Top Fire-Rated Assembly Questions and Answers

Feb 15, 2023 by Alan Zeedyk

OnBoard Newsletter | February 2023

Top Fire-Rated Assembly Questions & Answers

UL fire-rated assemblies are integral to every project you design. Yet, there seems to be some confusion about these assemblies. We receive many questions, including this one: “While choosing the appropriate UL designs for my project, can I make any adjustments to that assembly to fit my specific need better?”

To answer this specific question, changes to a UL fire-rated design are permitted, such as reducing the stud spacing or increasing the thickness of the gypsum board. But for details about modifying a specific UL fire-rated assembly before specifying, talk with an excellent resource, your construction design manager. And for more comprehensive information, check out National Gypsum's FAQ section.

Another question your peers often ask: “Is fire-taping the base layer necessary in multilayer assemblies?” The answer: No, you do not need to use joint treatment materials on base layers of multi-layer fire-rated assemblies.

What happens during the ASTM E119 Standard Methods for Fire Tests of Building Construction and Materials?

Per ASTM International Test Methods, the ASTM E119 test “evaluates the duration for which types of building elements contain a fire, retain their structural integrity, or exhibit both properties during a predetermined furnace test exposure.” There are four steps the assembly undergoes: preparation, burn, time/temperature curve and hose stream test. Watch the video below to see this test in action.


Top fire-rated assemblies in commercial construction

These are the most common fire-rated designs using gypsum board in commercial and multifamily construction. This includes a fire-rated horizontal ceiling membrane assembly – something else we often receive inquiries about.

Steel stud partition & horizontal ceiling membrane assemblies
V438 | 1-4-hour steel stud partitions
W419 | 1-4-hour shaftwall partitions
V488 | 1-2-hour steel stud chase walls
V497 | 1-2-hour steel stud assemblies constructed from one side
I504 | 1-hour horizontal ceiling membrane 

Wood floor-ceiling & roof-ceiling assemblies
M563 | 1-hour floor-ceiling on 2x10 joists
L558 | 1-hour floor-ceiling on wood trusses
M546 | 1-hour floor-ceiling on wood I-joists
M559 | 1-hour floor-ceiling on wood joists with 2 layers of type X
P533 | 1-hour roof-ceiling on wood trusses

For an in-depth look at more top fire-rated assembly questions your fellow architects ask and answers to those questions, check out this NGC Blog article!

Building Knowledge Together

Did you know we also offer a relevant AIA HSW continuing education course, "Understanding the UL Fire Resistance Directories" on-site or virtually? Schedule your next continuing education opportunity for your team now!

"Architects frequently ask me for alternate UL designs. A good percentage of these inquiries range from increasing the stud size to adding insulation to including plywood, and they are easily resolved with the allowed modifications outlined in the UL General Information for Fire-resistance Ratings. After sharing this information, many tell me that they were not aware of these published allowances. I encourage you to share these UL design guidelines with your staff to keep them updated about approved UL modifications."

Alan Zeedyk


Alan Zeedyk

Construction Design ManagerNational Gypsum Company

"With complex projects in today’s commercial construction, there is a need for as much technical information as possible. It helps to have a trusted advisor to learn where to find timely information and get the answers you need. NGC blog posts, FAQs and our AIA continuing education courses can be that trusted resource for you."

Frank Fuller


Frank Fuller

Construction Design ManagerNational Gypsum Company

Resource Spotlight

Your Go-To Guides for Fire-Rated Assemblies

The PURPLE Book® - The leading resource on fire-rated assemblies in commercial construction.

The Wood Book™ -  A comprehensive guide for fire-rated assemblies in wood-frame construction.

Project Profile | Mark & Paul Hurd Welcome Center at Baylor University


Owner: Baylor University | Waco, TX

Architect: POPULOUS | Kansas City, MO

General Contractor: Vaughn Construction | Dallas, TX

Subcontractor: Denman Building Products | Amarillo, TX

Distributor: Gypsum Management & Supply (GMS) | Waco, TX

Baylor University’s new $60-million, 120,000-square-foot Mark & Paula Hurd Welcome Center will create a dynamic first impression for prospective students, families, alumni and visitors.

Read more about this project and the products used.

Expert Connection

From expertise on building products in fire- and sound-rated assemblies to specifying the best products for your next project, we have a construction design manager available to provide architectural design assistance every step of the way. We are here to help you design and build better. Connect now!

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