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Structural Solutions for Fire-Resistant Roof Sheathing

In fire-prone geographies, such as wildland-urban interface (WUI) areas, fire protection for roofs may be a critical part of a comprehensive approach to slowing the spread of fire and fire damage in homes. A fire classification roof system is required in WUI areas to protect your build and clients’ peace of mind—and with the right products, the installation process can be simple.

Let’s take a look at fire-resistant roof sheathing and how it can help you approach building better in fire-prone areas.

Do Roofs Need to Have Fire Resistance From the Exterior?

In areas that are prone to wildfires, particularly WUI zones, meeting ignition-resistant construction guidelines is very important. Choosing to include fire-resistant OSB roof sheathing can help add protection without sacrificing ease of installation and design. Be mindful of your client’s concerns regarding roofing systems, no matter the area or code requirements. This can help you make decisions for the build that will offer them extra assurance. 

“If embers or flames find their way through to the roof sheathing, it’s not a bad idea to have fire-resistive qualities in your roof sheathing,” says Scott Johnson, Construction Services Manager, LP Building Solutions. “For roofs, it’s key to take steps to prevent flames or floating embers from finding their way to the substrate.” That’s why, if those efforts fail, having the redundancy of a fire-resistant roof sheathing can help protect the integrity of the structural framing below, which could help minimize repair costs following a wildfire event.

Roof Fire Classification Requirements

Roof fire classifications are required depending on the Ignition-Resistant Construction requirements:

  • Class 1 Ignition-Resistant Construction assumes the most severe exposure and requires roof assemblies to comply with a Class A rating when tested in accordance with ASTM E108 or UL 790.
  • Class 2 Ignition-Resistant Construction requires a minimum Class B rating when tested in accordance with ASTM E108 or UL 790, or an approved noncombustible roof covering.
  • Class 3 Ignition-Resistant Construction has the least severe exposure but does require a minimum Class C rating when tested in accordance with ASTM E108 or UL 790, or an approved noncombustible roof covering.

When builders choose to pair noncombustible roofing materials with fire-rated sheathing, the build’s fire-resistive capabilities increase.

How Thick Should Roof OSB Be?

There are a few factors that determine thickness for fire-rated OSB under a roof. The span of the roof trusses (or rafters) and snow load should be considered, as well as whether edge support is used. However, always consider the type of roofing materials your OSB will need to support in addition to other measurements and designs for your build.

Many OSB products come in performance categories that can fit your build’s needs. For example, LP® FlameBlock® Fire-Rated Sheathing comes in 7/16˝, 15/32˝ and 19/32˝ thicknesses.

LP FlameBlock

Choose LP® FlameBlock® Fire-Rated Wall and Roof Sheathing

For fire-rated OSB under roof materials, LP® FlameBlock® Fire-Rated Sheathing is a great choice if you’re building in fire-prone areas. LP FlameBlock panels combine flame-spread and burn-through resistance in a single panel.

“Providing fire resistance under the roofing adds redundancy and offers another layer of protection,” Johnson adds. “If flames or an ember gets through, it comes in contact with the ignition-resistant layer of the fire-resistant sheathing.”

LP FlameBlock panels are a cost-effective addition to your build, and the benefit they add far outweighs any initial upfront cost. “If you experience a wildfire, you’ll most likely have damage,” Johnson says. “But the goal is to minimize the extent of the repairs and not have to replace the whole structure. The key is to use construction practices that try to limit the repairs after a wildfire event, such as replacing the siding or exterior roof materials. Using a fire-resistant roof sheathing helps protects the structural integrity of the house.”

Johnson also recommends ensuring your build follows all guidelines to prevent fire damage, such as providing defensible space and using products approved for use in WUI areas. “The goal is to take steps to try and minimize the amount of repair that would be required after a wildfire event,” he adds.

By bolstering a build’s fire-resistant capabilities with fire-resistant roof sheathing like LP FlameBlock panels, you can offer your clients increased peace of mind and build better in fire-prone geographies.

Find out more information about our fire-rated sheathing.

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