Fire Ratings for Roofs: Class A and Product vs. Assembly

What are fire ratings, and how does testing differ when it comes to assemblies vs. products? In this article, we discuss the differences and more.

Around 70,000 wildfires occur in the United States every year, threatening the safety of residents and businesses. Fires are unpredictable, and as we’ve seen in recent years, they can leave whole areas devastated.

Homeowners and building owners can only do so much to guard themselves against the harsh effects of nature, whether that be wildfires, hurricanes, or hailstorms. But certain variables can be controlled — such as roofing materials — to promote safety during extreme weather events.

Sheffield Metals International (SMI) has spent decades building relationships with business owners in the metal roofing industry. While we are a leading supplier of metal coils and sheets, we also commit to helping others build their businesses and learn about the technical aspects of metal roofing.

In this article, we’ll discuss fire ratings for metal roofs, including:

  • What are fire ratings?
  • What is a Class A fire rating?
  • Differences between Class A-rated products and assemblies
  • Strategies for getting a Class A fire rating for an assembly

By the time you’re done reading, you’ll have a better idea of what fire ratings are and how they may impact your next metal roofing project.

What Are Fire Ratings for Roofs?

Fire ratings are given to roof products or assemblies after they’ve passed the proper testing. The ratings, which are split into three groups — A, B, and C — indicate how flame-resistant the roof is. These ratings offer an easy sign for buyers who are looking for a specific fire resistance for their roof. They also help ensure builders and architects are following local building codes.

So how do you get a fire rating?

To get a rating, the roof product or assembly must go through three tests, each one forcing the material through a different type of vulnerability:

  • Spread of Flame Test: The roof must withstand a maximum, measured flame spread.
  • Intermittent Flame Test: Measuring a flame cycling on and off a roof sample.  
  • Burning Brand Test: A measured burning brand is applied to the material.

A fire rating – A, B, or C – will be given to the roof sample based on its performance during these three tests.

If you’re working on a project, whether you’re the architect putting together the design or a contractor starting a new project, it’s essential to check your local jurisdictions and find out what your specific area requires regarding fire ratings. Every area will be different, so be sure you’re tailoring your project to those specific regional needs and building them into your initial project plans.

In regions where wildfires are common, such as the Western U.S., it may make sense or even be required by local codes to have a Class A fire rating for a roof.  

What Is a Class A Fire Rating for a Roof?

A Class A fire rating is the best fire rating you can achieve for a roof. Many companies use the UL 790 to test to achieve Class A fire ratings for roofing products. Class A ratings are ideal and, in some cases, required for various applications, including:

  • Commercial buildings: Standards for commercial structures are often higher because they are operating businesses. Many will require weathertight warranties, and Class A fire ratings are often attained for best safety practices.
  • Emergency facilities: Buildings that offer emergency services, such as hospitals, need premium durability, especially in times of crisis.
  • Areas prone to wildfire: Wildfires continue to grow prevalent in the U.S. Those in affected areas will benefit from choosing a Class A fire rated roofing system.

Roofs that achieve a Class A fire rating must be able to stand up against severe fire exposure. Other factors will be in play to achieve any fire rating, such as whether your rating is for a product or an assembly.

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How Do Class A Rated Assemblies and Class A Rated Products Differ?

Metal roofs are often favored over other roofing materials when it comes to fires. Since steel is a non-combustible material, it’s easy to get a Class A rating for a metal roof panel, as it won’t burn unless it reaches an extremely high temperature.  

However, even if you have a Class A-rated product, such as metal panels, it doesn’t mean that everything in the assembly will match that rating.

An assembly is your entire roofing system, from the deck up, including the panels you have and what you’re attaching them to. It is much more challenging to achieve a Class A rating for an entire roofing assembly than for the product, as the assembly is often comprised of varying materials, such as wood.

If you have an assembly with metal decking and panels, getting a Class A rating will be much easier, as the materials are non-combustible. But if you’re dealing with combustible materials in the assembly, you must take additional steps to protect those materials and achieve a Class A rating.

Each metal roof manufacturer may or may not have a fire-rated assembly. However, if you are required to build one, you must follow the manufacturer’s procedures for doing so. Just as a combustible product could be in a fire-rated assembly, you could have a series of non-combustibles in an assembly. However, if it is not installed per the manufacturer’s specifications, it would not qualify as a fire-rated assembly. 

If an assembly has combustible materials, it doesn’t mean it’s barred from achieving a Class A fire rating. It just means that additional materials will be required to protect those combustible materials. There are two popular ways to do this. 


DensDeck is made with a gypsum core and fiberglass mat facers. The gypsum core also contains 21% crystallized water, which is released when exposed to fire. Installers place the DensDeck on top of the combustible material in the assembly and then build the rest of the assembly over it. Make sure you’re using the right thickness of DensDeck as directed by the Class A fire rating.

GAF VersaShield

The GAF VersaShield is a fire-rated product. Like underlayment, it comes in a roll and can easily be unfurled onto a roof. One or two layers of this product can bring your assembly up to a Class A rating, depending on the type of materials you’re using. The VersaShield is light and easy to maneuver for installers, making it a popular choice when it comes to trying to attain the Class A fire rating.

Looking for More Information on Fire Ratings for Metal Roofs?

Fire ratings are an important aspect of any roofing system. Although metal roofs are often seen as an excellent choice for fire resistance, it’s essential to consider the entire assembly and the materials you’re using for your project. Feel free to check our additional content on this topic, including our video on whether metal roofs are fireproof.

While content like this can be helpful, you may be looking to speak directly with an expert about fire ratings and how they relate to your unique project. Sheffield Metals has a Technical Department ready to assist with any questions you may have. Feel free to reach out today.

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