I know of all things why an article about toilet seats. There is really only one ADA requirement…the seat height. While that is true you should also consider the requirements in the International Plumbing Code.
ADA Requirements
604.4 Seats. The seat height of a water closet above the finish floor shall be 17 inches (430 mm) minimum and 19 inches (485 mm) maximum measured to the top of the seat. Seats shall not be sprung to return to a lifted position.
Water Closet Seat Height
When you specify a water closet make sure you select the ADA Compliant or Barrier Free types. The accessible water closets will have the bowl a little higher so that when the seat is installed it will be at the correct height. For example, the ADA Compliant image below states Barrier Free on the cut sheet while the Non-ADA Compliant image does not.
ADA Compliant Water Closet
Non-ADA Compliant Water Closet
International Plumbing Code Requirements
The International Plumbing Code (IPC) is a standard code that sets minimum requirements for plumbing systems in commercial projects. Municipalities will require adherence to this standard when submitting drawings for permit. Just like the ADA they have standards for water closet seats.
When selecting the water closet in commercial construction the IPC requires the water closet bowls be of the elongated type, rather than the round type you usually see in residential homes. Also, they require that the elongated bowl have a seat that is of the hinged open-front type. They do make closed-front type seats but these are typically used for residential homes.
The International Plumbing Code (IPC) requires the following:
425.2 Water Closets for Public or Employee Toilet Facilities:
Water closet bowls for public or employee toilet facilities shall be of the elongated type
425.3 Water Closet Seats
Water closets shall be equipped with seats of smooth, nonabsorbent material. Seats of water closets provided for public or employee toilet facilities shall be of the hinged open-front type. Integral water closet seats shall of the same material as the fixture. Water closet seats shall be sized for the water closet bowl type.
Elongated Open Front Toilet Seat