28 CFR Part 35 Title II Notice of Proposed Rulemaking (NPRM) (published 2008)

(i) Primary function.  A primary function is a major activity for which the facility is intended.  Areas that contain a primary function include, but are not limited to, the meeting rooms in a conference center, as well as offices and other work areas in which the activities of the public entity using the facility are carried out.

(A) Mechanical rooms, boiler rooms, supply storage rooms, employee lounges or locker rooms, janitorial closets, entrances, and corridors are not areas containing a primary function.  Restrooms are not areas containing a primary function unless the provision of restrooms is the principal purpose of the area, e.g., in highway rest stops.

(B) For the purposes of this section, alterations to windows, hardware, controls, electrical outlets, and signage shall not be deemed to be alterations that affect the usability of or access to an area containing a primary function.