Five times better heat protection thanks to new glass!

A gentle breeze can be quite refreshing at times. But if you feel a cool gust of wind around your nose even with the windows closed, then you shouldn't forget the windows when modernizing your home.

It's worth it, because in the last 30 years, the "window" has evolved from a thermal weak point in the building envelope to an effective form of thermal insulation. This progress can be measured specifically by the U-value, the heat transfer coefficient.

As the name suggests, this indicates how much energy is lost per square meter of window area. The lower the value, the better the window's thermal insulation (and the lower the loss of heating energy).

The Uw value is what matters

Of course, it's not just the glazing that matters, but also the frame and seals. Therefore, when choosing new windows, pay attention not only to the CE mark, which guarantees compliance with EU standards, but also to the Uw value (measured in W/(m²·K), which means watts per square meter and Kelvin). This is because only the Uw insulation value takes the window frame profile into account.

For comparison: Single-glazed windows installed before 1978 have a U-value of 5, while double-glazed windows have a U-value of 3 W/(m²K). Modern windows with double-pane thermal insulation glass and a U-value of 1.2 already meet the requirements of the German Energy Saving Ordinance (EnEV). This ordinance allows values ​​up to 1.3 – and up to 1.4 W/(m²K) for roof windows.

Story

The decisive breakthrough in the history of windows came in 1995. At that time, a wafer-thin layer of metal began to be inserted between the panes of conventional double glazing to reflect heat radiation. Additionally, the space between the panes was filled with noble gas instead of air, which reduces thermal conductivity – meaning less heat can escape.

The cost of new windows depends on their shape and thermal insulation rating. The "bargain" price is around €100 per square meter, but prices of €400 and more are also possible (don't forget to factor in the removal and disposal of the old windows!). For example, if you live in a detached house built in the 1970s with 150 square meters of living space, you can expect to save between €5 and €6 per square meter annually on heating costs.

Pay attention to the U-value of the exterior wall!

Replacing windows only makes sense in conjunction with facade insulation. Why? If the windows are better insulated than the exterior wall, the coldest zone shifts from the window pane to the inner surface of the exterior walls. To prevent damage from condensation and mold, the U-value of the exterior wall should therefore be somewhat lower (i.e., better) than the U-value of the windows.