Where the original windows were fitted with trickle ventilators the replacement windows should include them and they should be sized as below,
Where the original windows were not fitted with trickle ventilators and the room is not ventilated adequately by other installed provisions, it would be good practice to fit trickle ventilators.
In all cases where controllable trickle ventilators are to be fitted, the new ventilation opening should not be smaller than was originally provided.
Where there was no ventilation opening, or where the size of the original ventilation opening is not known, use these minimum sizes.
habitable rooms – 5000 mm2 EQA
kitchen, utility room and bathroom (with or without WC) – 2500 mm2
Buildings other than dwellings
Occupiable rooms: for floor areas up to 10 m2 – 2500 mm2 EQA; greater than 10 m2 – at the rate of 250 mm2 EQA per m2 of floor area
Kitchens (domestic type) – 2500 mm2 EQA
Bathrooms and shower rooms – 2500 mm2 EQA per bath or shower
Sanitary accommodation– 2500 mm2 EQA per WC.
Adding a habitable room to an existing dwelling
The adjoining rooms could be ventilated by one of the following options.
Background ventilators could be used.
The additional room is connected to an existing habitable room which now has no windows opening to outside, follow the new dwelling guidance. If the new room is connected to an existing habitable room which still has windows opening to outside but with a total background ventilator EQA less than 5000 mm2, follow the new dwelling guidance.
If the new room is connected to an existing habitable room which has windows opening to outside and with a total background ventilator EQA of at least 5000 mm2, background ventilators of at least 8000 mm2 EQA between the two rooms and background ventilators of at least 8000 mm2
EQA between the new room and outside.
Addition of a wet room to an existing dwelling
Whole building and extract ventilation can be provided by an intermittent extract and a background ventilator of at least 2500 mm2 EQA