A two-hour fire-resistance rating for a non-load-bearing partition is commonly achieved using a specific assembly of materials tested according to standards like ASTM E119. The assembly described in option D—metal studs with two layers of 1/2" Type X gypsum board applied to each side—is a standard, certified two-hour rated wall. The "Type X" gypsum board is critical; it has a specially formulated core with glass fibers that resist heat and prevent disintegration for a longer period than regular gypsum board. The two layers on each side provide the necessary mass and insulation to meet the two-hour requirement. The glass fiber insulation primarily improves acoustic performance but is also part of the tested assembly.

A: This assembly uses "regular" gypsum board, which lacks the fire-resistive additives of Type X and is insufficient for a two-hour rating.

B: A single layer of "regular" gypsum board on each side typically provides only a 30-minute fire-resistance rating.

C: This non-standard combination of one layer of Type X and one layer of regular board does not meet the requirements for a two-hour rated assembly.

1. Gypsum Association. (2021). Fire Resistance Design Manual (GA-600-2021). Hyattsville

MD. Design No. WP 1071 specifies a 2-hour fire-rated

non-load-bearing wall assembly consisting of 1-5/8" steel studs with two layers of 1/2" Type X gypsum wallboard on each side.

2. Ching

F. D. K. (2020). Building Construction Illustrated (6th ed.). John Wiley & Sons. In Chapter 7

"Wall Systems

" the section on Gypsum Board Partitions illustrates that a 2-hour fire rating is achieved with steel or wood studs faced on each side with two layers of 5/8" Type X gypsum board (p. 261). Two layers of 1/2" Type X is also a common tested assembly for this rating.

3. Mehta

M.

Scarborough

W.

& Armpriest

D. (2018). Building Construction: Principles

Materials

and Systems (3rd ed.). Pearson. Chapter 15

"Interior Walls and Partitions

" details fire-rated gypsum board partitions

indicating that a 2-hour rating requires two layers of Type X gypsum board on each side of the framing (Section 15.3.2).