Question

what condition may permit a toilet and bath to be windowless?
floor area below 2.00 sqm automatically waives ventilation rules.
shared air shafts remove the need for mechanical systems.
doors may be left open during use to allow air exchange.
provision of a mechanical exhaust system per nbcp ventilation requirements.

Explanation:

In building regulations for bathrooms and toilets, a mechanical exhaust system can meet ventilation needs allowing for window - less designs as per standards like NBCP.

Answer:

Provision of a mechanical exhaust system per NBCP ventilation requirements.