Minimum
England
Background ventilator equivalent area
8000 mm² equivalent area to habitable rooms; 4000 mm² to kitchens, utility rooms and bathrooms
Dwelling with background ventilators, including window replacement work
The background (trickle) ventilation provided to rooms in a dwelling.
Basis in regulation
How to check it on site
Check the ventilator equivalent area printed on the product data against the window schedule room by room — not the physical slot size.
Common failure
Ventilators specified by slot length rather than equivalent area, and units delivered without ventilators to habitable rooms.
Effective from 20 August 2026. Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.