Understanding Condensation in Buildings
Condensation is one of the most misunderstood building problems. It is often misdiagnosed as rising damp or a roof leak, leading to ineffective and costly repairs.
What Causes Condensation?
Condensation occurs when warm, moisture-laden air meets a cold surface. The air cools, its capacity to hold moisture drops, and water vapour condenses into liquid on the surface.
Two Types of Condensation
Surface Condensation
This occurs on visible cold surfaces such as walls, windows and ceilings. It is the most recognisable form — appearing as water droplets or damp patches, often accompanied by mould growth.
Interstitial Condensation
This occurs within the building fabric — inside walls, roofs or insulation layers. It is invisible and far more damaging, as it can degrade insulation, corrode structural elements and promote timber decay over time.
Common Triggers
- Insufficient ventilation
- Inadequate insulation creating cold surfaces (thermal bridging)
- High internal humidity from cooking, drying clothes or occupancy
- Cold bridges at junctions and openings
Why Diagnosis Matters
Treating condensation as a 'leak' leads to failed repairs. The correct approach is to:
- Confirm whether the moisture source is condensation or water ingress
- Identify the driving mechanism (humidity, ventilation, thermal bridging)
- Recommend targeted remediation
A proper investigation uses moisture mapping, thermal imaging and building physics analysis to reach the right diagnosis.