a specific fire rating, use a product with documented test results rather than relying on a general claim such as “fire-resistant wood.”
How to Choose Wood for a Fire-Prone Area
If fire performance is important, consider the following before purchasing wood:
- Check the actual fire rating.
- Ask for the manufacturer’s test report.
- Check the applicable building code.
- Consider the complete assembly, not just the wood species.
- Check the thickness and installation method.
- Determine whether fire-retardant treatment is required.
- Consult the local building authority when required.
A piece of wood that performs well in an individual test does not necessarily mean an entire wall, deck, roof, or structural assembly has the same fire rating.
Frequently Asked Questions
What is the most fire-resistant wood?
There is no single wood species that can be called the most fire-resistant for every application. Some dense hardwoods, including Ipe and Cumaru, have demonstrated favorable fire-test performance. Certain products have achieved Class A ASTM E84 results.
Is Ipe wood fire resistant?
Certain Ipe products have achieved Class A under ASTM E84, but the rating applies to the tested product and conditions. Always verify the manufacturer’s current test documentation for the material you plan to use.
Is Cumaru fire resistant?
Cumaru is a very dense tropical hardwood, and some products have achieved Class A ASTM E84 results. However, fire performance should be verified for the specific product.
Is Redwood fire resistant?
Redwood should not automatically be considered fire-resistant. Its fire performance depends on the specific product and test results.
Can wood be made fire resistant?
Yes. Wood can be treated with fire-retardant chemicals to reduce flame spread and improve fire performance. Fire-retardant-treated wood must meet the applicable testing requirements for its intended use.
Is fire-resistant wood completely fireproof?
No. Fire-resistant wood can still burn under sufficient heat and flame. A fire rating describes performance under a particular standardized test; it does not mean the wood cannot burn.
Final Thoughts
Fire-resistant wood is a useful option when fire performance is an important consideration, but not all wood species should be labeled fire-resistant simply because they are dense or naturally durable.
Ipe and Cumaru are examples of dense hardwoods for which Class A ASTM E84 results have been reported for specific products. Fire-retardant-treated wood is another option when a project requires documented flame-spread performance.
Before choosing wood for a fire-sensitive application, check the actual product rating, test standard, thickness, treatment, and building-code requirements. For construction projects, the fire performance of the complete assembly can be just as important as the wood itself.