Fire Ratings, for Building Products

Many homes and buildings within Montana’s alpine environment are subject to wildfires and severe weather, depending on the region and time of year. Building codes allow contractors, engineers, and architects to have a comprehensive list of requirements to serve their local area in terms of safety and sustainability. These codes include ASTM and WUI standards which are in place to help protect your home during wildfire.

What are fire ratings? 

Fire ratings for building materials is a way to classify the material’s overall ability to support and propagate fire and also indicate the smoke produced by the material.  

What are the different ratings? 

Class A:

Class A roofing assemblies are defined as being effective against severe fire test exposure. This generally involves fire-resistant roofing materials and ember/flame-proof construction. 

  • Maximum flame spread of 6 feet.
  • Can withstand a burning mass of 1 sq.ft. and 4.4 pounds.
  • Last 2-4 hours before ignition.
  • Resist 15 cycles of a gas flame turned on and off.

Examples of materials classified by ASTM 108 as class A include brick, clay tiles, and some asphalt shingles.

Class B:

Must resist a continuous gas flame for 10 minutes. This is the maximum requirement by the IBC.

  • Maximum Flame spread of 8 feet.
  • Withstand a burning mass measuring 6” X 6” and weighing 1 pound.
  • Last 1 hour before ignition.
  • Resist three cycles of a gas flame turned on and off.

Examples include pressure-treated shakes and shingles, some asphalt shingles, and slower burning whole wood materials.

Class C:

Must resist a continuous gas flame for 4 minutes.

  • Maximum flame spread of 13 feet
  • Withstand a burning mass measuring 1.5” X 1.5” and weighing ¼ of a gram.
  • Last 20 minutes before ignition.
  • Resist three cycles of a gas flame turned on and off.

Examples include untreated woods, particle board, and plywood. It also includes faster burning whole woods. Class C is not recommended on a commercial or residential roof.

WUI (Wilderness Urban Interface)

This set of codes refers to sections of civilization that border/intermingle with undeveloped wilderness. It focuses mainly on wildfires and damage prevention against wildfires. As such, WUI requires a roof assembly classification known as Class A. Class A roofing assemblies are defined as being effective against severe fire test exposure. This generally involves fire-resistant roofing materials and ember/flame-proof construction. 

https://climatesmartglaciercountry.org/2017/09/11/burning-issues-climate-change-and-forest-fire-severity-conflagration-or-a-bunch-of-hot-air/

https://www.readygallatin.com/wildfire-mitigation/

When building or remodeling, it is very important to have a thorough understanding of your environment as well as the specific needs to ensure your homes remain protected within your area.

For further information on fire ratings and WUI standards, please reach out to Cornerstone Management Services today. 

 


 

Written by: 

Alex Schaff — R&D Engineer 

Edited by: 

Paul Williamson — Director of Business Development

Cited:

https://alliedsvcs.com/is-your-commercial-roof-fireproof/#:~:text=Examples%20of%20common%20Class%20C,a%20commercial%20or%20residential%20roof.

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