What Is Fire-Retardant Treated Wood?

As long as wood has been used in building human structures, fire has always been a concern. Wood is naturally flammable and wood structures can burn fast and furious once they ignite. Fire codes and regulations have come a long way in helping prevent disasters and fire-retardant treated wood has played a big part in that prevention. Let’s take a look at all there is to know about fire-retardant treated wood and how it can be used in building construction. 

Fire-retardant treated wood: What Is It?

Fire-retardant treated wood (FRTW) is wood that has been treated with a chemical process that makes it more difficult for the wood to burn if exposed to flames.

The process cuts down on reaction-to-fire parameters, including:

  • Ignitability–how easily something can catch fire
  • Heat release–the amount of heat energy released from something during combustion
  • Flame spread–the movement of flame over the surface of something during the burning process
  • Smoke production–the amount of smoke produced when something burns

The goal of fire-retardant treated wood is to lessen these reaction-to-fire effects on wood and make it a safer product to use for building construction. 

How Is Fire-retardant Treated Wood Made?

Fire-retardant wood products are generally made by permeating wood with fire-retardant chemicals through a pressure process. The result is a wood product that contains a mixture of chemicals that act to slow down wood’s natural combustion process, making it more fire resistant.

The cut and prepared wood, either lumber or plywood, is first kiln-dried to increase its durability and guard against warping, twisting, or buckling. It also prepares it for the pressure process.

Then, the wood is treated with fire-retardant chemicals in a retort chamber. This chamber is constructed to create a vacuum system where the mixture of fire-retardant chemicals can be infused deep into the wood fibers.

It is important for the entirety of the wood to be treated to meet most building codes. Uneven treatment can result in uneven fire-resistant capabilities.

Manufacturers have quality control measures in place to ensure treated wood meets standard requirements, including the wood’s ability to:

  • Resist ignition
  • Slow the spread of flames
  • Maintain an acceptable level of structural integrity under burn conditions 

What Is Fire-Retardant Wood Treated with

The treatment process is done at the manufacturing level and the exact mixture of chemicals used in FRTW manufacturing depends on the specific manufacturer. Most fire-retardant chemical mixtures are proprietary. The process timing varies according to size, thickness, and type of wood being treated. Not all types of wood can be treated with fire-retardant chemicals. 

The most common chemicals used in fire-retardant treatments are mono- and diammonium phosphate, ammonium sulfate, borax, boric acid, zinc chloride, and aluminum sulfate. 

What Building Applications Use FRTW?

According to 2021 data from the National Association of Home Builders, 92% of new homes are wood framed. This leaves a considerable amount of wood that goes into building the average home, a material that is inherently flammable. Both plywood and building lumber is available with fire retardant treatments. These materials make up the majority of wood construction  elements for most residential construction.

The chemical, physical, and mechanical properties of FRTW differ from untreated wood. This makes them an ideal product suitable for specific building applications. These application specifics are tied to building standards, codes, and regulations. 

Building Standards, Codes, and Regulations 

Fire-retardant treated wood materials and building products are classified and certified according to their level of fire resistance. The quality control tests, described above, and international standards and building regulations determine what level of resistance corresponds with what FRTW product classification. It is important to follow these guidelines to ensure sufficient fire protection and safety. What building applications these classified products can be used for is determined by local building codes.

Building safety standards differ state to state and city to city. This means that FRTW building standards are dependent on specific building codes relevant to your jurisdiction. Knowing and understanding the building codes for where you are building is essential. An understanding of different FRTW types can make deciphering these standards and codes easier. 

The Two MainTypes of FRTW

Two main types of FRTW are manufactured to be code compliant. These are interior products that are not meant to be exposed to the elements and exterior products that are made to be exposed to the elements. Exterior products are designed to be non-corrosive and endure both excessive moisture and heat. Interior products are also tested for durability and to hold up under high-moisture and high-heat conditions. 

Interior Uses

Some standard choices for interior use of fire-retardant treated wood products include:

  • High-traffic areas, such as hallways and mezzanines in high-density developments
  • Ceiling supports, interior beams, and load-bearing walls in residential buildings
  • Roof trusses, sheathing, and rafters
  • Floor joists, sheathing, and sub-floors
  • Stairways and steps
  • Wall sheathing, studs, and partition walls
  • Exhibition stands and stages
  • Storage areas 

Exterior Uses

Exterior FRTW products have standard applications that include:

  • Exterior decks and balconies
  • Exterior stairways and railings
  • Siding, molding, trim, soffit and fascia
  • Roof sheathing and shingling
  • Support structures and framing
  • Outbuildings, stables, workshops, sheds and barns 

Wood Durability: How Long Does Fire-retardant Treated Wood Last?

Fire retardant treated wood has a very high durability rating. Most manufacturers will issue warranties lasting up to 50 years for their fire-retardant treated wood products. This is often the average lifespan on the average building. A cost analysis of using FRTW products will often show that they are a cost-effective way to not only meet building code standards but often surpass them.

In contrast, wood fire retardant paint, coatings, and intumescent coverings have a much shorter lifespan. Although, it is usually easier and less expensive to re-apply these products throughout the life of the building. 

Ensuring Durability

There are also things that are within your control that can help ensure the durability of fire-retardant treated wood. 

Choose Quality Products

One thing that you are in control of when it comes to fire safety is in choosing the right products. Make sure to choose quality FRTW products that are tested and documented to meet international standards according to their effectiveness and durability as well as for their planned purpose. 

Follow the Manufacturers Recommendation

Another thing that you are in control of is how you use the products you choose. Reputable manufacturers will provide recommendations and guidelines on how to use and properly maintain fire retardant treated wood products. Wood maintenance, including any required re-treatment, is important if you want to keep it doing what it is built to do–resist fire. 

Look for Proper Third-Party Certifications

Understanding and checking for FRTW certifications for the products you use is another layer of protection and peace of mind. Look for third-party certifications that show how well the product performs over time to confirm that the product will do what it says it will do for as long as you need it to.

Environmental Impact of FRTW Products

Changing the makeup of wood, which is naturally highly flammable, into something that resists flames, relies on chemical treatments, as explained in this article. Knowing this does make a lot of people wonder what the environmental impact of using those chemicals might be. As with all manufacturing, transportation of raw materials and the energy used to create building products all have an environmental impact. Some other studies have also shown some environmental impact of fire-retardant chemicals, but these impacts are shown to be less than those associated with transportation and the manufacturing process. Overall, precautions and regulations surrounding the use of these chemicals need to be adhered to to prevent unnecessary danger.

On the flip side, is the environmental impact of burning carbon-rich materials, such as wood. When wood burns in a fire it releases the carbon trapped in the wood into the air. This process contributes to the environmental effects of carbon in the atmosphere that is associated with climate change. Lowering the instances of fire, through the use of FRTW products can help prevent these effects. 

Fire-retardant Treated Wood: The Last Word

Fire safety is not something to take lightly. When fires break out they can cause a lot of property damage and, more importantly, cost lives. When applied to their certified use and adhering to quality standards, Fire-retardant treated wood products can be a durable and cost-effective way to meet building code standards and even surpass them in constructing fire safe structures.

Check out more information on how to fireproof wood or contact Fire Retardants Inc to improve on your fire safety and construction know-how.