is this a designated historic building? Sounds like a change of occupancy.
This is from the 2015 IEBC just for accessiblity:
1205.15 Accessibility requirements. The provisions of Section
1012.8 shall apply to facilities designated as historic
structures that undergo a change of occupancy, unless technically
infeasible. Where compliance with the requirements for
accessible routes, ramps, entrances, or toilet rooms would
threaten or destroy the historic significance of the building or
facility, as determined by the authority having jurisdiction,
the alternative requirements of Sections 1204.1.1 through
1204.1.4 for those elements shall be permitted
Exception: Type B dwelling or sleeping units required by
Section 1107 of the International Building Code are not
required to be provided in historical buildings.
also:
[BS] 1201.2 Report. A historic building undergoing repair,
alteration, or change of occupancy shall be investigated and
evaluated. If it is intended that the building meet the requirements
of this chapter, a written report shall be prepared and
filed with the code official by a registered design professional
when such a report is necessary in the opinion of the code
official. Such report shall be in accordance with Chapter 1
and shall identify each required safety feature that is in compliance
with this chapter and where compliance with other
chapters of these provisions would be damaging to the contributing
historic features. For buildings assigned to Seismic
Design Category D, E or F, a structural evaluation describing,
at a minimum, the vertical and horizontal elements of the lateral
force-resisting system and any strengths or weaknesses
therein shall be prepared. Additionally, the report shall
describe each feature that is not in compliance with these provisions
and shall demonstrate how the intent of these provisions
is complied with in providing an equivalent level of
safety.
There's more sections under change of occupancy.
If there are any repairs or alterations there are more sections.