Membrane Penetrations in Fire Resistance Rated Walls: Key Considerations and Standards

Membrane penetrations help protect electrical boxes in fire-resistance rated wall assemblies and are an essential part of fire safety to maintain model code required fire containment. To achieve the expected hourly fire-resistance rating, these assemblies must be constructed and maintained according to the criteria in the UL Solutions design and installation specifications. If the outer membrane of the wall assembly includes penetrations or recessed fixtures, these are required to be protected to maintain the hourly fire resistance-rating.

Membrane penetrations versus through penetrations

There are two types of penetrations to be considered. A through penetration has an opening that passes entirely through a fire-resistance rated assembly, whereas a membrane penetration has an opening that only passes through one side of the assembly. For example, a recessed electrical box mounted in a gypsum board wall surface of a fire-resistance rated wall, with conductors in the wall cavity is a membrane penetration. The focus of this article is UL Certified products for membrane penetration.

Code requirements for membrane penetrations

The International Building Code (IBC) requires membrane penetrations of fire-resistance rated assemblies by recessed fixtures to be protected so that the required fire resistance is maintained. It includes specific conditions by which electrical boxes may be installed in the wall. There are prescriptive Exceptions to the IBC requirements that recognize conditions under which recessed steel electrical boxes on opposite sides of a wall are protected with listed putty pads or are separated by other listed materials and methods.

UL Classifications for membrane penetration

UL Solutions classifies putty pads and other listed materials and methods under the UL Solutions product category Wall Opening Protective Materials (CLIV or QCSN). This category covers three types of technologies: putty pads, insert pads and gaskets. Putty pads are putty-like products installed on the outer surfaces of an electrical box prior to installation in the gypsum board membrane on the wall. Insert pads are for installation on the inside back surface of the box. Finally, gaskets are for installation under the cover plate of the box. The latter two products may be installed after the gypsum membrane is in place. Each of these products are Classified for use in specific types of fire-resistive designs when installed in accordance with the details provided in each Classification.

The information in each Classification includes:

• The model numbers covered.
• The type and size of electrical box covered.
• A description of the fire-resistance rated wall assembly.
• The specific method for the installation of the product.
• The type of cover plate covered.
• The required spacing between boxes on opposite sides of the wall.

Nonmetallic boxes in fire-rated assemblies

The Wall Opening Protective Materials section also permits the installation of nonmetallic electrical boxes in fire-resistance rated wall assemblies when the boxes are tested for use in fire-resistance rated walls and are installed in accordance with the instructions provided with the listing. Unlike metallic boxes, nonmetallic boxes intended for use in fire-resistance rated assemblies must be specifically listed for use in such assemblies.

UL Solutions classifies nonmetallic electrical boxes under the product category Outlet Boxes and Fittings Classified for Fire-Resistance (CEYY or QBWY). These nonmetallic boxes are Classified for use in specific types of fire-resistive designs when installed in accordance with the details provided in each Classification.

The information in each Classification includes:

• The model numbers covered.
• A description of the fire-resistance-rated wall assemblies covered.
• The annular space between the box and the wall membrane.
• The spacing limitations for the boxes.
• Other specific requirements or limitations of the Classification.

The electrical boxes covered in this category are required to be marked with the UL in a circle located in the base of the box, Class X hr, where X indicates the maximum hourly rating (i.e., 1 hr or 2 hr), and F, W, and/or C, where F = Floor, W = Wall, and C = Ceiling.

Classifications for putty pads, insert pads, gaskets and nonmetallic electrical boxes can be found online using Product iQ®.