RECOMMENDED MAXIMUM STAIR TREAD LENGTHS*
* For treads up to 5'-6", maximum tread lengths are based on 300
lb. concentrated load on the front 5 inches of tread, at center of
tread length, and deflection limited to 1/240 of tread length. When
treads exceed 5'-6" in length, design allows for 300 lb.
loads at 1/3 points of tread length.