There are cavities ‘hidden’ in almost every part of a building. There are more than 2.5 billion m² of cavities hidden in German buildings. 

They can be found in:

• external walls (double-shell construction, also common in high-rise buildings with concrete façades)
• in fitted-out, uninsulated sloping roof spaces/upper floor ceilings (timber-beamed ceilings), uninsulated wall plates/knee walls
• floors (timber floors on joists) between the basement and the ground floor
• flat roofs (bungalows, multi-storey residential buildings, high-rise blocks)
• also between semi-detached or terraced houses

External insulation (on the ‘cold side’) of these structural elements is virtually ineffective, or its insulating effect is severely limited, as the cavities are almost always ventilated and in contact with the outside air.

If the building elements are to be insulated, the cavities must first be filled with suitable insulation materials using the blow-in insulation method. Only then can additional insulation be applied ‘on the cold side’, which can then be made correspondingly thinner. You can find qualified and experienced contractors through the FVED e.V. 

Note: There is no such thing as a ‘stationary’ layer of air!