In the case of the building enclosures or envelopes, the energy demand of a building will be checked using two parameters: /p>

• The solar factor modified in the cavities (FH), which is the amount of heat exchanged with the exterior, measured in W/m2K.
• The cavity heat transfer (UH), also expressed in W/m2K, which indicates the amount of heat, divided by the area and by the temperature differences on each side of the building enclosure.
   

For the calculation of the cavity transfer figures (frame + glass) it is necessary to take the following into account: the climatic area where the town/city is located, the orientation of the façades, the percentage of cavities on the façade and the heat transfer of the wall UM.

Depending on the geographical location of the building, the CTE (Technical Building Code) establishes 5 climatic area depending on the climatic severity of the winter (A, B, C, D, E)and 4 areas depending on the climatic severity of the summer (1, 2, 3 and 4). The combination of both results in 12 climatic areas.

                                       Overall Heat Transfer Coefficient U-Value W/m2 K