Condensation is the most common cause of dampness in buildings, and the most commonly misdiagnosed.
How it happens
Air holds moisture in proportion to its temperature. When humid air meets a surface below its dew point, moisture condenses, on cold external walls, behind furniture, in unheated rooms, on single glazing and cold bridges. Persistent condensation supports mould growth, which affects both the building and the health of the people using it.
A whole-building problem
Condensation is a balance of moisture production, heating, ventilation and the thermal performance of the fabric. That is why treating it as "rising damp", or simply painting over mould, always fails. It is also why insulation improvements made in isolation can move the problem rather than cure it, cooling one part of the construction until condensation forms there instead.
How we investigate
We assess surface temperatures, monitor humidity and temperature over time where needed, and consider how the building is heated, ventilated and used. In unoccupied historic buildings, condensation on cold masonry can be severe, at Chepstow Castle, monitoring recorded 96% relative humidity in the Earl's Chamber before remedial works. The remedy follows the evidence: usually a considered combination of ventilation, heating, moisture management and targeted fabric improvements.
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