Fire Resistance

How to build fire-rated wall assemblies from one side

Dec 6, 2023

Asymmetric wall assemblies from National Gypsum are designed to provide fire ratings where access is limited

Retrofits and renovations can be full of surprises. Whether you’re upfitting a shopping center dentist office into a restaurant or renovating an old mill building into a live/work/play destination, one of the most common challenges is how to design a fire-rated assembly in a wall that is accessible from only one side.

National Gypsum Company’s 1-800-NATIONAL® Construction Services team created and tested two UL fire-rated assembly designs for these exact situations, providing a versatile solution for practically any circumstance.

What are unbalanced or asymmetric wall assemblies?

Asymmetric, unbalanced or one-sided wall assemblies are fire-rated partitions with unequal layers of gypsum board on each side. They are designed to be constructed from one side while providing fire protection from both sides of the partition.

Asymmetric or unbalanced wall assemblies are ideally suited for:

  • Retrofit projects where a new fire-rated wall abuts an existing wall
  • Walls with recessed fixtures such as fire extinguisher cabinets, lights, or toilet room accessories.
  • Duct enclosures
  • Occupancy separations where a neighboring space needs to upgrade its fire rating

Let’s dive into the occupancy separation example since it’s one of the most common asymmetric wall assembly situations architects encounter — often in shopping centers where the retail mix varies drastically. For example, a printing and shipping shop shares a wall with an accountant’s office. Due to their business occupancy classification, the building code requires both to have 1-hour fire-rated walls. If the accountant’s office closes and a restaurant moves into that space, the occupancy changes to mercantile, which the building code requires to have 2-hour fire-rated walls. Since the printing and shipping shop can’t close to provide access to the new restaurant to upgrade the wall’s fire rating, the restaurant needs an asymmetric wall assembly to achieve the 2-hour fire rating.

How do you build fire-rated wall assemblies from one side to meet 1-hour and 2-hour fire ratings?

The National Gypsum 1-800-NATIONAL Construction Services team created two UL fire-rated assembly designs to solve the problem of one-sided fire-rated wall construction. Both have been tested from each side according to the ASTM E119 Standard Test Methods for Fire Test of Building Construction and Materials.

UL design V449 is ideal for occupancy separations and exterior walls that require a 2-hour fire rating.

UL design V449 takes an existing 1-hour fire-rated wall that has one layer of ⅝" Type X gypsum board on each side and converts it to a 2-hour fire-rated wall assembly constructed from one side by adding two more layers of ⅝" Type X gypsum board to just one side. In addition to being a simple solution for occupancy separations, it can also be used for exterior walls that require a 2-hour fire rating. Download a copy of V449 here or visit on the UL product IQ website.

Photo credit: 1-800-NATIONAL

UL design V497 provides options to construct 1-hour and 2-hour fire-rated wall assemblies from one side.

  • 1-hour fire-rated wall: Apply two layers of ⅝" Type X gypsum secured with a layer of setting-type joint compound between them. This design saves space but is more labor intensive. (Reference page 14 in The PURPLE Book®.)
  • 1-hour fire-rated wall: Apply three layers of ⅝" Type X gypsum board on one side.
  • 2-hour fire-rated wall: Apply four layers of ⅝" Type X gypsum board to one side.

The details below show options for building UL design V497. Download a copy of V497 or visit the UL product IQ website.

Photo credit: 1-800-NATIONAL

Gold Bond Fire-Shield Gypsum Board can be used in asymmetric wall assemblies.

Provided by National Gypsum through its manufacturing affiliate company Gold Bond Building Products, LLC, Gold Bond® Fire-Shield® Gypsum Board offers multiple benefits, including:

  • A fire-resistant Type X core
  • GridMarX® guide marks printed on the board
  • Tapered or square long edges
  • Face paper folded around the long edges to reinforce and protect the gypsum core

If the wall assembly is in a shower room or a corridor, consider using the following products as the outer gypsum board layer.

Technical support when you have a problem to solve

Whether it’s downloading a submittal from the Design & Resource Center, checking an order with the Customer Service Center or getting design assistance from a construction design manager, National Gypsum’s Excellence Across the Board® program provides industry-leading technical support and customer service. Reach out to 1-800-NATIONAL Construction Services with your technical questions today!