Achieving a Class A Fire-Rated Roof Assembly


Tackling Common Low-Slope Challenges

I have over a decade of experience helping roofing professionals with low-slope roofing installations and inspections. As I travel the United States delivering CertainTeed’s popular Flintlastic® SA Commercial Roofing Installation training courses, I take note of our customers’ questions, challenges, and misconceptions. 

You may have seen my video series, Joe Knows, featuring tips and tricks for installing low-slope roofing. Now I’m also sharing guidance and insight here, with Joe’s Journal, a blog series where I address some of your most common questions.

Look Beyond the Cap Sheet

When it comes to commercial roofing, achieving a Class A fire-rated assembly isn’t as easy as selecting a fire-rated cap sheet. Yes, you’ll need that fire-rated cap sheet, but that on its own won’t get you a UL Class A rating.  

Why? Because fire rating is determined by testing of the entire roofing assembly. 

Fear not; achieving Class A with a rolled roofing system is simple if you do three things before installation: 

  1. Know the deck type and slope. 
  1. Know the insulation composition (if applicable), base sheet, interply (if applicable), and cap sheet, as well as their installation methods. 
  1. Check your proposed assembly against the current UL Class A fire-rated listing—and adjust if needed. 

It’s important to take these steps before ordering materials, as UL assemblies are not always flexible. You don’t want to discover half-way through installation that you aren’t using the right products and need to change your system. 

Planning Your Class A Assembly

Here’s an example of how you might plan a Class A assembly. Let’s say you are installing on a combustible deck with an incline of 2. You’ve decided to use Flintlastic GTA-FR for your cap sheet. How do you determine the rest of your assembly? 

The UL guidelines—which you can access here or by contacting your Territory Manager—offer two possible routes to a Class A rating for a system with that deck, incline, and cap sheet: 

59. Deck: C-15/32 Incline:
  • Base Ply: Type G2 or alternate (see preamble table). 
  • Ply Sheet: Flintlastic Ultra Glass SA, self-adhered. 
  • Membrane: Flintlastic GTA-FR, heat fused. 
67. Deck: C-15/32 Incline:
  • Barrier Board: Minimum 1/4-in. thick United States Gypsum Co. SECUROCK® Gypsum-Fiber Roof Board (Type FRX-G), mechanically fastened. 
  • Ply Sheet: Flintlastic STA or Flintlastic APP Base T, heat fused. 
  • Cap Sheet: Flintlastic GTA-FR, heat fused. 

Now you can decide if either of these assemblies work for your project, or if you need to choose a different cap sheet in order to achieve a Class A assembly that does. 

Remember: While it is sometimes possible to deviate from the UL-rated assemblies, don’t assume that you can. Get confirmation before you decide to use different components or application methods. 

Ask Us What You Need to Achieve Class A

As you begin to plan your next project, your CertainTeed Territory Manager is here to help you tackle it with confidence and meet all UL Class A fire rating requirements. When you reach out, we’ll ask you the following questions about your assembly: 

  • Deck type 
  • Slope 
  • Cap sheet 
  • Insulation 
  • Warranty term 
  • Application method 

Armed with this information, we can then help guide you to the best UL Class A fire-rated assembly for your project. 

Have a Question for Joe?

If you have any questions, you can submit them via this form or leave a comment below. For additional information on CertainTeed products and installation, please visit

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About Joe Thompson

A key member of the CertainTeed Commercial Roofing Technical Services team, Joe Thompson has been assisting customers with low-slope roofing installations and inspections for nearly two decades. Not one to sit on his hard hat, he travels throughout the United States serving as lead instructor for CertainTeed’s popular Flintlastic SA commercial roofing installer-training courses. An IIBEC member in good standing, Joe has attended so many roofing educational courses that he has lost count.

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