Insulate window frames professionally according to EnEV


In earlier times, insulating the window frames was solely in the hands of the building owners, who valued more or less comfort and energy consumption. Since the European Energy Saving Ordinance (EnEV) came into force, the heat transfer values ​​must meet and be documented as minimum requirements.

Sealing strips and joint tapes

In order to achieve optimized thermal insulation for windows by insulating the window frames, professional window construction companies today all use a similar installation technique.

Before inserting the window frame, a window sealing tape is applied, which is used in the form of self-adhesive plaster sealing strips or as waterstops. The glued on the outer and inner edges sealing tapes are glued to the masonry after foaming the space between the window frame and masonry or window reveal.

Prevent heat and cold bridges

While previously dowelled fastening screws or metal retaining anchors were used to fasten the frame, today special window screws without dowels are used to avoid any possibility of heat or cold bridging. Metal frames must have a heat-insulating window core and metal sills must not touch the metal window frame directly.

In addition, the window reveal can be insulated inside. To make an optimal connection between window sealing tape and masonry, a smooth line of the window reveal is required for example in brick buildings.

Heat transfer coefficient

When insulating the window frames, it is necessary to follow the guidelines of the EnEV which prescribe individual and total values ​​of the heat transfer coefficient. The values ​​formerly called K-value of the window are known today as U-values.

The U-value of an entire window consists of three values:

  • Uf value of the window frame
  • Ug value of the glazing
  • U-value of the window

The U-value of the window is a mean of Uf and Ug values, dividing the Uf value into lateral and bottom measurements. Isolating requires the U-value of the window frame to be at least 1.3. The lower the value, the better the insulation and frame construction. By a professional and optimized insulation of the window frames, the U-value of the entire window can be influenced up to fifty percent.

Tips & Tricks

If you have professional insulation provided by a qualified RAL-certified company, you can apply for funding from the Kreditanstalt für Wiederaufbau (KfW).


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