Back-to-Back Certification Changes the Game
Key Highlights
-Allied Moulded’s new UL certification allows approved fiberglassBOX™ outlet boxes to be installed back-to-back in qualifying 2-hour fire-rated wall assemblies without requiring putty pads.
-By eliminating putty pads and reducing spacing restrictions, contractors can lower material and labor costs while simplifying installation on multi-family and commercial projects.
-The certification applies to a wide range of existing Allied Moulded fiberglassBOX™ products, giving engineers, distributors, and electricians greater flexibility without changing their current specifications or inventory.
For decades, electrical contractors have worked around the limitations of outlet box placement in fire-rated walls. Traditional requirements often meant maintaining separation distances between boxes installed on opposite sides of a wall or adding fire-resistant materials such as putty pads to maintain the wall's integrity. Now, Allied Moulded Products has simplified that process with an industry-first advancement: UL certification for back-to-back installation of fiberglassBOX™ outlet boxes in 2-hour fire-rated wall assemblies without the need for putty pads.
This new certification represents another milestone in Allied Moulded's long history of American innovation. For more than 65 years, the company has developed solutions designed to help electricians, contractors, engineers, and builders reduce installation challenges while maintaining code compliance and safety standards. The new back-to-back certification continues that tradition by delivering a practical solution that saves time, reduces costs, and streamlines construction projects.
What Back-to-Back Certification Means
The certification allows approved Allied Moulded fiberglassBOX™ nail-on outlet boxes to be installed directly opposite one another within the same wall cavity in qualifying 2-hour fire-rated wall assemblies. Unlike traditional installation requirements that typically require at least three inches of horizontal separation between boxes located in the same cavity, approved Allied Moulded boxes can now be mounted with less than three inches of separation or even directly on the same stud facing opposite wall surfaces.
This certification applies to walls constructed with a minimum 5½-inch-deep cavity using wood or non-load-bearing steel studs and gypsum wallboard assemblies with fire-resistance ratings of up to two hours. The UL certification specifically permits outlet boxes on opposite sides of the wall to be installed back-to-back while maintaining the wall's fire-resistance classification when installed according to UL CEYY.9379 requirements.
Perhaps most importantly, this certification applies not only to future purchases but also to current inventory of qualified products. Contractors and distributors can immediately benefit from the new certification without waiting for redesigned products or inventory transitions.
Eliminating the Need for Putty Pads
One of the most significant advantages of the certification is the elimination of putty pads in qualifying applications. Fire-rated installations frequently require putty pads to maintain compliance when outlet boxes are installed in close proximity to one another. While effective, putty pads add material costs and installation time.
By removing this requirement for approved back-to-back installations, Allied Moulded helps contractors reduce labor and material expenses while simplifying the installation process. Contractors no longer need to spend additional time applying fire-resistant materials around approved fiberglassBOX™ products in qualifying wall assemblies.
The cost savings can become substantial on larger projects. According to Allied Moulded's example, a 50-unit apartment complex with shared kitchen demising walls could require multiple putty pads per wall. Eliminating those materials can result in significant savings, while also removing the labor needed to install them.
Designed for Modern Construction
The new certification is particularly valuable for multi-family housing projects such as apartments, condominiums, duplexes, and similar developments. Architects frequently design mirrored floorplans where electrical devices need to be installed directly opposite each other on shared walls.
Under traditional approaches, meeting fire-rating requirements often added complexity to these installations. With Allied Moulded's back-to-back certification, electricians can more easily mirror layouts and streamline wiring plans while maintaining compliance with fire-rated wall requirements.
The certification is also beneficial for projects utilizing staggered stud construction. Since staggered 2x4 stud walls typically provide more than seven inches of cavity depth, approved fiberglassBOX™ products may be installed back-to-back in those assemblies as well, provided all applicable fire-rating requirements are met.
A Wide Range of Approved Products
The certification extends across a broad selection of Allied Moulded fiberglassBOX™ outlet boxes, covering single-gang through five-gang configurations, as well as round boxes. Approved series include models such as 1096, 1098, 1099, 2300, 2302, RD-42, 3300, 3303, 4300, 4304, 5305, 9327, 9335, 9336, 9343, 9350, 9351, 9352, 9365, and 9372, among others. Certain Vapor Seal® models carrying the V2 suffix are also approved for back-to-back installation in qualifying two-hour double-layer wall assemblies.
The extensive list of approved models gives engineers, specifiers, contractors, and distributors flexibility when designing projects and selecting products. Rather than limiting users to a small set of specialty products, Allied Moulded has made the certification available across a wide portion of its fiberglassBOX™ product family.
Built on Testing and Innovation
The certification is the result of rigorous testing conducted in partnership with UL. Allied Moulded notes that testing included configurations involving two five-gang outlet boxes installed directly opposite one another in the same stud cavity. These assemblies successfully met UL testing requirements for a 2-hour fire-rated wall when installed within qualifying wall construction featuring a minimum 5½-inch cavity depth.
This achievement reflects the company's ongoing commitment to innovation. According to Allied Moulded, its patented fiberglass formulation has evolved through years of product development and customer feedback focused on solving real-world installation challenges. The result is a practical certification that delivers measurable benefits without changing the products contractors already know and trust.
Installation Made Simple
At its core, Allied Moulded's back-to-back certification is about making electrical box installation simpler. By eliminating the need for putty pads, reducing spacing concerns, and allowing greater design flexibility within 2-hour fire-rated wall assemblies, contractors can complete installations more efficiently while maintaining confidence in compliance and safety requirements.
For electricians, builders, and designers looking to reduce complexity on multi-family and commercial projects, Allied Moulded's UL-certified back-to-back fiberglassBOX™ solution delivers a straightforward advantage: fewer materials, less labor, simplified layouts, and the trusted performance of a Made in the USA fiberglass electrical box.
For more information please visit: https://info.alliedmoulded.com/back-to-back-electrical-boxes
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