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
After the external walls, roofs and upper floor slabs are the largest surfaces through which valuable heating energy is lost. If the loft space under the roof is unoccupied and therefore unheated, insulating the roof is pointless, as it is far too expensive and the amount of heating energy that can be saved is always less than if, as described below, the ceiling is insulated. If the ceiling above the unheated loft consists of a concrete slab, its thermal performance can be significantly improved using simple methods and by laying insulation mats on top.
Insulation is installed on top of the concrete slab. An insulation thickness of at least 22 cm is recommended (for WLS 032: eligible for funding, sustainable). It is possible and advisable to install a sort of ‘walkway’ leading to the chimney for the chimney sweep. If ‘normally flammable’ insulation material (building material class B2) is used, the chimney must be clad with non-combustible insulation material to a thickness of at least 10 cm. Tip: You should consider whether the loft is to be used as a storage space or similar, or just part of it. Installing ‘accessible’ insulation involves considerably more work and is therefore at least twice as expensive. Tip: The loft access area should also be insulated.
Which insulation materials are suitable? In principle, any insulation material can be used to insulate the ceiling. However, for DIY ceiling insulation, mat-type insulation made from mineral or rock wool is particularly suitable; jute, hemp or flax mats are also an option. Loose-fill insulation can also be used. The use of board insulation of any kind is not recommended. (As the loft is often uneven and may contain cables, wooden beams, etc., it is more difficult to install board insulation without gaps. Furthermore, it is considerably more expensive than mat, loose-fill or blow-in insulation.
Costs, payback period, CO₂:
Insulating the upper floor slab has been a requirement for many years. A U-value of at least 0.24 W/m²K must be achieved (GEG). This corresponds to an insulation thickness of 12 cm when using standard commercial insulation materials (WLS 035 to 040). If the federal subsidy (BAFA, tax incentive) is claimed, a U-value of 0.14 W/m² must be achieved. This corresponds to an insulation thickness of 20 to 24 cm (depending on the insulation quality of the product used). Insulation thicknesses of up to 40 cm, on the other hand, are economical, sustainable and environmentally friendly.
All the benefits at a glance
Thermal insulation: If the U-value of the upper floor slab was previously approx. 1.3 W/(m²K), it can be reduced to approx. 0.14 W/(m²K) through insulation measures. This represents a thermal improvement of approximately 90 per cent for the upper floor slab.
Heating costs for a single-storey building can be reduced by up to 30 per cent. In multi-storey buildings, the percentage saving is lower, but the absolute energy saving for the entire building remains the same.
Summer heat protection: the temperature in rooms beneath uninsulated ceilings can reach up to 35°C in summer. Insulating the ceiling can reduce the temperature by up to 10°C (provided that solar heat gain through windows etc. is reduced).
Further benefits:
- Comfort is improved due to higher temperatures in the ceiling of the upper storey
- Summer heat protection is significantly improved
- CO₂ emissions are reduced.
- Heating energy consumption and heating costs are reduced
Costs/cost-effectiveness: 20 cm glass wool mats cost approx. €19, although an insulation thickness of at least 30 cm is recommended. In this case, the cost is €28 per m². The measure pays for itself in less than 2 years.
Subsidy: If you carry out the work yourself, the material costs (not the labour!) are only eligible for a subsidy if an energy adviser certifies the eligibility. An insulation thickness of at least 20 cm must then be achieved using an insulation material with a thermal conductivity of 0.32. This measure is subsidised by the government at 15 per cent of the total costs via the BAFA (an energy adviser is required in each case; an additional 5 per cent is available if an iSFP is drawn up). A subsidy via income tax under Section 35c of the Income Tax Act (EStG) is not available if you carry out the work yourself.
Can I install the insulation myself? Yes. However, blow-in insulation carried out by a specialist contractor is considerably quicker and eligible for a grant.
Historical note: As early as 1939, the following appeared in the journal ‘Bauwelt 1939’ in the essay ‘More Care in Construction’:
