Condensation and Ventilation

If you don't have sufficient ventilation in your flat you may start to suffer from condensation. This can be tackled by improving ventilation.

Kitchen and bathroom ventilation

The recommended ventilation for a kitchen are to have an extractor fan above a cooker (such as a cooker hood) capable of extracting 30 litres a second or an extractor fan in the room capable of extracting 60 litres a second. Unless the ductwork is built in, this usually results in coring a hole through an external stone wall which is 100mm diameter to allow the air to be extracted.  It is better if the core drill is done from the outside, if done from the inside it will likely damage the stonework. Alternatively passive stack systems can be installed to naturally draw up an extract duct. This can be fitted on the top floor flats as a duct can be taken through the ceiling and through the roof finish (whether it is slate of tile). Pipework which penetrate the roof can be flashed with a special collar and flashing called a ‘slate piece’.

Bathroom ventilation will be formed in the same way having an extract rate of 15 litres a second (or passive stack vents). If you just have a toilet then an opening window is sufficient provided that the opening area of the window is at least 1/30th of the toilet floor area.

Room to room ventilation

It can be important to ensure there is ventilation room to room, rather than sealing up each room. This may be provided by having a vent gap or fanlight above the door. 

Mechanical Heat Recovery Units

Mechanical Heat Recovery units are now commonly installed in newbuilt flats. They can be triggered by a humidistat and commonly work to ventilate and recover heat from the whole house. Fans and filters from the units need to be serviced and replaced so it is best that the units are sited in the close if possible. Also, as some units can make a background noise, residents are inclined to switch off the units which can lead to condensation forming.