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Answers to questions frequently asked by Architectural, Engineering, and Construction (AEC) professionals. Click on the question to view the answer.


How can I search for UL certified Wall-opening Protective Materials that can be used to protect electrical boxes that create a membrane penetration in fire resistance-rated wall Designs?

There is an exception for certain size and number of electrical boxes that can penetrate the membrane of a fire resistance-rated wall Design that can be found in the BXUV GuideInfo:

Metallic Electrical Outlet Boxes

Certified single- and double-gang metallic outlet and switch boxes with metallic or nonmetallic cover plates may be used in bearing and nonbearing wood stud and steel stud walls with ratings not exceeding 2 h. The metallic outlet or switch boxes should be securely fastened to the studs and the opening in the gypsum board facing should be cut so that the clearance between the box and the wallboard does not exceed 1/8 in. The surface area of individual metallic outlet or switch boxes should not exceed 16 sq in. The aggregate surface area of the boxes should not exceed 100 sq in. per 100 sq ft of wall surface. The aggregate surface area of the boxes may be exceeded when Wall-opening Protective Materials (CLIV) are installed according to the requirements of their certification.

Metallic boxes located on opposite sides of walls or partitions should be separated by a minimum horizontal distance of 24 in. This minimum separation distance between metallic boxes may be reduced when Wall-opening Protective Materials (CLIV) are installed according to the requirements of their certification.

Metallic boxes should not be installed on opposite side of walls or partitions of staggered stud construction unless wall-opening protective materials are installed with the metallic boxes in accordance with certification requirements for the protective materials.

Where the size, number or concentration of electrical boxes is outside the specifications described above, a certified Wall-opening Protective Material can be specified to meet applicable code requirements. These materials can be found by searching UL product categories CLIV and QCSN

Can the fastener size specified in a UL fire resistance-rated assembly be increase?

Yes. Unless a limitation of tolerance is noted in the individual design, the fasteners identified in UL designs are considered minimums.

If I add an additional layer of gypsum, or increase the thickness, can I achieve a higher fire resistance rating?

According to section II, Subsection 9 of the BXUV Guide Information, Gypsum board thicknesses specified in specific UL designs are the minimums. Additional layers of gypsum or greater thicknesses of gypsum board are permitted in any UL design, provided the fastener length is increased to provide penetration into framing that is equal to or greater than that achieved with the specified gypsum board thickness and fasteners.
There is no corresponding increase in the hourly fire resistance-rating for adding layer(s) or increasing thickness of gypsum. Fire resistance-ratings are determined by the specified construction in the design based on the UL 263 fire test.

Can I substitute Fire-retardant-Treated Wood for Gypsum in a UL Design?

No. Fire-retardant-Treated Wood cannot be substituted for gypsum in any UL Design. Fire-retardant-Treated Wood may be added to a UL Design following the requirements for adding wood structural panels found in the UL BXUV Guide Information for Wood Structural Panels (General) and Wood Structural Panels in Wall Assemblies.

Can I add structural wood panels like plywood to a wall assembly?

Yes. The addition of wood structural panels in fire rated gypsum board wall assemblies is permitted as follows:

  • Wood structural panels that are 4 ft. wide, minimum 7/16 in. thick oriented strand board (OSB) or 15/32 in. thick structural sheathing (plywood) complying with DOC PS1 or PS2, or APA Standard PRP-108, manufactured with exterior glue, may be applied horizontally or vertically to the framing members.
  • Vertical joints should be centered on studs, and staggered one stud space from the gypsum board joints.
  • The wood structural panels are permitted to be applied either as (1) a base layer (directly to the wall framing and under the gypsum board), (2) in between gypsum board layers, or (3) over the top of the completed gypsum board wall.
  • When wood structural panels are used on top of the gypsum board layers of exterior wall assemblies, the wood structural panel should be protected from the exterior environment either as specified in the design or as specified here.
  • When wood structural panels are added to wall assemblies that include furring channels, there should be no more than two layers (either gypsum board or wood structural panel or combination thereof) attached to the furring channel.
  • When wood structural panels are added to the wall assembly, the length of the fastener used for the outermost layer (either gypsum board or wood structural panel) should be sized appropriately to accommodate the additional thickness of the wall panel.

Can a larger wood or metal stud be used than what is specified for a specific UL wall assembly?

Wood and/or metal studs specified in UL Rated Designs are minimum sizes. Larger dimensional studs can be substituted.

What is an engineering judgment?

An engineering judgment is a method or process used to resolve field needs when a tested design, system or assembly is not available. The engineering judgment results in a letter or report being issued by some knowledgeable party, which evaluates the impact of modifications to published fire resistance designs, firestop systems, etc. To be effective the engineering judgment must be acceptable to the code authority and should be site specific.

What modifications can be made to a UL certified assembly?

UL certified assemblies are intended to be constructed as shown in individual designs. If a construction element is identified as ‘optional’ or ‘may be provided’ it is not mandatory and doesn’t need to be included in the construction. Also, if a design specification is indicated as a minimum or maximum, the construction can include greater or lesser thicknesses or dimensions respectfully. Additional variances for designs are included in the BXUV Guide Information for Fire-resistance Ratings. Modifications not covered above may be evaluated using an engineering judgment.

