Roof

In the middle of the last century, reinforced concrete ceilings began to become widespread. These solidly constructed ceilings offer poor thermal insulation. They cause significant heat loss, particularly when used as cellar ceilings, leading to unnecessarily high heating costs and reducing living comfort. They are characterised by a flat, level construction and are therefore well-suited for the use of panel insulation materials.

How is it insulated?

Depending on the condition of the ceiling to be insulated, a decision is made as to whether the insulation boards should be glued or fixed with wall plugs. If the substrate is load-bearing and suitable for gluing (i.e. free from paint and loose plaster), the gluing method can be used. If the substrate does not meet these requirements, the boards are fixed to the ceiling using dowels. This involves following a laying pattern with specified dowel points. It is common to find pipes laid ‘on the plaster’ on cellar ceilings. These remain in place and are encased by cut-outs in the insulation.

Basement ceiling insulation – helpful installation guidance from the Energy Saving Commissioner, plus a supplement regarding thermal bridges.

Important: As basement walls are constructed from solid bricks, sand-lime bricks or even concrete for structural reasons alone, and these materials act as significant thermal bridges, the walls should be insulated from above using insulation boards 50–60 cm thick. If this is not done, a large proportion of the ceiling insulation is virtually ineffective!

As with any insulation, the following applies: insulation boards must not be rear-ventilated, as this would severely limit or even eliminate their insulating effect. Care must be taken to ensure a joint-free and airtight installation.

Which insulation materials are suitable? If there is ample space (installation height) available, all insulation materials such as polystyrene, rock wool, etc. can be used. If this is not the case, high-performance insulation materials such as phenolic resin WLS 021 or PU WLS 023 (aluminium-laminated) are recommended. In boiler rooms and service corridors in rental housing, only rock wool boards may be used.

Insulation thickness

Polystyrene or rock wool panels should be at least 15 cm thick. If this is not possible, 8–10 cm thick phenolic resin panels or PU panels are a suitable alternative. The walls should also be insulated from above using the same panels.

All the benefits at a glance

Thermal insulation: If the U-value of the cellar ceiling was previously around 1.6 W/(m²K), it can be reduced to around 0.25 W/(m²K) through insulation measures. This represents a thermal improvement of approximately 85 per cent for the cellar ceiling.

Heating costs: The heating costs for a single-storey building (bungalow) can be reduced by up to 10 per cent.

Further benefits:

Comfort is enhanced due to higher temperatures on the ground floor (“warm feet”)
CO₂ emissions are reduced.
Heating energy consumption and heating costs are reduced
You can carry out this work yourself
Insulating the heating pipes, if this has not already been done, can be carried out at the same time. (This has been a legal requirement for many years)

Costs/cost-effectiveness: Depending on the level of difficulty, the work can cost up to €100 per m². Thermal insulation can be improved by up to 85 per cent. The work pays for itself in around 15 years.

Financial support: This measure is subsidised by the government at 15 per cent of the total costs via the BAFA (an energy consultant 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?) Unfortunately, there is no subsidy if you carry out the work yourself

Can I install the insulation myself? Yes.

Download document:

Fördermittel - Bundesförderung effiziente Gebäude .pdf