In walls constructed of what material may the front edge of an outlet box be set back up to 1/4 inch?

When installing outlet boxes, the materials used for wall construction influence the positioning of the front edge of the box. For walls made of Sheetrock, it is permissible to set back the front edge of an outlet box up to 1/4 inch. This allowance accommodates the thickness of the faceplate that will be covering the box, ensuring a flush finish without protruding parts.

In contrast, materials such as concrete, wood, and brick do not have this same allowance because they have different installation standards and requirements. For example, a concrete wall requires the outlet box to be flush with the surface to maintain structural integrity and ensure safe electrical installation. Similarly, wooden and brick walls have specific installation practices that necessitate different positioning for outlet boxes to ensure secure mounting and safety compliance. Thus, the correct answer reaffirms the unique requirements associated with Sheetrock in outlet box installation.