II. Technical Evaluation Developer Program

What is the Technical Evaluation Developer Program?

UL Solutions is offering current UL Solutions firestop customers a management system qualification program that includes requirements intended to increase the level of independent oversight for technical evaluations prepared by these customers.

This Technical Evaluation Developer Program is intended to improve the content and quality of engineering decisions related to fire containment products and systems, such as: perimeter fire barriers, firestopping of penetrations, linear joints and duct products.

Any established UL Solutions customer (applicant) with firestopping type products who utilize UL for certification, notified body or conformity assessment services in accordance with U.S., Canadian, UK or European standards can participate in the program.

For more information please visit the Technical Evaluation Developer Program page.

How are manufacturers who are enrolled in this program identified?

Manufacturers who are enrolled in this program will have their company name and scope of participation posted in the UL Solutions Product iQ® tool under authorized service providers.

What is the selection criteria used to select an evaluation report for laboratory testing?

UL Solutions will randomly select technical evaluations for laboratory testing across different product types and firestop solutions. Random selection reinforces the concept that the evaluation writer should always develop a solution based on test data.

What happens if a laboratory test of a selected evaluation determines that the system fails the certification test?

The test sponsor will be given the opportunity to review the results of the test, propose alternate solution and re-test the system. If continued non-compliances occur, the test sponsor would be subject to possible suspension or be dismissed from the program.

Does this UL Solutions program require the evaluation include specific information/detail? If so, what is specifically required?

The UL Solutions Program Requirements document does provide for specific information and details which are to be included in each technical evaluation. Examples of specific details include ratings (F,T, L, M, W), installation conditions, materials to be used and project location. The evaluations may also include pictures, drawings or schematics for product use and installation at the manufacturer’s discretion.

Does UL Solutions intend to publish results of non-conforming tests?

The results from non-conforming tests are proprietary and confidential to the test sponsor. Non-conforming results will not be disseminated, published or made available.

Can I review the Program Requirements for the Technical Evaluation Program?

Yes, the complete Program Requirements are available as a download from the Technical Evaluation Developer Program service page.


How do I find fire rated walls, floors beams and columns?

Most assemblies can be found by searching with specific parameters using the UL Product iQTM online tool. Guidelines for finding designs can be locatedHERE.

How do I reduce the number of assemblies found within a search?

  1. Leave the hourly rating blank. Sponsors of the tested designs typically want to achieve the highest rating possible: the materials you would like to specify might have a higher hourly rating than you require.
  2. You must be precise when entering the manufacturer’s name. If you are unsure, try using the keyword box.
  3. Keywords are only useful if the word or its derivative is contained within the design. Trade names or abbreviations like, “drywall”, “TJI”, “CMU”, “wide flange”, etc. will not work.
  4. Examples of useful keywords: “siding”, “stucco” “exterior” (walls with exterior finishes); “damper” (designs tested with dampers); U300, U400, etc (finding a fire rated joint based on a wall series type).

Are wall assemblies tested for exposure to fire on both sides?

Yes. The ratings for walls and partitions apply when either face of the assembly is exposed to the fire unless indicated otherwise in a specific design.

How do I find an assembly for exterior use?

Assemblies are investigated with the understanding that their use is limited to interior applications unless otherwise specified in the individual designs. Where an exterior application of a UL-certified design is desired, the code should be reviewed to ensure compliance with other code requirements applicable to exterior walls such as weather protection, water resistance, and vapor retarders.



How do I know if a tested design is tested for acceptance in the United States or Canada or both?

  • All designs found on the online search tool Product iQTM have been tested to US ANSI/UL 263 and CA ULC-S101. Therefore accepted in both countries. This is documented in the heading of every design.
  • Designs found on the ULC (UL Canada) Online Directories have been tested to CA ULC-S101, and therefore accepted only in Canada.

How do I know if a fire-resistance rated assembly is certified to Canadian standards?

cUL assemblies – Many US designs have also been certified for use in Canada. If the title of a design includes BXUV7 – Fire Resistance Ratings – CAN/ULC-S101 Certified for Canada, it has been investigated to Canadian standards and is intended for installation in accordance with Canadian building codes. Any loading or other restrictions noted on the design should be considered in the installation. For additional information see the General Information for Fire Resistance Ratings – CAN/ULC-S101 Certified for Canada link on the top of the design. To locate Canadian cUL designs in Product Spec, enter the desired design parameters, along with keyword “BXUV7”.

ULC assemblies – ULC fire-resistance rated assemblies can be found in the ULC Online Certifications Directory under Fire-Resistance Rated Assemblies. To find an assembly that meets your project specifications, scroll down to the NUMBERING SYSTEM FOR FIRE-RATED ASSEMBLIES table and use the hyperlinks in the table to locate the types of construction needed (e.g. floor-ceiling, beams, roof-ceilings, walls and partitions or columns) and the type of protection anticipated in the installation. Clicking on the corresponding hyperlinks in the table will result in a list of available ULC designs that can be opened and reviewed individually.