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The U value characterises the heat transmission of an element or its components (wall, roof, window, profiles, glass, etc.). Following the introduction of the Energy Saving Regulations (EnEV) the U value must be determined in accordance with European harmonised standards.
As the system provider for window and frame profiles we are obliged to specify the Uf values for profiles and profile combinations.
This is done on the basis of measurements in accordance with DIN EN 12412-2 or calculations in accordance with DIN EN ISO 10077-2. In order not to have to measure or calculate every single possible profile combination in a system, the ift Guidelines WA-01/1 and WA-03/1 specify procedures for defining system-dependent characteristic curves from which Uf values can be derived for window profiles from the ratio of the height of the insulation zone(s) bt to the total elevation width B and for façade profiles from the room-side depth of the profiles If. These characteristic curves are based either on official test reports from ift Rosenheim or on our own calculations in conformity with the standard.
You can use the following Excel worksheets for the exact calculation of the U value: