Are statutory ventilation requirements based only on the whole home?

No. The regulations for a residential function set requirements for both occupied zones and individual occupied rooms. In new-build, the minimum capacity is linked, among other things, to floor area, with a minimum per room. For a central system, there is also a requirement for the total capacity of the connected occupied zones. The regulations thereby set a lower limit for capacity and availability; they do not require a system to continuously control based on measured IAQ per room.