Roof
roof pitch
Drempel
Flat roof
Upper floor slab
Solid ceiling
timber-beamed ceiling
Nail binder
Attic conversion
External wall
Façade
Partition joint in a house
cellar wall
Ground floor
cellar ceiling
Stairway to the cellar
Solid ceiling
Cap ceiling
Timber joist floor/cavity
Special components
Thirty per cent of the external walls of buildings in Germany (particularly in northern and western Germany) are of a double-skin construction. This means that there is an air gap 1.5 to 13 cm thick between the inner and outer masonry, or behind a clinker brick façade. As the air in these cavities moves and is connected to the outside air via openings and joints, a great deal of thermal energy escapes. The consequences are high heating costs, a risk of mould and reduced comfort.
The facing course of these buildings was fixed using tie blocks or, from around 1950, wire anchors. Particularly in older masonry, very little binder was often used in the mortar – the facing course can therefore become unstable and be at risk of collapsing.
Please note: To ensure that external insulation (such as an ETICS) applied to this type of cavity wall works properly, the air gap between the masonry layers must first be filled with blow-in insulation.
How can I find out if my building has a cavity?
1. With the aim of improving thermal insulation in the long term, qualified staff carry out an on-site inspection of the building’s condition. The cavity is examined using an endoscope, for which a few small holes, each 1 cm in diameter, are drilled into the external wall.
2. To locate any connections between the cavity and the outside or the interior, synthetic smoke is introduced into the cavity where necessary.
3. If the cladding is unstable or even at risk of collapse, core insulation using liquid polyurethane foam restores the structural integrity of the cladding. The PU foam is mixed on site and injected into the cavity via hoses.
The foam has a high adhesive strength that is effective over a wide area. The insulation, with a thermal resistance of 0.027 W/m²K (watts per square metre per kelvin), offers thermal protection that is a factor of 10 better than that provided by the air layer.
The joint is always filled completely with insulation material; this also represents the maximum insulation thickness.
All the benefits at a glance
Improved thermal insulation: The level of thermal insulation achievable depends on the joint width and the insulation material used. If the so-called thermal transmittance coefficient (U-value) of the external wall was previously approximately 1.6 W/m²K (watts per square metre per kelvin), it can be reduced to 0.39 W/m²K with a 5 cm joint width as a result of the insulation work.
This represents a thermal improvement in the external wall component of approximately 85 per cent.
Lower heating costs: The building’s heating costs are reduced by approximately 20 per cent.
Further benefits:
- Comfort is enhanced due to higher temperatures on the inside surfaces of the external walls
- Mould growth is prevented, as the inner surfaces of the external walls become warmer and therefore drier
- Draughts caused by openings and leaks in the wall (e.g. sockets, etc.) are eliminated
- CO₂ emissions are reduced
- The structural integrity of the cladding is restored
- The appearance of the façade is preserved (listed building status!)
- The procedure is minimally invasive
Costs/cost-effectiveness: Depending on the size of the building, its location and the thickness of the cavity, the cost of façade stabilisation is approximately €100–130 per m².
Funding: If the insulation material used has a lambda value ≤ 0.035 W/m²K, the retrofit core insulation is eligible for a 20 per cent tax relief or, under the BEG, the Federal Funding Scheme for Efficient Buildings (BEG), up to 20 per cent (as part of an individual renovation roadmap, iSFP) of the total costs in the form of an investment grant.
The BEG subsidy is administered by the Federal Office for Economic Affairs and Export Control (BAFA). The eligible investment amount is capped at 60,000 euros per calendar year and per residential unit, and at 600,000 euros per building. To receive the funding, you must engage a qualified energy adviser before work begins. Further information
Can I carry out the insulation myself? No, retrofitting core insulation with façade stabilisation requires specialist equipment and technical expertise, and must be carried out by specialist blow-in insulation contractors. However, you can offer to assist the contractor carrying out the work, for example by drilling and sealing the injection holes or by cleaning and tidying the building site; they will certainly be happy to accept your help and, in the best-case scenario, will offset this against the final price.