Why Firestop in Shaft Walls is Often Improperly Installed (part 1) 

If you have been following this blog you know how I love to do a series of posts on a topic. If you have been to one of my classes, you know how often I segue to other topics. This one is going to be a combination of these habits and we will come full circle, eventually (there is A LOT to share with you all), especially as we discuss Why Firestop in Shaft Walls is Often Improperly Installed.

This series will focus exclusively on shaft walls. Our hope is that this series gives you new tricks for reviewing firestop submittals early in a project. You’ll also learn what to look for during construction site walks. This series targets firestop installers, inspectors, superintendents, building owners, architects, and GCs. It’s for anyone who needs to assess the red stuff and determine its correctness, addressing Why Firestop in Shaft Walls is Often Improperly Installed.

Let’s start with looking at the different types of shafts and what purpose they serve from a code perspective. 

WHY DO WE HAVE SHAFTS? 
The building code basically says you have to firestop any hole in the floor, or you have to stick the hole in a shaft. You really need some holes in the floor, like those created for elevators or stairs. There are other holes that you could firestop, but it’s easier to just protect the hole with a shaft, one such example could be a mechanical shaft. 

Generally, when you build a shaft, it will have the same rating as the floors that it runs through, so in most concrete projects we are talking about a 2-hour shaft. 

The 2015 IBC section 713 is all about shaft enclosures if you want some light reading. You can find copies on line these days. 

WHAT ARE SHAFTS MADE OF? 
Here are three basic types of shaft wall assemblies you will see: concrete, block and gypsum. We will discuss all three here and remind you of some common problems with each type. Remember, one shaft could potentially consist of all three materials.

Concrete shaft walls are the easiest ones to get right. One reason is the fewer rated joints needing firestop. Also, punching a hole in a solid concrete wall isn’t easy, so people usually plan or avoid penetrations. Still, you may have penetrations for electrical, sprinkler or ductwork. Please remember that firestop on walls needs to be on BOTH sides of the wall. Let’s think about this for a moment and talk about the problem this creates for installers. If you only have access to one side of the wall, how do you propose protecting both sides of the wall? Hang on, we will get to that in a bit. 

Block walls are not so bad to firestop either. Except in stairwells, where stair runners often block the head of wall joints that require firestopping. Improperly firestopping the joint leaves the area vulnerable to the passage of fire, smoke, and toxic gas. Keep in mind that the stairs are typically your means of egress in an emergency because you won’t be able to use the elevators. This means that getting the fire protection right in these areas is critical to the life safety of a building. 

Gypsum shaft walls create the most problems we’ve seen, from a shaft perspective at least. It starts with the basic construction. Does the contractor know that they need to stagger the corners of the wall and not run both layers in the same plane? A typical 2-hour gypsum shaft wall consists of a 1-inch shaft liner and two layers of Type X drywall. The seams of these two layers of type X should not line up anywhere, including at the corners. Since drywall shrinks during a fire, any seams that line up create an extra risk. The required overlaps allow for the shrinkage without the risk. Corners are critical because too often the drywaller lines up the two layers rather than staggering them making a straight line seam rather than a stair stepped seam. 

Remember, you must firestop the head of wall joint, regardless of the shaft type you build. Also, remember to firestop BOTH sides of the wall. If you have an elevator shaft, then someone will likely have to ride on the top of the car to firestop the joints and penetrations inside the shaft. The same is true for a mechanical shaft except access will be… shall we say… limited, if not impossible. 

Next up, let’s look at the penetrations through these shaft walls. They, too, need to be firestopped from both sides. If access is impossible there are a handful of alternate solutions. Many of these will require an Engineering Judgment that should be created following the IFC guidelines found here. 

In our next post we will go over what to look for when you are reviewing the firestop submittals specific to shaft walls.