Roof Fire Ratings 101

Over the past twelve years or so, an increase in structural fires nationwide has proven that roof fire ratings are more critical than ever for building safety. According to FEMA, financial losses from fires were up 90.6 percent between 2009-2018 (over $25 billion in 2018 alone), and fatalities were up 20.5 percent. For non-residential buildings, the numbers were even worse, with 26 percent more fires and 30 percent more deaths.

If nothing else, these numbers underscore the importance of implementing building designs and materials that can resist fire – or at least minimize the damage caused by them. How a building stands up to fire exposure can significantly impact the amount of loss incurred.

The Importance of Roof Design in Fire Safety

The right roof design, and the right choice of roofing materials, are critical to a building’s fire safety for at least two important reasons:

  • A roof is the most vulnerable part of a building. The roof is the first line of exposure to all the elements, including rain, wind, lightning strikes, or floating embers from a nearby fire.
  • A roof can restrict a fire’s oxygen intake. Fires need oxygen to survive. If an internal fire breaks through the roof, it gets a fresh supply of oxygen to amplify the damage to the building itself.

Taking these factors into account, a fire-resistant roof is a key line of defense for the entire structure because of the potential to minimize damage from fires threatening the building from both without and within.

Why Roof Fire Ratings?

To facilitate the process of encouraging greater fire safety in building construction, the building industry has adopted a rating system for categorizing the fire resistance of various roof coverings and materials. These roof fire ratings provide builders and building stakeholders with the following advantages:

  • Facilitates better fire code compliance. Roof fire ratings make it easier to meet fire safety recommendations set out by building codes of practice.
  • Establishes a standardized system of measure. By assigning a roof fire rating to known roof covers and brands, no one is left wondering whether or not that roof cover is safe.

How are Roof Covers Rated?

Fire ratings on various roof coverings are determined using a standard fire test which evaluates the roof’s performance during fire exposure. This test looks at the following three criteria to establish a rating:

  1. Flame penetration. How easily or quickly do flames penetrate through the roof into the attic?
  2. Flame spread. How easily or quickly do flames spread across the roof surface?
  3. Ember generation. How easily or quickly does the roof covering lose integrity, dislodging or breaking and releasing embers for further fire spread?

The A-Cs of Roof Fire Ratings

Using the standard fire test results, roof coverings are given a Roof Fire Rating of Class A, Class B, or Class C, depending on performance. Let’s take a closer look at these ratings.

Class A Rating

Class A is the highest roof fire rating possible for a roof covering. It’s a desirable rating for all roofs, but it’s considered even more essential for buildings in locations where wildfires are more common. To achieve a Class A rating, the roof must pass the following criteria during testing:

  • Have a flame spread of no more than six feet.
  • Be exposed to fire for 2-4 hours before igniting.
  • Support a burning brand of 12″ x 12″ and 4.4 lbs (2,000 g) without losing integrity.
  • Resist a gas flame turning on and off for at least 15 cycles.

Examples of Class A-rated materials include slate, concrete and clay tiles, and asphalt/glass fiber composition shingles. Certain roofing materials more prone to fire may also obtain a Class A rating when used in combination with other fire-resistant materials (for example, when treated with fire retardants, or used with a fire-resistant underlayment).

Class B Rating

A roof covering achieves a Class B rating when it affords moderate fire protection but not as effectively as Class A. Most shakes and shingles pressure-treated with fire retardants fall under Class B.

To receive a Class B rating, the roof covering must:

  • Have a flame spread of no more than eight feet.
  • Be exposed to fire for at least one hour before igniting.
  • Support a burning brand of 6″ x 6″ and 1.1 lbs (500 g) without losing integrity.
  • Resist a gas flame turning on and off for at least eight cycles.

Class C Roofing

Class C is the lowest roof fire rating, affording only minimal fire protection. Class C roofs meet the following criteria:

  • Have a flame spread of no more than 13 feet.
  • Be exposed to fire for at least 20 minutes before igniting.
  • Support a burning brand of 1.5″ x 1.5″ and .5 grams without losing integrity.
  • Resist a gas flame turning on and off for at least three cycles.

The most common examples of Class C roofing include untreated plywood, particle board, wood shakes, and shingles.

What About Unrated Roof Covers?

Simply put, beware of unrated roof coverings. When a roof is unrated, it does not mean untested; it means it could not even meet a Class C rating. Unrated roof coverings offer little to no fire protection, neither do they meet the minimum standards of most local building codes. Fire exposure on an unrated roof is a recipe for disaster.

Why RoofSource?

As a building products manufacturer representative company partnered with some of the industry’s most reputable brands, RoofSource works with top professionals and product manufacturers keenly aware of the need for fire safety in their roofing products systems.

Our scope of work and specifications for each project incorporate the highest roof fire ratings allowable, based on budget requirements and building code standards. Our onsite presence with each project ensures accountability regarding the proper installation of these materials for maximum fire safety.

If you’re concerned that your building’s roof covering doesn’t provide enough fire protection or poses a safety risk, RoofSource can provide a comprehensive assessment and make recommendations to improve your roof’s fire rating. Contact us today to learn more.