Answers to questions frequently asked by architects. Click on the question to view the answer.


1. What modifications can be made to a UL certified assembly?

2. What is an engineering judgment?

3. Does UL perform engineering judgments?

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

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


1. Where is the sound transmission class (STC) rating listed for a design?

2. Can the ceiling suspension system be lowered?

3. How do I determine the hourly rating of an existing “UL Labeled” door?

4. Where do I find information regarding the fire resistance for common materials like wood, concrete, etc.?

5. Where do I find information regarding the fire resistance of archaic materials?

6. Are there fire-resistant wall designs that include gypsum board on one side of a metal stud?

7. Can a wall design be used in a horizontal application, for example, as a soffit? If not, is there a tested design for this application?

8. Why can't I find a design? What happened to the design I used to specify?

9. I need designs that include wood joist 2 x 8’s and 2 x 10’s. Can you help?

10. Why are dampers and exhaust fans specified in some designs and not others?

11. Understanding the Contents of a Tested Design

12. Are there any tested floor-ceiling or roof-ceiling designs that specify a wood joist (2x10, “I”-shaped or parallel chord) that incorporate a wood beam (like an LVL) or steel beam?

13. What is the difference between a “Restrained” and “Unrestrained” rating?


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

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

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

4. How do I find an assembly for exterior use?


1. How do I get a copy of an architect chat transcript?

2. How do I get an assembly tested that I have designed?

3. Does UL permit its certification information to be copied and placed on the project plans?

4. Does UL offer any training courses for architects?

5. Does UL certify products relating to sustainability and green building design?

6. How can I communicate with UL technical staff if questions arise?

7. Are CAD drawings of the tested assemblies available?


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

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