Passive house flat roof window: The technical details

Comfort and technology

The intelligent use of highly efficient materials limits the minimum surface temperature on the inside of glass structures, thus preventing condensate and mould formation.

Mould grows on surfaces at a relative humidity of just 80 per cent or higher. When the indoor temperature is 20°C and relative humidity is 50 per cent (standard conditions), this corresponds to a surface temperature of 12.6 °C.

Such data is used to calculate the fRsi value, a coefficient which indicates the likelihood of mould growth. If this value is less than 0.7, there is a risk of mould forming.

In CI System Glass Element FEenergysave the fRsi value is a stable 0.73, thus corresponding to a minimum surface temperature of 13.3 ℃, an ideal value to ensure comfort and save energy.


Energy efficiency

Uf value






f Rsi=0.25


Lower surface0.61116.40.0290.73
Side/upper surface0.61116.40.0290.73