Wood Fire Treatments: Pressure Treated vs Topically Applied
Posted on: February 24, 2023
Natural wood is a beautiful and versatile building material that has been used in construction for centuries. However, its flammability makes it vulnerable to fire damage, which can be devastating. To mitigate the risks associated with using natural wood in construction (and on exterior applications), there are two approaches to fire protection that are available: pressure-treated fire treatment and topical fire treatment. This article will discuss the differences between these two treatments, their benefits, and their compliance with Class A Fire Rating and Wildland Urban Interface (WUI) regulations.
Benefits of Utilizing a Fire Treatment
As already mentioned, natural wood has been used as a building material for centuries. However, with the increasing concerns of wildfires threatening properties, some have chosen to use alternative building materials that are manufactured for fire resistance.
Some even try to look like wood.
However, although these materials try to appear like the real deal, they can’t replicate an authentic wood product’s natural warmth and beauty.
Now, with the development and use of these cutting-edge fire retardants, you can utilize wood and have the confidence your project is protected the next time fire is threatening.
Additional benefits include:
- Code compliance. In many jurisdictions, fire treatments are required by building codes for certain types of construction. Compliance with Class A Fire Rating and WUI regulations can help ensure the safety of the building and its occupants.
- Durability. Pressure-treated fire treatment provides long-lasting protection against decay.
Why Is The Treatment’s Fire Rating Important?
The rating of the fire-retardant solution you decide to use reflects its effectiveness against flame spread and smoke development. The higher the rating in each of these categories the more protective the material is in a fire event so long as the materials are installed in accordance with the International Build Code.
A specific fire rating or designation may be required in some jurisdictions. In that case, you want to ensure the fire solution you choose on meets the requirements for your area. Consulting with local fire code officials is the best practice to ensure compliance and to make sure your structure is safe.
What Are The Fire Rating Classifications?
The following is a basic overview of the fire rating classifications. The index values measure how fast and how far flame will spread over a certain material.
Class 1 (or Class A) Fire Rating
A “Class A” or “Class 1” fire rating is a material’s best fire rating. Materials with this rating do not burn well and have a flame spread index of 0-25.
Class 2 (or Class B) Fire Rating
A “Class B” or “Class 2” fire rating is a material’s second-best rating. The flame spread index of materials with this class rating fall between 26-75.
Class 3 (or Class C) Fire Rating
A “Class C” or “Class 3” fire rating is the third best rating a material can achieve. The flame spread index of materials with this class rating fall between 76-200.
Note: The above rating classifications are established through specific testing processes established by the American Society of Testing and Materials. The ASTM E-84 is the standard test method for assessing the surface burning characteristics of building products to explore how the material might contribute to flame spread in the event of a fire. The test reports the tested product’s Flame Spread index and Smoke Developed index.
Wildland Urban Interface (WUI) Compliance and Standards
In specific areas under higher than normal threats from wildfires, materials and the application of fire retardant chemicals that meet WUI standards may be required.
According to the U.S. Fire Administration, “The WUI is the zone of transition between unoccupied land and human development. It is the line, area or zone where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels.“
To achieve both a Class A rating and meet WUI standards, a material must be ignition resistant. Having the ability to resist ignition from flying embers or fire radiation during a wildfire.
Pressure-Treated Fire Resistance Treatment
The process of applying a pressure-treated fire treatment involves placing the wood in a vessel, then injecting the chemical preservative under high pressure. This process forces the chemical deep into the wood fibers, providing long-lasting protection against decay, insects, and fire.
A highly durable and fire-resistant material that can be used in a variety of construction applications.
Materials armed with pressure-applied fire treatment are an ideal choice for applications that require either Class A fire rating compliance, or Class A fire rating in combination with Wildland Urban Interface (WUI) compliance requirements.
For instance, the products we offer (in combination with our Fireline treatment) have been a popular solution to meet these requirement needs.
Is “Pressure-Treated” the Same as Fire-Treated?
Note, the use of pressure is a part of this fire retardant application process; but, “pressure-treating” wood doesn’t necessarily make it a non-combustible material. For instance, the “pressure-treated” wood at your local lumber yard might have a higher resistance to rot and decay; but, it doesn’t mean it was additionally treated for fire resistance.
Topical Fire Treatment
Topical (or spray-applied) fire treatment involves the application of a fire-retardant chemical to the surface of the wood. This chemical creates a barrier that prevents the wood from catching fire. Topical fire treatment is generally less expensive than the pressure-treated alternative.
The topical treatments are applied to the surface of the wood after it has been milled; but, before it has been finished and installed.
Some topical treatments carry a Class A Fire rating and are accepted in wildfire-prone areas of the country.
For instance, the spray-applied fire resistant treatment that we offer carries a Class A rating, is environmentally friendly, and is applied by our in-house production team.
Ultimately, the local authority having jurisdiction mandates code compliance pertaining to fire resistant building materials and what is required in your building area.
Will Fire Treatments Affect The Look Of Our Wood Siding?
As a result of the treatment process, we do see a slight finish variation after it has received the pressurized fire treatment.
Maybe a shade or two darker when finished as compared to the material of the same product line and finished color that wasn’t treated.
Our spray-applied treatment can have a very subtle color change when combined with some of our stains. With that in mind, control samples may be needed.
This is great for areas where only Class A is required; however, if WUI compliance is required in your area, the pressure-applied solution is your only option.
Which Fire Retardant Solution is Best For You?
Choosing the best fire retardant-treated wood solution for you and your project depends on a few factors.
- Your budget. Pressure-treated fire retardant is more expensive than the spray-applied option.
- Your location. A fire retardant with a Class A rating is the only requirement in some areas. WUI compliance (in addition to a Class A rating) is required in other areas. You need to confirm with the authority with jurisdiction in your building zone.
- Your timeline. When it comes to fire protection treatments that we provide, we apply the spray-applied protection in-house whereas pressure-treated is completed in another facility. So, ordering material with our Fireline treatment will affect your lead time.
While eliminating wildfires is not possible, there are viable options, while still using a renewable product like natural wood to help protect your property. Home hardening, which includes implementing fire-resistant exteriors and defensible spaces around structures, is a great first plan of action.