Inadequate airtightness and its consequences

Financial + environmental / Heat losses

Heizung gross

Building envelope unsealed: High heating costs

Even very small leaks in the vapour retarder layer – such as those that arise due to faulty adhesion between membrane overlaps or joints – have far-reaching consequences. This type of weakness has the same effect as a continuous gap between the window frame and the walls – and of course nobody would tolerate such a gap!
Accordingly, gaps in the vapour retarder should be given the same attention.

Heizung klein

Sealed building envelope: Low costs and living comfort

The higher heating costs caused by faulty seals lead to reduced cost-effectiveness of the thermal insulation for the building owner. A study by the Institute for Building Physics in Stuttgart (D) has shown that the U-value of a thermal insulation structure is reduced by a factor of 4.8. ¹⁾

When applied to a practical case, this means that the same amount of energy is required for heating a house with a living space of 80 m² (96 yd²) where airtightness leaks are present as would be required for an airtight house with a floor area of approx. 400 m² (480 yd²).

The uncontrolled entry of air can also have a negative impact on the indoor environment, e.g. due to draughts, excessively dry indoor air in wintertime, or fast, strong heating-up in summertime.

Only a gap-free thermal insulation structure provides the full insulation value

According to a survey in the year 2000, buildings in Central Europe consume 22 l of oil/m² (220 kWh/m²) of living space for room heating on average; a passive house requires only 1 l, while a 3-litre house uses 3 l of oil/m², as the name suggests – assuming that the airtightness is perfect. Gaps in the airtightness layer of buildings lead to an increase in the energy requirement per square metre of living space.


¹)
The Institute for Building Physics in Stuttgart (D) has studied a 1 x 1 m sized structure with a thermal insulation thickness of 14 cm.
With a joint-free, airtight design, the previously calculated thermal performance of 0.30 W/(m²·K) was confirmed. However, if the same structure features only a 1 mm wide gap in the airproofing layer, the U-value deteriorates to 1.44 W/(m²·K). This means almost 5 times more heat is lost than with the airtight construction.