# What Is Condensation in Buildings?
**Condensation is the process by which water vapor in the air turns into liquid water when it comes into contact with a surface that is at or below the dew point temperature. In buildings, this phenomenon is a common cause of moisture damage, mold growth, and deterioration of materials.**
## How condensation occurs
Warm air can hold more moisture than cold air. When warm, humid indoor air meets a cold surface such as a window, exterior wall, or uninsulated pipe, the air cools rapidly. Once it reaches the dew point, the excess moisture is released as water droplets on the surface.
## Types of condensation in construction
– **Surface condensation** — Visible water droplets forming on windows, walls, or ceilings. This is the most recognizable form and often leads to mold growth.
– **Interstitial condensation** — Moisture forming within the building envelope, such as inside walls or roof structures. This hidden form is particularly dangerous because it can cause structural decay before becoming visible.
## Common causes
– Insufficient ventilation in kitchens, bathrooms, and bedrooms
– Poor or missing insulation creating cold bridges
– High indoor humidity from cooking, showering, or drying laundry indoors
– Single-glazed or poorly sealed windows
– Temperature differences between inside and outside
## Prevention methods
– **Adequate ventilation** — Mechanical or natural ventilation removes excess moisture from indoor spaces.
– **Proper insulation** — Continuous insulation eliminates cold bridges where condensation would form.
– **Vapor barriers** — Installed on the warm side of insulation to prevent moisture from migrating into the building envelope.
– **Double or triple glazing** — Raises the interior surface temperature of windows above the dew point.
– **Humidity control** — Extractor fans and dehumidifiers reduce indoor moisture levels.
## Related terms
– Dew point
– Vapor barrier
– Thermal bridge
– Relative humidity
– Interstitial condensation
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