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).
This is going to be a series dedicated just to shaft walls. Our hope is that after this series you will have a few new tricks up your sleeve when it comes to reviewing firestop submittals in the early stages of a project and knowing better what to look for when you are walking a project during construction. This series is for firestop installers, inspectors, superintendents of any trade, building owners, architects or GC…anyone who ever has to look at that red stuff and wonder if it’s right or not.
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. There are some holes in the floor that you really need, such as the hole that is created for an elevator 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. Bear in mind one shaft could potentially be made of all three materials.
Concrete shaft walls are the easiest ones to get right. One reason is because there are fewer rated joints that need to be firestopped. Also, it’s not easy to punch a hole in a solid concrete wall, so penetrations are typically planned for or avoided. 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. That is except when you are talking about a stairwell, because then, the head of wall joint that requires firestop is often blocked by the stair runners. When the joint is not firestopped properly, this can leave the area vulnerable for 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 is going to be made with 1” shaft liner and 2 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, regardless of what type of shaft you build, the head of wall joint needs to be firestopped. Remember also that it needs to be firestopped on 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.