The Riggors of Firestop Tests – T Rating Codes

Posted on 9/13/2018 7:17:32 AM By Sharron Halpert

Welcome back to our discussion.  We have been talking about the various ratings that firestop applications can provide. We have already discussed the L rating and we have moved on to the T rating.  During our last post, we talked about what the T rating is and why it is critical to the performance of your rated assemblies.  When we left, I promised to tell you where you can find this requirement in the codes.

I know you may not be chomping at the bit to talk about codes, but we will make this a practical discussion so it won’t be that bad.  Our office is in NJ so we deal with the 2015 IBC and, for the sake of this discussion, please know that the code citations are pulled from the 2015 IBC.

If you want to know what code is being used in your jurisdiction, other parts of the US or around the world this link will show you

If you want to source the full code section I reference, you can find an online version of the 2015IBC here

The information we will be referencing today will all be found in Chapter 7.

First let’s talk about T rating requirements in wall applications.  For this, I will just give you the code section and then we will talk about it:

CODE: 714.3.2 Membrane penetrations.  It says:  Where walls or partitions are required to have a fire-resistance rating, recessed fixtures shall be installed such that the required fire resistance will not be reduced.   Exceptions: 4. Membrane penetrations by boxes other than electrical boxes, provided such penetrating items and the annular space between the wall membrane and the box are protected by an approved membrane penetration firestop system installed as tested in accordance with ASTM E814 or UL 1479…shall have an F and T rating of not less than the required fire resistance rating of the wall penetrated and installed in accordance with their listing.

First, what is a membrane penetration? 

It is any application where the penetrating item does not go through both sides of the rated assembly.  In this case we are talking about walls, but it could be a floor penetration too – but right now let’s take this one thing at a time and stick with walls.

Some examples of a membrane penetration might be electrical boxes, and this code section goes in depth about electrical boxes. Exception 4 speaks to boxes other than electrical boxes so we will stick to that as well.  So, examples could be the shower diverter valve in a bathroom, the washer box in a laundry room, the water pipes that come up through the floor inside a wall and only poke through one side of the wall in a janitor’s closet.  Fire extinguisher cabinets and hose boxes are another example. It could be a time clock or an elevator call box in an office building.  It could be med gas boxes in a hospital or boxes behind commercial stoves in a kitchen facility.  There are heaps more, but this gives you an idea of what we are talking about.

Historically, many of these applications have been “five-sided” which means the drywall contractor would wrap the opening in drywall and be done with it. It is easy to see how someone who doesn’t understand how rated walls are tested and the common failure points of such tests, could think, “I’m using the same material that is used in the rated wall, so it will work.” The reality is that if you were to test what most five sided installations look like in the field, they would not just fail, but they would fail quickly.  If we want to focus just on the code, then the problem is, that with this new code requirement, the protection needs to be built with a material that is tested and listed. The reality is, five-siding a box with drywall won’t meet this requirement.

So if you can’t five side the boxes like they have done in the past, what do we do to protect them?  Simple – you need to find a tested and listed material and install it as instructed.  Here is an example of a solution for a utility controller cabinet:  When you look at this you will note that the F rating and the T rating are equal so this application fulfills this code requirement.

This solution works for a shower diverter box, even when they are installed back to back:

If you have an application where the membrane penetration is already installed in the wall and now you have to protect it, this detail might serve your purpose depending on the specifics of your application and if they match this tested assembly or can be modified to match:

Here is an example of a membrane penetration of a duct. If you look through this, you will see that the F rating equals the T rating which means that this detail can be used and can conform to this code requirement.  Can you say the same of the solutions being used on your project?

If you read the last blog post, you now understand what the T-rating is, the role it plays in testing any rated assembly, rated joint or through penetration; you also can see why it is critical to maintaining the expected level of life safety in a building.

Can you think of a way to help the construction industry achieve this goal?  If so, contact me and lets talk!  Join us next time when we talk about W rated applications.

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