41 C.F.R. § 105-8.152
(b) Prior to the assignment or reassignment of space to an agency, GSA shall inform the agency of the accessibility, and/or the absence of accessibility features, of the space in which GSA intends to locate the agency. If the agency informs GSA that the use of the space will result in one or more of the agency's programs being inaccessible, GSA shall take one or more of the following actions to make the programs accessible:
(3) Take any other actions that result in making this agency's programs accessible.
The responsibility for payment to make the physical changes in the space shall be assigned on a case-by-case basis as agreed to by GSA and the user agency, dependent on individual circumstances.