W Ratings Continued – Usefulness, Testing, Limitations

Posted on 1/28/2019 11:11:00 AM By Sharron Halpert

Our last post talked about how W ratings for firestop floor penetrations came about, how they are tested and we talked a little bit about what they can and can’t be expected to do.

Today, I am going to tell you a few stories of things I have seen in the field that supports the idea of using W rated firestop in spite of the apparent weaknesses from a testing perspective. First however let me explain a little bit more.

Silicone firestop materials are the most common material used for achieving  W-rating, but some manufacturers are testing new materials that are still able to achieve the W rating without the use of silicone materials.

One of the benefits of silicone is that some of it can be self-leveling. This can be an advantage over traditional materials. Traditional materials need to be troweled into place to ensure a seal between both the penetrating item as well as the floor the penetrations are running through.  Self-leveling materials can be an advantage because they can be installed without the necessary troweling. A good installer can actually save enough money to more than defer the cost of the more expensive silicone material.

There have been cases where the use of a self-leveling silicone firestop sealant in applications that are not considered capable of passing a complete W rating test, have been able to successfully prevent the movement of water.  Here is one such story.

We had a firestop installer who used self-leveling silicone firestop sealant for the following applications. All of which were inside a wall cavity:

  • Copper pipe with AB/PVC insulation (black foam rubber)
  • 1.5” hole in the concrete floor with two to three MC cables
  • Bare metal pipes

After construction was completed, a drywall screw was found to have punctured a copper pipe.  When the pipe leaked, the floor penetrations were sealed well enough that the wall cavity completely filled with water. Water was rushing out the holes in the wall where the electrical outlets were located. Once the water was turned off and the team began to clean everything up, they found that the water inside the wall was above the six-foot mark. They used a thermal imaging camera to look for cold spots inside the walls on the floor below. This might indicate the presence of water. When they went to the floor below the only areas where there were cold spots, where water came through, were at a mechanical shaft and down the stairs.

The firestop around the MC cables would not have been able to pass the W rating, with a traditional installation because the cables would be required to be tightly bundled, creating interstitial space between the cables that would allow water to pass. These installations were successful in preventing water movement in this case. The critical element was the fact that the installing team separated the three MC cables in the opening and ensured that mineral wool was between each of them and that the silicone sealant separated each of the individual cable segments. This attention to detail by the installers was critical to the unexpected success. This reduced the water damage and, when a good installer uses a self-leveling silicone, they can typically complete the installations faster, but that is a story for another time.

For now, let’s recap what we have covered in the last two blogs.

  • W rating firestop can be a critical element to reduce unwanted water movement inside your building during construction as well as once the building is occupied.
  • These materials are often (though not always) silicone based
  • W-rated firestop installations are not likely available for all floor penetration types. The requirement should be used only when fully understood, lest it create a whole different set of problems. A few examples given might be insulated pipes, cables and other more complex installations that would require alternate means in order to maintain this W-rating.

Now you should understand the reason W rated applications are useful and you should also understand their limitations.   If you have any questions, feel free to reach out to us or your favorite firestop manufacturer or specialty firestop installer for more information on how you can achieve a W rating on your next project.

Please note that W-ratings are not a code requirement, but once they are written into your project specifications they do become a contractual obligation.

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