Quality assurance of air sealing in existing buildings
Why is air sealing necessary?
Until the 1990s, there were no set limits for the airtightness of buildings. As a result, older, unrenovated buildings are often relatively leaky compared to modern new buildings. However, successful energy renovation requires an improvement in airtightness. If a building has leaks, warm indoor air can escape uncontrollably, leading to heat loss and potential structural damage due to condensation.
When analyzing old buildings, it is useful to carry out an airtightness measurement (blower door test) to locate leaks. This measurement shows which areas are airtight and which places (usually connections and penetrations) need to be sealed. The measurement also provides an initial value for airtightness, which serves as a basis for determining the necessary measures required to achieve a planned target value. This is particularly important when limit values must be adhered to, for example when installing a ventilation system or when applying for funding.
Useful measurement times for quality assurance are:
- Before renovation: to locate leaks and determine measures
- During the renovation: for the monitoring of the work carried out during the construction, as long as the
Airtight layer is still accessible to make any necessary improvements - After renovation: as final measurement and for verification
Measurement before renovation (leak detection)
The danger of a leak depends not so much on its size but on its location in the building. Warm air rises (thermal buoyancy) and draws cold air from the lower areas. In the upper part of the building, components such as the ceiling or roof are at risk from convection moisture even in the case of small leaks.
Typical leaks in the attic
- Connections to the masonry
- Window connections in the gable or dormer
- Wooden beam ceiling to the attic
- Interior walls made of perforated bricks that integrate into the ceiling
It is not enough to achieve an airtight seal in the surface. The leaks in the connections (marked) must be repaired.
Heat losses
Joints in the airtightness layer of buildings can cause a significant proportion of the total heat demand of the building.
How much heat can be lost? A study by the Institute for Building Physics (Stuttgart) found that the U-value of a component can deteriorate by more than four times due to a 1 mm wide joint.
Moisture ingress through convection
Uncontrolled moisture ingress into the structure through warm air flow (convection) has serious consequences. Warm room air contains a lot of moisture. If the warm, humid room air flows into the cold outer areas of the exterior components in winter, the moisture condenses in the structure and can cause damage.
The penetration of convection moisture is particularly problematic in the case of a roof with waterproofing (flat roof). Due to the waterproofing, the component cannot dry out on the outside.
Conclusion: An energy-efficient renovation can only be successful if the air sealing is also improved.