Wooden windows - are there any energetic advantages?

Again and again wooden windows are described as being particularly heat-insulating. To what extent that is correct, and whether wood windows actually have energetic advantages, read in detail in this post. In addition, which types of wood are particularly heat-insulating.

U-values ​​for windows

For windows, the total U-value is composed of the U-values ​​of the frame and the glazing. In addition, the size of the window and the length of the glass edge play a role in thermal insulation, as well as a few other factors

The thermal insulation of the frame is overall only a minor role. If you look at the Uw values ​​of a window, the window pane will certainly have the biggest influence on the overall insulation value. The better the U-value of the glazing, the better the overall U-value of the window.

Wooden windows - are there any energetic advantages?: advantages

Guide values ​​according to DIN

Since the U-values ​​of the frame play an already subordinate role for the overall U-value, as a rule no measurements are carried out, but general values ​​from DIN 4108-4 are used. These lump sums are certainly not applicable in many cases, but a costly measurement is usually not worth it.

The U-values ​​of metal and plastic windows from modern production today are on a test bench at a level that wood windows can no longer reach. Wooden window frames therefore have a higher U-value than modern, insulated plastic and metal windows. They are actually less thermally insulating than other types of windows.

Determining an exact U-value for the frame is difficult, and the results often vary widely.


Pine window frame, frame profile IV 68

  • Table result: frame 1.8 W / (m²K), glass 1.0 W / (m²K) window therefore 1.4
  • accurate calculation frame 1.3 W / (m²K) sideways, 1.7 W / (m²K) below, glass 1.0 W / (m²K) - window therefore 1.3
  • exact calculation by other method: frame and glass equal, window 1.2 UU

The example shows that according to the first calculation method (table) the window should not be installed according to the current provisions of the EnEV, but already according to the other two calculations.

Increased U-values ​​for individual types of wood

The standard values ​​for wooden windows, which are often used as a guideline for the U-value of the frame, only apply to conifers:

  • Fir (very rarely used in window construction)
  • Spruce and
  • pine

Other types of wood in the wooden window also lead to other U-values. This is especially true for wood species with increased bulk density:

  • Meranti additional 0.1 W / (m²K)
  • Larch additionally 0.1 W / (m²K)
  • Oak additionally 0,2 W / (m²K)


One can therefore say that wood window frames are fundamentally even worse insulated than modern metal or plastic windows.

By changing the thickness of the window profiles and reducing the profile widths, however, window frames can still be slightly optimized. For example, U-values ​​of 1.0 for the window frame are also possible for individual frames (window profile IV 110).

However, most wooden windows are inferior to well-insulated plastic or metal windows in the frame insulation values.

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