All alterations that could affect the usability of a facility must be made in an accessible manner to the maximum extent feasible. For example, if during renovations a doorway is being relocated, the new doorway must be wide enough to meet the new construction standard for accessibility.
When alterations are made to a primary function area, such as the lobby of a bank or the dining area of a cafeteria, an accessible path of travel to the altered area must also be provided.
The bathrooms, telephones, and drinking fountains serving that area must also be made accessible. These additional accessibility alterations are only required to the extent that the added accessibility costs do not exceed 20% of the cost of the original alteration. Elevators are generally not required in facilities under three stories or with fewer than 3,000 square feet per floor, unless the building is a shopping center or mall; the professional office of a health care provider; a terminal, depot, or other public transit station; or an airport passenger terminal.
See the 2010 ADA Standards for Accessible Design for more information regarding alterations: https://www.ada.gov/regs2010/2010ADAStandards/2010ADAstandards.htm
For additional information, take a look at the following resources:
FAQ: Is my building "grandfathered in" under the older 1991 ADA Standards for Accessible Design or do I need to comply with the 2010 ADA Standards?
FAQ: If I am doing a renovation on a hotel, how many guest rooms need to be accessible?
Fact Sheet: Overview of the 2010 Standards for Accessible Design