What is a W-Rating?

Resisting Water Passage 

The W-rating refers to a firestop system’s ability to resist water passage through a floor assembly. In August of 2004, UL established a procedure to quantifiably measure a firestop product’s water resistance in buildings. To qualify as a Class 1 W-rated system, the firestop assembly must withstand a 3-ft head of water for 72 hours with no leakage. This new optional W-rating for water resistance joins UL’s other optional measure, the L-rating for air leakage, and the two required measures, F and T-ratings.

The F-rating establishes the minimum amount of time, under specified conditions, that a fire-rated assembly must withstand fire penetration and the T-rating expresses the amount of time that the firestop system will prevent the temperature of the non-flame side of the assembly from rising 325° above the ambient temperature.

While firestop systems are installed as a passive fire containment mechanism, sprinkler systems serve as active fire containment. Once triggered, sprinkler systems reduce the heat source by directly cooling the fire’s flames as well as dampening the fuel source by moistening the flammable materials feeding the fire. However, in the process of containing the fire the water source often does a great deal of damage to the remaining building structure by subsequently flowing through penetrations to the floors below. Hilti has approached this problem by developing the following line of products and systems that have successfully been tested to the Class 1 W-rating requirements: 

• CFS-DID Drop-In Device
• CFS-S SIL GG Firestop Silicone Sealant
• CFS-S SIL SL Firestop Silicone Sealant
• CP 606 Flexible Firestop Sealant
• CP 618 Firestop Putty Stick
• CP 620 Fire Foam
• CP 643N/644 Firestop Collar
• CP 648-E/S Firestop Wrap Strip
• CP 680-M/P/PX Cast-In Firestop Device
• CP 681 Tub Box Kit
• FS-ONE MAX High Performance Intumescent Firestop Sealant

These products were subjected to the standard 3-ft water column pressure test for 72 hours* followed by a fire and hose stream test in accordance with UL 1479. The Class 1 W-rating is listed on a variety of Hilti firestop systems covering the following penetrating material types:

• Bare metallic pipes, conduits or tubing
• Cable bundles 
• Insulated metallic pipes / tubing
• Multiple or mixed penetrants
• Non-metallic pipes, conduits or tubing
• Sheet metal ducts

While the W-rating is not mandated by code requirements, they are often noted by architects and engineers in specifications and requested by building owners who understand the importance of protecting their properties from water damage. Protect your multi-story project by adding W-rated products and firestop systems to your designs today!

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