Moisture is present in old buildings not just from the activities of occupants, but also the fabric as it ‘breathes’. Historically, generous ventilation helped this escape via open fires, and loose-fitting doors and windows. The balance of the internal environment can easily be upset, though, increasing the condensation risk. This may occur when more moisture is produced – often from cooking, washing or the use of flueless bottled gas stoves and heaters. It also can happen where ventilation is reduced by double-glazing, over-zealous draughtproofing or blocking flues and air bricks.  Similarly, condensation forms where walls are cement-rendered externally, or insulated with a vapour barrier internally, compromising their ‘breathability’. Additionally, cold spots from gaps in insulation are conducive to condensation, as are walls or floors of high thermal mass when heated up suddenly.

Simple lifestyle changes can produce dramatic improvements at little or no expense:

• Ideally, generate less moisture. Place lids on pans while cooking, dry clothes outdoors, close kitchen and bathroom doors when in use and vent tumble driers to the outside if not of the condenser type.
• Improving ventilation to the exterior can also help. Even when it feels damp outside in winter, the lower vapour pressure will tend to draw out moisture. Open windows and avoid draught-proofing those in kitchens and bathrooms. Ensure that lofts, floor voids and redundant chimneys are well ventilated and avoid foam treatments on the underside of roofs that can cause serious timber decay.
• Increased heating can maintain surfaces above dewpoint, especially if run constantly at a low level rather than intermittently. Lagging cold pipes may prevent surface condensation, as can improving insulation levels (taking care not to cause interstitial condensation instead). The use of ‘hygroscopic’ materials that temporarily store excess moisture, such as sheep’s wool, can help avert condensation.