Design tips for corners and intersections of fire-rated walls and partitions
Best practices for corner details where two rated assemblies meet
The National Gypsum Construction Services department frequently receives questions via the 1-800-NATIONAL hotline regarding the proper way to detail corners and intersections of fire-rated walls and partitions.
While wall and partitions are tested in accordance with ASTM E119, there is no standard test method for measuring the fire resistance of corners or intersections, and they are not addressed in assembly directories available from UL Solutions, the global product testing and certification company, or the Gypsum Association.
Why aren’t corners and intersections tested? The furnace used for testing assemblies has only one side open and is not L-shaped, so it cannot accommodate corners.
Resource alert: Learn how the ASTM E119 test is conducted and watch a video of the test being conducted.
What are the top considerations for corner details and intersections?
The PURPLE Book® and The Wood Book™, both available from National Gypsum, provide simple and clear guidance on best practices for corner details. Since these details cannot be tested, they are merely recommendations based on the following principles:
- Continuity of the gypsum board
- Support for all gypsum board edges
- Wall priorities at intersections with dissimilar fire ratings
Maintaining continuity of the gypsum board membrane
Maintaining the continuity of the gypsum board membranes around the corner is the most important consideration to ensure adequate fire protection. See details below for one- and two-hour rated wood stud walls.
Ensuring the continuity of the gypsum is straightforward in symmetric assemblies, but it can get tricky with asymmetric walls. See the examples below for inside and outside shaftwall corners. Notice in the second detail, the additional piece of shaftliner panel fastened to the web of the J-track to maintain the continuity of the shaftliner around the corner.
As with corners, where one wall abuts another at a “T” intersection, the gypsum board membranes simply wrap the framing as illustrated in the diagrams below, provided the walls have the same fire-resistance rating.
Support for all gypsum board edges
Additional framing may be required to support all the gypsum board edges in multilayer systems.
Wall priorities at intersections with dissimilar ratings
Where walls of dissimilar fire ratings form T intersections, the continuity of the higher priority wall must be preserved. In the examples below, the two-hour assemblies are continuous, while the one-hour assembly abuts into the side of the higher priority wall.
How do corners differ from the middle of a wall?
“Failures typically occur somewhere in the middle of the wall and often at a horizontal joint," says Sam Halverson, construction services manager with the 1-800-NATIONAL® Construction Services Team. "The additional studs required to frame the corner provide more stability."
- Gypsum board joints: Unlike horizontal joints that can open during a fire, corners are vertical joints which are backed by framing that inhibits the passage of fire and heat.
- Additional studs: To support all the gypsum board edges, corners require additional framing members adding more material through which a fire must burn.
- Deflection: When tested in accordance with E119, Standard Test Methods for Fire Tests of Building Construction and Materials, walls undergo lateral deflection. The middle of the wall bows inward toward the fire, but not at the edges where it is attached to the test frame. The adjacent wall in a corner would help prevent this deflection to occur during a fire event.
“Because corners cannot be tested, there is no way to prove they are safer," says Halverson, "but if I'm ever trapped in a burning building, you'll find me standing in the corner."
Technical guides from National Gypsum
Download The PURPLE Book
and The Wood Book
today as helpful resources for common design and construction challenges. Need to talk through a solution? The 1-800-NATIONAL Construction Services team is ready to help.
