All the benefits at a glance 

Improved thermal insulation: The resulting ‘combined roof’ keeps the entire structure warm and dry during the heating season. As warm water vapour molecules do not condense, the problem of water vapour damaging the structure is eliminated. With initial U-values for the existing roof ranging from 1.2 to 0.45 W/(m²K) (watts per square metre per kelvin), this construction achieves a potential U-value of 0.1 W/(m²K), thereby providing an optimum balance of thermal insulation and comfort.

Flat roofs can quickly become heat traps in summer. The current thermal insulation requirements for lightweight roofs are insufficient. The problem of summer heat under a flat roof is only solved with a U-value of 0.1 W/(m²K), which keeps the interior roof cladding below 25 °C.

Insulating the roof improves the surface temperature in winter from 15 °C to 20 °C when the outside air temperature is –5 °C. If other parts of the house are also properly insulated, the room temperature drops only slightly at night, even when the heating is switched off.

Lower heating costs: Depending on the initial situation and the roof’s previous insulation standard, savings of up to 90 per cent – based on the roof area – can be achieved. The total saving in heating energy for a bungalow can be up to 35 per cent. 

Further benefits: 

The advantages of the ‘combination roof’

• The entire roof structure is retained, saving on building materials, labour and construction costs.
• The insulation – particularly when combined with a green roof – protects the roof membrane from the elements, extending its lifespan. Thanks to evaporative cooling, the microclimate is improved in summer (lower air temperatures).
• Moisture risks are eliminated, and the roof structure remains warm and dry during the heating season.
• The construction provides a very high level of thermal insulation, reducing heating costs.
• Summer heat under the roof is eliminated, and living comfort during the heating season is optimal.
• The investment pays for itself within a few years through energy savings and reduced emissions from the building’s heating system: in terms of costs, energy used in production and CO₂ emissions.
• The house remains habitable throughout the renovation.
• The quality of the new roof complies with the GEG (Building Energy Act) and is eligible for funding under the BEG.

Benefits for climate protection

• Environmental impact: The insulation pays for itself quickly and reduces CO₂ emissions.
• Preservation of building components: No demolition, lower energy consumption compared to new-build construction.
• Efficient energy use: An optimal U-value enables more efficient use of renewable energy. Fewer days of heating required, smaller heat pumps.

Additional benefits of a green roof

• Green roofs: Protect the roof membrane from UV rays, extend its service life and lower the surface temperature through evaporative cooling.
• Rainwater storage: Green roofs can store rainwater and help to positively influence the water balance during heavy rainfall events in towns and cities.
• Habitat for insects: Green roofs provide a habitat for insects and their natural predators, such as birds, in a similar way to urban greening and green facades.

Costs/Cost-effectiveness: As a rule of thumb, the payback period is often around 15 to 20 years. The greater the savings on heating costs and the lower the investment costs for insulation, the shorter the payback period tends to be. 

Funding: Upgrading to a ‘combined roof’ is eligible for funding for U-values of 0.1–0.14 W/(m²K); the eligible costs are reduced by 15–20 per cent through a government grant for individual measures (BAFA).

Can I install the insulation myself? No, insulating an inverted roof requires specialist knowledge and expertise, as it is a specific type of roof construction. As always, assistance is available. Ask the tradespeople!