Short answer: exterior condensation on windows is usually normal and occurs when warm indoor air contacts a cold outer pane during colder weather. Details
- What causes it
- Temperature difference: When the inside of the house is warm and humid and the outside is cold, the outer surface of the window can become cold. Warm, moisture-laden indoor air meeting that cold surface can release water vapor as liquid droplets on the outer pane. This is condensation forming on a colder surface, not necessarily a defect.
* Outdoor humidity and weather: High outdoor humidity can contribute to visible moisture on the exterior surface, especially when the glass is well-insulated and the inside is warmer. This is more common in autumn/winter mornings or evenings.
* Window performance factors: External condensation does not automatically indicate a faulty seal; it can occur even with new, well-sealed windows. However, if you notice persistent fogging between panes or a drop in insulating performance, a seal or spacer issue may be present.
- When it’s likely harmless
- Typical in cool, damp conditions or mornings; is often a sign the window is performing to keep heat in. If condensation clears as outdoor conditions change, it’s usually not a problem.
- When to worry
- If condensation appears between the panes (between the two glass layers) or if there are persistent damp issues, it could indicate a failed seal or degraded glazing. In that case, a professional assessment is advised.
- Practical tips
- Improve room ventilation to reduce indoor humidity (e.g., use extractor fans, vent lids, or run a dehumidifier).
- If outdoor condensation is frequent, consider checking window installation quality and ensuring proper drainage and sealing at edges. A professional can confirm if the exterior condensation is purely weather-related or if a retrofit or replacement is needed.
If you’d like, provide your climate details (season, typical outdoor humidity, whether the condensation is on the outer surface only, and if you notice any internal condensation). That will help tailor the explanation to your situation.
