The U-value of a box window can only be improved consuming

The U-value of a box window is in most cases higher than that of modern single-pane windows with double or triple glazing. But since, for example, in older buildings and historically protected buildings an exchange is out of the question, the manufacturers and window manufacturers have developed designs that meet the requirements.

Example values ​​and classification

The currently valid Energy Saving Ordinance (EnEV) of 2014 sets the maximum U-value for windows at 1.4 W (m²K). In the case of a building stock with old so-called K-glazing, this U-value can be barely reached with old windows after modernization. The heat transfer coefficient and today's U-value was formerly called the K-value of the window.

Examples of standard values ​​for the U-values ​​of different window types are:

  • Old single-leaf window with simple glazing about 4.5 W (m²K)
  • Old single-leaf window with old K-value glazing about 2.7 W (m²K)
  • Old box window with simple glazing about 2.5 W (m²K)
  • Simple energy-saving window as a composite window about 1.8 W (m²K)
  • Simple window with double or triple glazing about 1.4 W (m²K)
  • Box window with insulating glazing of the inner window F and optimized sealing about 1.4 W (m²K)

Measures for improvement

In order to improve the U-value of a box window or to bring it into the required legal minimum frame or beyond for new products, the heat protection of the window must be optimized on several components of the overall construction:

  • The bond between frame and soffit must be sealed with window sealing tape
  • In the frame and the bond to the soffit thermal bridges must be interrupted
  • The inner window must have a milled sealing profile
  • Driving rain must be generated on the outer casement

Wooden windows achieve better U-values

In general, the U-value for wooden windows is lower than that of other materials. Box windows should only be constructed of wooden frames to take the favorable effect of the Uf value of the wooden frame and to combine them with modern insulating glazing.

Tips & Tricks

If you want to use new box windows, F, the top products can have U-values ​​up to 0.8W (m²K). Proportional to the decrease of the value, the price of box windows increases.

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