2010 ADA Standards for Accessible Design Pocket Guide
505.10.2 Top Extension at Stairs.
At the top of a stair flight, handrails shall extend horizontally above the landing for 12 inches (305 mm) minimum beginning directly above the first riser nosing. Extensions shall return to a wall, guard, or the landing surface, or shall be continuous to the handrail of an adjacent stair flight. [S.H. 4.9.4(6)], [S.H. Fig. 19(d)]