Ventilation in buildings is a vital part of a healthy environment, managing the relative humidity and the risks that come from having too high Rh*, condensation and in the worst cases, mould growth.
The legislation assumes that replacing windows will eliminate some natural air infiltration and potentially, increase the Rh*.
Therefore, it is a legal requirement where technically feasible to fit background ventilation, normally in the window through the means of trickle ventilators.
* Rh – Relative Humidity
