Perimeter Containment- Firestop Joints. Let’s Find a Better Solution -part 1 of 2-

Posted on 1/30/2018 10:49:03 AM By Sharron Halpert

A challenge for the creative problem solvers

In our blog on 12/7 we had a discussion about firestopping on rated joints, but we did not talk specifically about the different types. Did you know that the building code requires the rating of the floor to remain continuous up to or through the exterior façade of the building.  If the façade sits ON the floor, clearly the code requirement is met.  However, when the façade hangs off the edge of the floor, this slot can be as small as ½” or up to several feet. In this blog and the next we will pose a challenge to manufacturers to combine existing technologies in other industries in order to create a whole new product that might provide a better solution and a faster installation.  Are you interested in creating something the market has never seen AND making buildings safer?  If so, read on my friends!

(This is an example of what one type of perimeter containment gap looks like before installation.)

If you have read much on the Grenfell Tower fire in London, you know that, on top of the concerns about the combustible exterior facades, there is also the potential that there was likely nothing in that slot that we mentioned.  If this were the case that means there was nothing that would stop the fire and smoke from spreading from one floor to the next, inside the building.   The building was not protected with a fire sprinkler system and while this would have likely reduced the tragic impact considerably, it would not have stopped the migration of smoke and toxic gasses that contain deadly elements such as hydrochloric acid, hydrogen-cyanide and carbon monoxide.

So, today I want to challenge you to come up with some crazy solutions for this slot and I have a few ideas for you to play with. First, I will explain the way these slots are currently protected. Then, we will address the problems with this as a solution.  Then in the next blog post, I will give you a few ideas to toy with and leave you to be creative.

A typical installation will require mineral wool stuffed in the slot and a firestop spray over the top of the mineral wool.

Here are some issues with the way installers do this today.  First, the mineral wool orientation is critical to the performance of the installation.  Have a look at the mineral wool. 

9-mineral wool.1
(fibers run up and down)

9-mineral wool.2
(fibers run left to right)

On the top picture the fibers run up and down, on the bottom picture they run left to right. The material needs to be running to the fibers are parallel with the gap. If the mineral wool is installed with the fibers perpendicular to the slot, the fibers will be crushed little by little as the joint experiences movement.  Over time, there is risk that the material will not remain in place.  When the fibers are running parallel to the movement of this slot, the material can compress and extend as the façade moves with the temperature change from day to night.

9- waffel marks
(If you see these waffle marks through the spray, you know the installation is wrong)

If you see the fibers running from the floor slab to the exterior façade, again you know the installation is wrong.  In this case you can see slight waffle marks that are a result of the manufacturing process. This is an improper installation as well.

The next potential problem with a typical installation is that some details require up to 50% compression of the mineral wool.  This proves to be a challenge not only in the physical installation, but also with the comprehension of exactly how to figure this. If you have a 4” joint, a lot of contractors look at the math this way.  50% of 4” is 2 and 4”+2” is 6.  That means that 6” of mineral wool is going to give a 50% compression.  The problem is, the math is backwards and this provides only 33% compression.  If you have 8” of mineral wool and you compress it 50% you have 4” of compressed mineral wool that should be placed in a 4” joint.  When it is explained this way, the math sounds easy enough, but try to install this in the field and you will see the next challenge.  Many installers unknowingly cheat this.  Some do it flagrantly.

The final problem comes with the spray that should go over the top. 

Most details require 1/8” wet or 1/16” dry. As you can see in the photo below, being able to see the mineral wool fibers through the sealant it is easy to guess that the required sealant depth has not been achieved in this installation.

(When you see an installation like this, you can't say the depth is correct)

In addition, the spray typically needs to overlap the concrete floor AND the exterior facade a minimum ½”.

9-12 lap
(As you can see there is plenty of room for worker error with both of the steps in this installation)

This next photo shows an example of a proper installation, the mineral wool is installed flat, increasing the chance of achieving consistent sealant depth, the overlap onto the concrete and onto the insulation looks to be good as does the sealant depth.  Of course this is not a typical field installation.

9- main picture

Now that you understand the current installations, try to mull over some ways to improve upon these problems. Maybe find a better insulation, or a better means of sealing the slot, or just a better installation method.  Let’s find a way to make this installation easier, or rather more difficult to do incorrectly.  In our next post I will give you a few ideas of my own to consider and then we shall see what you can do.

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