A question about mechanical ventilation if I may. As I understood it any new kitchen, bathroom (bath/shower room) toilet (WC) or utility with no openable window should be provided with a mechanical extract fan to reduce condensation and remove smells. if you do have an openable window, don't need to worry about mechanical ventilation . The necessary performance of these extract fans is normally measured in litres per second (l/s) as follows: ·Kitchen - 30l/s if placed over the hob and 60l/s if place elsewhere ·Bath/shower - 15l/s with an additional 15 minute overrun (after the light is switched out) ·Toilet - 6l/s with overrun ·Utility room - 30l/s However, my builder told me that a kitchen and a utility room require mechanical ventilation even if they have openable windows. Whilst a bathroom and toilet (wc) only require mechanical ventilation if there is no openable window. This does not make sense to me. Can some kind person clarify what the actual reequipments are?