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
Many older buildings have converted attics where the sloping roof sections (approximately 2–4 metres in length from the eaves to the upper floor slab) are either not insulated at all or are inadequately insulated. However, thermal insulation can be improved with little effort using the blow-in insulation method. This is particularly useful where a roof underlay is already in place. The cavity between the rafters should be at least 6–12 cm deep. The blow-in insulation method can initially serve as partial insulation, which is later supplemented by insulation installed either on top of or beneath the rafters.
From the loft, the cavity in the sloping roof is filled with insulation material without leaving any gaps. Only non-settling fibre insulation materials may be used for blow-in insulation; these interlock with one another during the blowing process and form a homogeneous, i.e. uniform, insulating layer. The work takes about one day for a detached house. The disruption to daily life caused by the work is limited solely to the stairwell. Ensure that the contractor carrying out the work holds a QM qualification. Only then can it be guaranteed that the work will be carried out correctly. This is because, with vapour-tight external cladding (mesh-reinforced membranes, timber cladding with bitumen waterproofing), condensation may form. Excessive condensation can lead to moisture damage or the leaching of flame retardants. For this reason, only capillary-active insulation materials (which can absorb and release water) such as cellulose or wood fibres should be used.
You can find specialist companies here
The thickness of the insulation is limited by the thickness of the rafters. A thickness of 15 cm is usually achieved.
All the benefits at a glance
Improved thermal insulation: If the so-called heat transfer coefficient (U-value) of the roof is 2 W/m²K (watts per square metre and Kelvin) before the insulation work, this can be improved to as low as 0.3 W/m²K. Thermal insulation is therefore up to seven times higher than before.
Lower heating costs: This measure can reduce the building’s heating costs by 10 per cent.
Further benefits:
- Draughts are minimised
- Comfort is improved due to higher temperatures on the inside of the external walls
- Mould growth is eliminated
- Summer heat protection is significantly improved
- CO₂ emissions are reduced
- The method is minimally invasive
Costs/cost-effectiveness: As the structure is already in place and no further work is required, this insulation method is extremely cost-effective: the cost is less than €20 per m².
Financial support: As the U-values achieved do not meet the specified minimum technical requirements, this measure is not eligible for government funding.
Can I install the insulation myself? No, blow-in insulation requires a blow-in machine. By helping out – for example, by feeding the insulation material into the machine – you may be able to reduce the costs. Please ask the specialist contractor about this!
