Drywall (C-9) · Lesson 3 of 5

Fire-Rated Partitions: Layers, Offset Joints, and Board Takeoff

"Fire-Rated Partitions: Layers, Offset Joints, and Board Takeoff" is lesson 3 of 5 in the Drywall (C-9) Learning Hub. It opens with "A Rating Belongs to a Tested or Prescribed Assembly" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. A Rating Belongs to a Tested or Prescribed Assembly
  2. Two Steel-Stud Walls Printed in Table 721.1(2)
  3. Offset the Joints as Printed
  4. Fasteners and Joint Treatment in Rated Assemblies
  5. Count Board by Layers and Screws by the Printed Schedule

The worked example in the course applies this lesson to a realistic job in 7 steps, from "Wall area on one side" through "Plan the joints".

What you'll be able to do

  • Explain the main idea of "Fire-Rated Partitions: Layers, Offset Joints, and Board Takeoff" in plain language you can use on the exam.
  • Apply this step with confidence: "Offset the Joints as Printed".
  • Apply this step with confidence: "Fasteners and Joint Treatment in Rated Assemblies".
  • Apply this step with confidence: "Count Board by Layers and Screws by the Printed Schedule".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Fire-Rated Walls: Layers, Offset Joints, Board CountWALL THICKNESS, PLAN VIEW (to scale)1 HOUR (Item 13-1.1): 1 layer 5/8 in. each side5/8steel stud 1-5/85/82-7/8 in. face to face2 HOUR (Item 13-1.2): 2 layers 1/2 in. each side1/21/2steel stud 1-5/81/21/23-5/8 in. face to faceSCREWS PRINTED IN TABLE 721.1(2)Item 13-1.1: 1 in. No. 6 screws,8 in. o.c. perimeter, 12 in. middle studItem 13-1.2, layer 2: 1-5/8 in. screws,9 in. at vertical joints, 12 in. middle stud,24 in. along top and bottom runnersBOARD COUNT: 60 ft x 12 ft wallOne side: 60 x 12 = 720 sq ft2-hour: 2 sides x 2 layers = 4 layers4 x 720 = 2,880 sq ft of board4 x 12 ft sheet = 48 sq ft2,880 / 48 = 60 sheets+ 10% waste = 66 sheets1-hour: 2 layers x 720 = 1,440 sq ft1,440 / 48 = 30 sheets+ 10% waste = 33 sheetsLayer 1, one 4 x 12 sheet:Perimeter 2 x (144 + 48) = 384 in.384 / 8 = 48; middle stud 144/12 - 1 = 1148 + 11 = 59 screws per sheet2-hour = 66 sheets vs 33 for 1-hour; layer 1 takes 59 screws per sheetSources: 2025 CBC Table 721.1(2) Items 13-1.1, 13-1.2 and note d; CBC 703.2; CBC 2508.5.10% waste is an estimating assumption, not a code value. The listed assembly governs.CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: A Rating Belongs to a Tested or Prescribed Assembly

2025 CBC Section 703.2.1 says fire-resistance ratings are determined by the tests in ASTM E119 or UL 263. Section 703.2.2 also accepts analytical methods, including the prescriptive designs printed in Section 721. Table 721.1(2) lists complete wall assemblies (studs, board, layers, fasteners) with the rating each earns. If you add something that was not part of the tested or listed assembly, Section 703.2.1.4 requires data showing the rating is not reduced. Type X board is one part of the wall, not the rating by itself.

Step 2: Two Steel-Stud Walls Printed in Table 721.1(2)

Item 13-1.1 (1 hour): 0.018 in. (No. 25 gage) channel studs 24 in. o.c., one full-length layer of 5/8 in. Type X applied vertically, 1-in. No. 6 screws at 8 in. around the perimeter and 12 in. on the intermediate stud; 2-7/8 in. thick. Item 13-1.2 (2 hours): the same studs, two layers of 1/2 in. Type X each side, first layer screwed the same way, second layer with 1-5/8 in. No. 6 screws at 9 in. along vertical joints, 12 in. intermediate and 24 in. along the top and bottom runners; 3-5/8 in. thick. Both carry note d: nonbearing use only. The 2-hour wood-stud wall (Item 14-1.5) uses two layers of 5/8 in. Type X instead, so layer thickness depends on the framing.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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