ARE FIRE-RATED JOIST HANGERS WORTH THE COST? A LOOK AT FIREWALL FRAMING
When it comes to framing a building and meeting fire safety codes, contractors and builders have a few different options. You can use traditional methods, like resting joists directly on top of a wall with multiple layers of blocking, or you can invest in specialized hardware like top flange fire-rated joist hangers. But are these expensive gadgets actually worth the cost, or are they just driving up the budget of your build? Let's take a closer look at both methods.
TRADITIONAL FIREWALL CONSTRUCTION METHODS
Before spending money on specialized hangers, it is important to understand that you can build a highly effective firewall using standard construction lumber and drywall. A common method involves resting the joist on top of the wall and using blocking to create your fire rating.
As a general rule of thumb, a standard one and a half inch piece of construction lumber provides about a one-hour burn-through rating.
One block equals a one-hour rating.
Two blocks (double blocking) equals a two-hour rating.
Three blocks (triple blocking) equals a three-hour rating.
Additionally, you can notch the drywall around the joist to increase the firewall's effectiveness. One piece of drywall typically offers a one-hour rating, while two pieces offer a two-hour rating. While you should always consult with an engineer and check your local city building codes for exact approvals, this traditional method is a proven way to create a firewall without the need for expensive hardware.
THE PROS AND CONS OF TOP FLANGE FIRE-RATED HANGERS
For those who prefer specialized hardware, top flange firewall hangers are an alternative. These hangers are attached at the top, and the joists are fastened to the hangers with nails at the bottom.
One of the major selling points of these hangers is convenience. They are designed to allow drywall to slip behind the joist, meaning the drywall can be installed much easier after the building's structural framing is complete. In traditional framing, installing drywall around joists can slow the job down significantly, so these hangers do offer a distinct time-saving advantage.
However, that time savings comes at a massive financial cost. These specialized hangers can cost around forty-seven dollars each. For larger beams or large open web joists, a single hanger could cost anywhere from one hundred to two hundred dollars. When you multiply that by the number of joists in an entire building, the cost of hardware alone can blow your construction budget completely out of the ballpark.
DEBUNKING THE STRUCTURAL SAFETY CLAIMS
In addition to the high cost, some of the structural safety claims surrounding these hangers are questionable. Some sources suggest that if a joist is on fire and begins to sag or burn through in the center, it will simply fall out of the hanger. The claim is that this reduces or eliminates the chance of the falling joist pulling the entire wall down with it.
From a practical construction standpoint, this theory has flaws. For the joist to simply fall out, it would have to perfectly separate from the bottom nail connections. Furthermore, the floor sheathing would have to completely burn through first, because the top of the joist is securely attached to the floor sheathing, which is in turn attached to the wall. The idea that the joist will seamlessly drop away without impacting the wall is highly unlikely in a real-world fire scenario.
CONCLUSION
While top flange fire-rated hangers offer a real benefit when it comes to the speed of drywall installation, it is incredibly difficult to justify their exorbitant price tag. Designing a building with these hangers might make sense for someone who has an unlimited budget or is strictly following a specific recommendation, but for most builders, it simply is not cost-effective. There are other traditional blocking and drywall methods that, while perhaps slightly less efficient during the drywall phase, are significantly cheaper and just as effective at creating a safe, code-compliant firewall.
