Triple Glazed windows have a very low U-Value (the importance of which we mention here) due to the use of a low emissivity coating and Argon gas. On a still night, the temperature of the outer glass surface can easily fall below the exterior air temperature or even its dew point temperature. Condensation occurs when the glass temperature falls below the dew point temperature but rest assured this is perfectly normal and a sign that your window is doing its job. This condensation will not evaporate until the glass is heated by wind, sunlight or heat transfer from inside your house. Our triple glazed windows will suffer external condensation, as they are very thermally efficient.