David and Joe,
Lap for mesh is in ACI 318 12.18 and 12.19. It has nothing to do with an absolute distance, but depends on the crosswire spacing. If you read the weld shear requirement section of ASTM A 185, though you may want to increase the lap. It is easy to use WWR with a strength that is not completely developed by two wires.
Precast Concrete Engineer
Winchester, Virginia