Hello. We have an existing WP 1052 1 HR rated wall (3 5/8" metal stud w/ 1 layer of gyp on one side and 2 layers of gyp on the other side) between classroom spaces. New audio visual electrical devices will be installed on both sides. The contractor is asking whether it is acceptable to install back to back electrical boxes within the same 16 inch stud cavity, without compromising the fire and acoustical rating of the wall? The contractor will be using Hilti Firestop CP 617 putty pads on the electrical boxes. Thank you.
Hello,
Thank you for reaching out to the Hilti Fire Protection Design Team to assist you with your firestop engineering needs. We have the CLIV (attached) that addresses back-to-back box applications. However, if you fall outside the parameters of the CLIV, then we can address your application through an Engineering Judgment which will be a custom detail showing your exact application with the firestop components required to maintain the stated ratings.
Hilti is proud to announce the launch of our engineering website, the HILTI CONSTRUCTION PLATFORM (HCP). This platform will be the home for all of your Fire Protection Engineering needs, including Engineering Judgment requests. You can find more information on how to access this new platform here: https://www.hilti.com/ej (US) or https://www.hilti.ca/ej (Canada.)
Along with HCP, Hilti is excited to announce our new mobile app for all your firestop needs: Hilti Firestop Selector. Using the Firestop Selector app gives you easy access to the Hilti Fire Protection Design Team from the jobsite, on the road, or in the office to request a new EJ, an EJ Revision, or ask a Question anytime, anywhere. You can download the app using the Google Play Store or Apple App Store.
If you have any questions, please reach out to our customer service team at 1-800-879-8000 (US) or 1-800-363-4458 (Canada) for assistance.
Thank you,
Jessica Starks
Senior Fire Protection Engineer
Hello Jessica, and thank you for your reply. The electrical boxes in this case would be placed in the same 16 inch stud cavity, one from Room A, and the other from the adjacent Room B. There would be a horizontal gap between the two electrical boxes, but it would be less than 24 inch. I understand this is not considered back to back, as the outlet boxes are horizontally separated by a small distance. Please confirm if this is correct.
If correct, would using the Hilti putty pad around one of the electrical boxes keep the fire and acoustic rating of the wall intact? Thank you.