Private rented property standards guidance

There must be sufficient and appropriate means of ventilation across the whole property to deal with moisture generated by normal domestic activities without the need to open windows. 

Opening windows to ventilate a room can lead to unintended consequences, especially in cold weather.

• Temperature drop: opening windows allows cold air to enter, reducing the room temperature and potentially chilling the building fabric below the dew point creating condensation
• Condensation risk: As the temperature drops, the air's capacity to hold water vapour decreases. For example, air at 20°C can hold 15 grams of water vapour per kilogram, but at 5°C, it can only hold five grams. The excess moisture (10 grams) condenses quickly, leading to condensation. This condensation often occurs in bathrooms when windows are opened after a shower, giving the false impression that steam (moisture) has exited the window.
• Heat loss: Opening windows in cold weather also results in significant heat loss, increasing energy costs.

Managing ventilation and humidity effectively is crucial to avoid these issues.

To achieve this the following methods should be utilised.

• Windows that are double glazed should be provided with trickle ventilation
• All bathrooms should have mechanical ventilation installed (see bathroom standard)
• All kitchens should have mechanical ventilation installed (see kitchen standard)
• Installation of a PIV (Positive Input Ventilation)
• Single room heat recovery fans
• dMEV continuous running extractor fan with Humidistat. These are always on and work by sensing if there an increase in humidity and then run more to extract and change the air.

Where council officers assess there is an issue with damp, condensation, and moisture levels they may insist on the installation of mechanical extraction to deal with this using the methods described above.