How is the thickness of gypsum board determined for drywall applications?

The correct answer is grounded in standard practices outlined in the International Residential Code (IRC) for drywall applications. Gypsum board thickness is typically specified based on the intended use and performance requirements.

For most standard interior walls, a thickness of 1/2 inch is common, providing adequate strength and durability. However, in circumstances where enhanced fire resistance is needed, such as in fire-rated assemblies, a thicker board, commonly 5/8 inch, is required. This thicker board provides additional protection against the spread of fire and increases the overall structural integrity of the wall system.

In this context, option A accurately reflects the guidelines and common practices for drywall thickness in both general and fire-rated applications. The other choices do not align with these established standards; for instance, 3/8 inch is generally not sufficient for most structural needs, while 5/8 inch for all applications lacks consideration for standard partitions, and 1 inch is excessive and impractical for most drywall uses.