Excerpted from " ADA Guide for Small Businesss" http://www.ada.gov/smbustxt.htm
Fixed Seating and Tables
If tables are provided, such as in restaurants and snack bars, and the tables are attached to the wall or floor (fixed), then 5% of the tables or at least one (if less than 20 are provided) must be accessible, if doing so is readily achievable. Accessible seating must be provided, if doing so is readily achievable, at each accessible table to accommodate people using wheelchairs. Movable chairs can be used for these tables and the movable chairs can be removed when customers using wheelchairs use the table(s).
The same requirements apply to fixed tables in outdoor areas such as picnic areas, playgrounds or patios.
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When fixed seating or fixed tables are provided, accessible seating must be provided, if readily achievable.
An accessible table has a surface height of no more than 34 inches and no less than 28 inches above the floor. At least 27 inches of knee clearance must be provided between the floor and the underside of the table. An accessible route provides access to each accessible table and a clear floor area 30 inches by 48 inches is provided at each accessible seating location. This clear floor area extends 19 inches under the table to provide leg and knee clearance.
If it is not readily achievable to provide the minimal number of accessible tables in all areas where fixed tables are provided, then the services must be provided in another accessible location, if doing so is readily achievable. However, these alternate location(s) must be available for all customers and not just people with disabilities. It is illegal to segregate people with disabilities in one area by designating it as an accessible area to be used only by people with disabilities.
notes:
Table height 34" maximum, 28" minimum
Knee clearance 27" minimum (from floor to bottom of table surface)
Clear floor area of 30" by 48" needed at each seating area
Knee clearance extends at least 19" under the table