Why Winter Worsens Condensation
Warm air can hold more moisture than damp air. As air is cooled, its relative humidity increases – and water in the air turns into condensation (the temperature at which this occurs is known as the’ dew point’). This is why condensation often appears first on cold surfaces such as pipes, single-glazed windows and cold, often north-facing walls.
In the winter, the external air temperature is more likely to be low, meaning external walls and windows are cold. Cold air enters the building, is warmed and takes up moisture. When it then comes into contact with cold surfaces, it’s cooled below its dew point which creates condensation as the excess moisture is released.
It’s easy to have good ‘damp proof hygiene’ in warm weather – for example, by keeping windows open to allow air flow through your home, and drying clothes outdoors. However, as the weather worsens, it can be tempting to close all the windows – which may keep you warm but can also encourage damp. Other sources of damp can include paraffin and unventilated gas heaters, cooking, clothes washing and drying, bathing, washing dishes and inhabitants (one person breathes out around ½ litre of water vapour per day. The average family produces 7-14 litres of water per day through general day-to-day tasks.)
Signs you may have a condensation problem include water droplets on windows and walls, peeling paint and the appearance of moulds on wallpaper and paintwork, stained curtains and decaying window frames. Condensation can also occur under suspended floors, which can increase the risk of dry rot. This is best dealt with by ensuring good sub-floor ventilation including installing extra air bricks if required. If the ground is particularly damp, fitting a damp proof membrane on the soil oversite will also help.
Solving the Problem
While mould is unlikely to occur in a building if relative humidity is maintained below 70%, heating the air alone is unlikely to be a practical solution (not least due to the cost). Instead, you need to lower moisture levels as well as eliminating cold surfaces.
Improved heating and ventilation teamed with specific action for particularly cold spots will usually lead to significant improvements. A modest but constant background heat is preferable to intermittent heating as it helps the fabric of the building maintain a higher ambient temperature.
If you have an open fire or a fixed gas fire, a certain amount of natural ventilation will occur. Should additional ventilation be provided, it’s important that this is not blocked off.
Particularly cold internal walls can be insulated with foam lining paper or polystyrene tiles. However, you may need a vapour barrier on the ‘warm’ side of the insulation to prevent condensation occurring behind it.
Exterior walls can be treated with an external treatment including a masonry water repellent, such as Stormdry. This will reduce loss of heat from absorbed water evaporating. Using this type of treatment on solid walls and cavity wall insulation in cavity walls will help protect against interstitial condensation.
Installing an extractor fan in kitchens and/or bathrooms will help carry moisture-laden air away from the two areas most responsible for condensation without costing a fortune. Some extractor fans include a humidistat, controlling the operation of the fan within certain humidity limits. A good example is the Kair single room heat recovery ventilator.
This winter, be extra vigilant about ensuring your lifestyle isn’t encouraging any damp. It’s also worth checking you’ve prepared your home for the cooler weather – see our article on how you can stop winter from harming your home with a simple checklist of tasks.