2010 ADA Standards for Accessible Design Pocket Guide
305.7 Maneuvering Clearance.
Where a clear floor or ground space is located in an alcove or otherwise confined on all or part of three sides, additional maneuvering clearance shall be provided in accordance with 305.7.1 and 305.7.2.
Alcoves shall be 36 inches (915 mm) wide minimum where the depth exceeds 24 inches (610 mm).
Alcoves shall be 60 inches (1525 mm) wide minimum where the depth exceeds 15 inches (380 mm).