The requirement for M4(3)2a is for a bathroom that is capable of simple adaptation at a future date to become wheelchair accessible in compliance with M4(3)2b. It need not be completed and delivered as a wheelchair accessible bathroom, but does need to be equiped with suitable services and adequate overall dimensions. The simplest way to demonstrate compliance is to design an accessible bathroom, and then modify the layout to meet the more relaxed requirements for an adaptable bathroom.