Some basic ADA guidelines are mandatory for single-user bathrooms. There should be 30 x 48 inch access to the sink. Keep in mind that the door can turn in this rectangle. The measurement should begin when the disabled person has a vertical space of 9 inches for the feet and approximately 27 inches for the knees.
When it was approved in 1990, the ADA did not require that all existing buildings be immediately modernized to ensure their accessibility. Instead, it is based on planned modifications (discussed here) and on the elimination of barriers (discussed in the lesson) to improve accessibility in older buildings over time. He says that when a company modifies an existing facility in a way that affects usability, the areas or elements that are modified must comply with ADA regulations. The rules for modifications are not always as strict as the rules for new buildings.
The section of the ADA Rules that analyzes alterations describes many situations in which less stringent provisions are allowed. In addition, the ADA recognizes that, sometimes, existing structural conditions cannot be modified without removing or altering a load element that is an essential part of the structure, or sometimes an existing physical or site restriction prohibits the modification or addition of accessible elements that fully comply with ADA regulations. In these cases, a company must comply with the provisions of the ADA Rules “to the greatest extent possible.” As for existing bathrooms that don't meet ADA standards, there must be a sign indicating the nearest ADA-compliant bathroom.