Window replacement ventilation

Part F

Provision should be made to ensure that appropriate ventilation is maintained and is made no worse as a result of a replacement glazing installation. The Building Regulations require that adequate ventilation is provided for people in the building and this should be considered when deciding on the size of opening lights in the replacement windows. For most rooms, one or more opening windows totalling 5% of the floor area, with background "trickle" vents totalling 8000mm2 will be adequate. For kitchens, utility rooms and bathrooms an extract fan is also normally required. In some cases the existing windows may contain a permanent vent to supply combustion air to a heating appliance, although this is now rare. If this is the case however you should ensure that either the replacement window contains a similar permanent vent, or that some other means of providing the required ventilation is installed at the same time.

All buildings

Replacement windows should have sufficient openings to ensure that the area of ventilation is not less than that provided by the existing windows or the current minimum standard, which ever is the lesser.

Typically accepted standard - current requirements

Provision should generally meet the requirements appropriate to a new property:

Rapid

Area equivalent to 1/20th floor area of the room served

Dwellings

Habitable rooms @ 8000 mm² - Kitchens, Bathrooms & WC’s @ 4000 mm²

Background (trickle) - non-domestic

Occupiable rooms up to 10 m² floor area @ 4000 mm² -- Occupiable rooms over 10 m² floor area @ 400 mm²/m² floor area -- Kitchens, Bathrooms & WC’s @ 4000 mm²