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Putty Pads: Why, where, and when are they required?

Putty PadsWhy?

Code requires fire barriers to hold back the products of combustion (flames, heat, smoke and gasses). Where electrical boxes penetrate one or both membranes of a fire rated wall they provide a direct path for heat to be transferred more readily through the assembly, and puttyFirestopping, non-hardening, compound designed to seal through-penetrations as well as certain membrane penetrations against the spread of fire, smoke and toxic gasses. pads act as a barrier to minimize temperature rise on the non-fireside of the wall.


Putty Pads are designed to be installed over the back of electrical boxes, and should be molded to cover fittings and "pie crusted" to form a seal against the drywall and stud. It is not necessary to fit the putty pad between the stud and the box.


According to code, putty pads are required where any one of the following conditions exists:

  1. When greater than 100 square inches per 100 square feet of wall space is compromised by electrical boxes. This includes both sides of the wall, and if the "100" per 100' " is exceeded, all boxes must be covered to comply with code.
  2. When boxes are installed on opposing sides of the wall within 24" horizontally, regardless of the vertical position of the boxes. Boxes in violation of the 24" rule should be protected with putty pads so that no two boxes on opposing sides of the wall within 24" horizontally exist. Both boxes within the area must be protected. Protecting a single box is not adequate to maintain the hourly rating of the wall.
  3. If the size of the electrical box exceeds 16 square inches, it must be protected. Putty pads have been tested on boxes as large as 4-11/16 by 4-11/16. Boxes larger than 22 square inches commonly are "five-sided" with drywall, a practice which UL supports.

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This expert advice section has been developed with the help of designers, installers, inspectors and firestop manufacturers. It is a compilation of frequently asked questions on firestop technology, code compliance, UL system information and installation recommendations. We welcome your questions and/or suggestions for additional content.