Understanding Putty, Pads, And Box Inserts
A penetration that only affects one side of a rated wall is referred to as a membrane penetration. Such penetrations occur most frequently due to the installation of recessed electrical boxes. The International Building Code (IBC), which is adopted in most US jurisdictions, requires recessed fixtures be installed such that the fire resistance rating of the wall not be reduced. One way to prevent boxes from reducing the walls fire rating and thus meet the IBC performance requirement is by using putty pads or other listed materials. The Hilti CP 617 or CFS-P PA Firestop Putty Pad and Hilti Firestop Box Insert areproducts that are often chosen, but many times the application range and specific code requirements are misunderstood. The IBC lists the specific requirements for electrical outlet boxes (membrane penetrations), explaining what protection is needed to maintain the rating of the wall assembly. This document will focus on the requirements of Section 713.3.2 of the 2009 IBC (Section 714.3.2 of the 2012 IBC). Opinions of Hilti, Inc. are advisory only. The final interpretation of any code issue is the legal responsibility of the building official or AHJ.
All recessed electrical boxes (e.g. outlet, switch) and the rules that govern them can basically be broken down into three categories:
- Steel outlet boxes that do not exceed 16 sq. in.,
- Steel outlet boxes that do exceed 16 sq. in., and
- Non-metallic outlet boxes of any size
Metallic electrical boxes that do not exceed 16 square inches (e.g., 4” x 4”)
This size and type of electrical box is the most complex when it comes to code requirements. The 2009 IBC permits the installation of unprotected steel outlet boxes not exceeding 16 sq in within a rated wall assembly as long as the sum total area of openings does not exceed 100 square inches for any 100 sq. ft. of wall. In addition the code has specific requirements for the spacing of steel electrical boxes (max. 16 sq. in.) located on opposite sides of wall. Steel electrical boxes that do not exceed 16 square inches (4” x 4”) installed on opposite sides of wall should be separated by one of the following:
- A horizontal distance of not less than 24”
- A horizontal distance greater than the depth of the wall cavity when the wall cavity is filled with rockwool, slag mineral wool insulation or cellulose loose-fill
For example, if you have solid 2 x 4 studs, max. 16 sq. in. steel electrical boxes do not have to be protected if boxes on opposite sides of the wall are installed at least 3-1/2” apart if the wall cavity is insulated with one of the materials above.
- Solid fire blocking, including nomina 2” thick lumber (steel studs are not considered acceptable fire blocking materials)
- Other listed materials or methods (i.e., putty pads and other wall opening protective materials). UL lists these materials under code category CLIV. The individual Classifications within this category (CLIV) Wall Opening Protective Materials indicate the specific applications and the method of installation for which the materials have been evaluated.
In accordance with Hilti’s CLIV approval, when CP 617 or CFS-P PA Firestop Putty Pad or Firestop Box Insert are installed on boxes on both sides of a wall as directed, the horizontal separation between outlet boxes on opposite sides of the wall may be less than 24” provided that the boxes are not installed back to back (unless otherwise noted). While UL claims that wall opening protective materials could potentially be used to increase the allowable density of boxes installed within 100 sq. ft. wall, no manufacturer currently has this approval, including Hilti. Please reference the Table 1 on Page 4 for specific approvals for metallic electrical boxes that do not exceed 16 sq. in.
Metallic electrical boxes that do exceed 16 sq. in. (e.g., > 4” x 4”)
The 2009 IBC does permit other sizes of steel electrical boxes, but these boxes must be installed as they are tested and in accordance with the instructions included in the listing. In accordance with the 2009 IBC all steel electrical boxes larger than 16 sq. in. must be protected in some manner, regardless of the spacing to other boxes on the opposite sides of wall. Approved methods can once again be found in UL’s CLIV category.
In accordance with Hilti’s CLIV approval, CP 617 or CFS-P PA Firestop Putty Pads can be installed on metallic boxes up to 14” x 4” x 2-1/2” deep. Hilti Firestop Box Insert can be installed on steel boxes up to 4-11/16” x 4-11/16” and 4-1/2” x 8-1/2”. Again, all boxes larger than 16 sq. in. should be protected in some manner regardless of spacing on opposite sides of wall. Please reference the Table 3 on page 5 for specific approvals for metallic electrical boxes that exceed 16 sq. in.
Non-metallic electrical outlet boxes
The 2009 IBC does permit non-metallic electrical boxes, but these boxes must be installed as they are tested and in accordance with the instructions included in the listing. UL has a separate category for non-metallic outlet and switch boxes for use in wall or partition assemblies. Approved boxes can be found in Outlet Boxes and Fittings Classified for Fire Resistance (CEYY). The information provided for each classification includes the model numbers for the classified products, a description of the rated assemblies, the spacing limitations for the boxes and the installation details. This means that the spacing requirements on opposite sides of the wall are dependent upon the type of box being installed. Take for example this:
Approval from Allied Molded Products: Series 1082, 1084, 1085, 1086, 1088, 1096, 1098, 1099, 2300, 2301, 2302, 3300, 3303, 9301, 9302, 9304, 9305, 9307, 9312, 9313, 9318, 9323, 9324, 9327, 9328, 9331, 9332, 9333, 9334, 9335, 9336, 9337, 9338, 9339, 9340, 9342, 9343, 9344, 9350, 9351, 9355, 9356, 9358, 9361, 9363, 9364, 9365, 9366, 9368, 9369, 9370, 9372, 9390, 9395, RD-38 nonmetallic outlet and switch boxes with various suffixes for use in 1 and 2 hr fire rated gypsum board/wood stud wall assemblies framed with min 3-1/2 in. wide wood studs and constructed as specified in the individual U300 Series Wall and Partition Designs in the Fire Resistance Directory. Clearance between boxes and cut-outs in wall shall not exceed 1/8 in. The area of openings for boxes shall not aggregate more than 100 sq in. per 100 sq ft of wall or partition area with no opening exceeding 22.0 sq. in. Outlet and switch boxes on opposite sides of a wall or partition within the same stud cavity shall be separated by a horizontal distance of not less than 3 in. Boxes are suitable for installation in staggered stud wall configuration. Outlet and switch boxes on opposite sides of the wall and in separate stud cavities may be separated by a horizontal spacing of not less than 1-1/2 in. Any of the above listed boxes can be installed unprotected (w/o putty pads or inserts) within rated walls as long as the total area of opening for boxes does not exceed 100 sq. in. per 100 sq. ft. of wall. The listing also permits these specific boxes to be installed as close as 3” apart on opposite sides of wall with no additional protection needed.
In accordance with Hilti’s CLIV approval,
CP 617 or CFS-P PA Firestop Putty Pads can be installed on non-metallic boxes. Currently, Hilti has no approval for use of the Firestop Box Insert with non-metallic boxes. When CP 617 or CFS-P PA Firestop Putty Pads are installed on boxes on both sides of a wall as directed, the horizontal separation between outlet boxes on opposite sides of the wall are permitted to be less than what is currently allowed per the listing for the specific nonmetallic box, provided that the boxes are not installed back to back. Most non-metallic electrical boxes require 24” horizontal separation between boxes on opposite sides of a wall if they are not protected with putty pads. Please reference Table 2 on Page 4 for specific approvals for non-metallic electrical boxes.
The 2009 IBC is specific on the requirements for membrane penetrations by metallic and non-metallic recessed electrical boxes in rated gypsum walls. However it may be possible to install the boxes under less stringent conditions when such boxes are used in conjunction with wall opening protective materials such as Hilti CP 617 or CFS-P PA Firestop Putty Pads and Firestop Box Inserts. Currently use of wall opening protective materials may allow for (1) reducing the spacing between boxes contained on opposite sides of the wall and/or (2) increasing the size of the boxes. There are currently no UL listings for Wall Opening Protective Materials that would allow box density to be increased beyond the code-allowed 100 square inches per 100 square feet of wall area. The individual
Classifications within this category (CLIV) indicate the specific applications and the method of installation for which each specific product has been evaluated, which should be reviewed prior to installation.