Solid ceiling

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 heating energy that can be saved is less than if, as described below, the ceiling is insulated. A tool for determining the difference between roof and ceiling insulation. If the ceiling above the unheated loft consists of a concrete slab, its thermal performance can be significantly improved using simple methods and blow-in insulation.

How is it insulated?

No insulation material can withstand permanent loading; all insulation materials must therefore be protected by a wood-based panel on the upper surface. In principle, any type of insulation material can be used. The most cost-effective option is to construct a substructure using ‘DämmRaum’ elements. This is then covered on top with a wood-based panel. The resulting cavity can then be filled with blow-in insulation. If cellulose blow-in insulation or another ‘normally flammable’ insulation material (building material class B2) is used, the chimney must be clad with non-combustible insulation to a thickness of at least 10 cm. A vapour control layer or vapour barrier is not required for this method. However, any penetrations (pipes, cables) should be sealed airtight.

Tip: The loft access area should also be insulated.

Which insulation materials are suitable? The upper floor slab can be insulated with any insulation material. However, it is advisable to use blow-in insulation materials, as these 1. offer the best value for money, 2. can be installed completely without joints or off-cuts, and 3. the insulation can be completed in just a few hours.

Insulation thickness

Insulation of 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 14 to 16 cm when using standard 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 25 to 28 cm. Insulation thicknesses of up to 40 cm, however, are economical, sustainable and environmentally friendly. Temporary

insulation: If the roof needs to be insulated as part of a subsequent loft conversion, the blow-in insulation can simply be removed from the ceiling (where it is then no longer required) and incorporated into the roof insulation to be installed at that time. See the attached PDF.

“If you’re going to do it, do it properly”

All the benefits at a glance

Thermal insulation in winter: 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 in the upper floor slab of around 90 per cent.

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 30 per cent. In multi-storey buildings, the percentage reduction is lower, but the absolute energy saving for the entire building remains the same.

Further benefits:

Comfort is enhanced due to higher temperatures in the upper-storey ceiling
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 and the size of the property, the work can cost up to €75 per m². Thermal insulation can be improved by up to 95% (depending on the initial situation). The work pays for itself in less than 8 years.

What insulation thickness offers the best value for money?

Financial support: 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) or via tax relief (Section 35c of the Income Tax Act (EstG)) – in this case, a 20 per cent tax relief. A U-value of no more than 0.14 W/m²K must be achieved. With ‘standard’ insulation materials, this corresponds to an insulation thickness of at least 26 cm.

Can I install the insulation myself? Not the blow-in insulation – you need specialised blow-in equipment. However, you can install the substructure and the wood-based panels yourself. Furthermore, the cost of the blow-in insulation can be reduced by helping out (setting up scaffolding on site, feeding the insulation material into the blow-in machine, cleaning up and dismantling the scaffolding, and, if necessary, constructing a walkway for the chimney sweep). Ask a specialist contractor!

It is also possible to insulate the roof structure yourself using board insulation (which must also be covered with wood-based panels to make it accessible), but this is considerably more labour-intensive and expensive. In this case, only the material costs are eligible for a grant if they exceed €2,000. This must also be certified by an energy adviser.

Historical background:

As early as 1939, the following appeared in *Bauwelt 1939: Care in Construction*: