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National Gypsum Compan

Analyzing the Assembly

What follows is an analysis and discussion of the details of one of UL’s fire-resistant assemblies. Additional exercises, intended to familiarize the readers with the process, will be part of the additional reading material at the end of this section.

How do you find an assembly when you do not already know the design number? Start by using the chart on page 1 of the UL Fire Resistance Directory Vol. 1 (Figure3).

Your first step will always be to determine your Group of Construction in the far left-hand column. Does your project’s floors-ceilings call for concrete and cellular steel floor? If so, your design will start with A, B or C. Are you looking for a fire rated wall or Partition assembly? Your desired design will start with a U, V or W.

Next decide what type of protection your project will utilize (moving right across the chart). Your first choice is “Membrane Protection.” Membrane Protection refers to the mechanical fastening of protection to the structure, as gypsum wallboard is fastened to studs. Some other building materials that are within the Membrane Protection category are concealed grid and metal lath. Our next option is “Direct Applied Protection,” protective materials like mastics or spray-applied fire-resistive materials. The last column is “Unprotected.” Unprotected refers, generally, to brick or block masonry.

To review, look for your Group of Construction first and then scan over to your desired type of protection. The intersection of these two items will determine the design numbers that are suitable for your project.

The chart on page 1 of the UL Directory Vol. 1 is the same as the chart online at the UL website. So if you follow the same instructions online you will find a design suitable for your project (Figure 3).

As promised, this is an exercise to assist you in getting comfortable in using the table on page one of Vol. 1. Starting with your Group of Construction…

Question: What is an assembly number for a wall & partition system with Metal Stud, Gypsum Board, Lath and/or Plaster ?

Refer to the Numbering System for Fire Rated Assemblies chart. In the first column, you select the type of construction and then look across for the series with gypsum board.

You should come up with the letter designation U, V or W, and 400-499 series. An assembly that would fall under this designation is v438 (Figure 3).

UL Design No. V438 is a non-load bearing steel stud wall design with hourly ratings for 1,2,3 and 4 hours. You can see from the drawing that both a one- hour (left) and four-hour (right) wall is detailed. The call-out numbers on the drawing correspond with the numbers in the text.

Item 1 tells us that floor and ceiling runners are not shown but must be channel-shaped from a minimum 25 MSG corrosion-protected steel. Minimum sizes and screw patterns are also addressed.

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