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 not heated, insulating the roof is pointless, as it is far too expensive and the heating energy that can be saved is less than if, as described below, the ceiling is insulated. Timber-beam ceilings – also known as purlin-beam structures – often have a hollow layer or are fitted with only thin layers of insulation material. Insulating the top side of these hollow-layer ceilings is thermally almost ineffective due to rear ventilation effects (the air flows horizontally from one roof surface to the next beneath the floorboards).
First of all, a check is carried out to determine whether there is a hollow layer. To do this, either a floorboard is lifted up or a hole is drilled. A folding rule or a stiff piece of wire is inserted into the hole to determine the depth of the hollow layer.
If the cavity is thicker than 3 cm, specialist blow-in insulation contractors will either create small openings in the floorboards or – even more simply – remove a floorboard. A blow-in hose is fed through these openings, and the cavity is filled with blow-in insulation through it. The process is carried out in each cavity; within a few hours, the ceiling is completely filled with insulation and insulated. See below
In principle, the upper floor slab can be insulated from above using any type of insulation material. The following section lists the most cost-effective insulation methods, which are technically and environmentally sound.
As an insulation thickness of 14 cm is not sustainable and is not eligible for government funding, it is advisable – whilst the blow-in team are already on site – to apply additional blown-in insulation of up to 20 cm in thickness (making a total of up to 34 cm). Free-flowing blow-in insulation materials such as perlite, SLS20 or polystyrene beads are not suitable. As an alternative to blow-in insulation, insulation mats can also be laid by the homeowner. Unfortunately, however, this is not eligible for a grant.
If the ceiling is to be ‘accessible’, e.g. as a dry floor, or for storing furniture and similar items, the insulation structure can also be constructed using wood-based panels on the upper side. Various joist support systems available on the market can be used for this purpose.
Important: Insulation on the upper side, regardless of the type of insulation material used, is thermally ineffective unless the cavity is completely filled with blow-in insulation.
You can find qualified tradespeople here.
Furthermore: As a timber-beamed ceiling is generally relatively vapour-permeable, whereas a top covering (whether timber floorboards or wood-based panels) is not, there is a risk of condensation forming beneath the wood-based panels and moisture penetrating the structure. In this case, a vapour barrier should be installed directly onto the timber floorboards, bonded in an airtight manner. This eliminates the risk of condensation.
The cavity in the ceiling structure is filled completely. This usually results in an insulation thickness of 12 to 16 cm. The additional insulation layer should be up to 20 cm thick.
All the benefits at a glance
Thermal insulation: If the U-value of the upper floor slab was previously around 1.3 W/(m²K), it can be reduced to around 0.14 W/(m²K) through insulation measures. This represents a thermal improvement of approximately 90 per cent for the ‘upper floor slab’ component.
Summer thermal insulation: 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 gain through windows etc. is prevented).
Heating costs for a single-storey building can be reduced by up to 20 per cent. For multi-storey buildings, the percentage saving is lower.
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: Depending on the level of difficulty, the total cost of the project can be up to €70 per m². Thermal insulation can be improved by up to 90 per cent. The project pays for itself in under 10 years.
Financial support: This project 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) or via the tax incentive (Section 35c of the Income Tax Act) – in this case, a 20 per cent tax relief (link?)
Can I insulate the property myself? No, you need blow-in insulation equipment. However, the costs can be significantly reduced by helping out (setting up the scaffolding on site, feeding the insulation material into the blow-in machine, cleaning up and dismantling the scaffolding, and also constructing the ‘accessible structure’). Ask a specialist contractor!
DIY method: Insulation by rolling out mat-type insulation materials. However, this is not eligible for government funding.
Historical note: As early as 1939, the following appeared in the journal “Bauwelt 1939” in the essay “More Care in Construction”:
