Why energy retrofits are becoming increasingly important
Energy retrofits of properties have long ceased to be a voluntary commitment for particularly environmentally conscious owners. With the Building Energy Act (GEG), the EU targets for climate neutrality by 2050 and rising CO₂ pricing, the energy efficiency and CO₂ emissions of buildings are increasingly coming into the focus of legislation, lenders and buyers. Owners who do not act today risk significant value losses tomorrow. "Stranded assets" – properties that can no longer be sold or financed due to poor energy efficiency – are no longer a theoretical threat but already a reality in some segments.
This guide gives you a structured overview of the most important measures, the economic evaluation, the funding landscape and the legal framework for energy retrofits.
Legal foundations: What owners need to know
The Building Energy Act (GEG)
The Building Energy Act regulates the energy requirements for buildings during construction, modification and use. The most important requirements for existing properties:
- Heating obligation: When an old oil or gas heating system fails, it must be replaced by a system-integrated heating system – usually a heat pump, provided this is technically feasible.
- Individual measures: When replacing building components (e.g. windows, roof, facade), the minimum energy requirements must be met.
- Full retrofit: If more than 25 % of the heat-transmitting envelope surface is renovated, the requirement for a "contractually compliant, lowest-energy building" applies – i.e. approximately new-build standard.
The energy performance certificate
Since 1 May 2025, the energy performance certificate has been mandatory for sale or rental. The consumption certificate (consumption-based) is no longer sufficient; instead, a demand certificate (significantly more consumption-based) will become the standard in future. Owners should check early on which energy performance certificate they need and what energy rating their property currently has – this is an essential factor for marketability and purchase price.
Which retrofit measures make economic sense
Not every retrofit pays off. The profitability depends on energy prices, the property and its use. This sequence has proven itself in practice:
1. Replacing the heating system – the greatest lever
Replacing an old oil or gas floor-standing boiler with a heat pump is in most cases the most economically sensible individual measure. A heat pump reduces CO₂ emissions by up to 60 % and heating costs by 30 to 50 %, depending on the building and heat source. Prerequisite: the flow temperature of the heating system should be as low as possible – this usually requires large radiators or underfloor heating.
2. Insulating the building envelope
Insulating the roof, facade and basement ceiling is the second measure that significantly reduces consumption. The top floor and windows in particular are the biggest thermal bridges in older buildings. Facade insulation is expensive, but economically sensible if the facade is being renovated at the same time.
3. Replacing windows
Replacing single-glazed windows with modern double or triple glazing significantly reduces heat loss through windows. For listed buildings or windows worth preserving, internal shutters or composite windows are an alternative.
4. Ventilation system with heat recovery
In airtight buildings, a ventilation system with heat recovery can reduce ventilation heat loss by up to 80 %. However, the system involves investment costs starting from 8,000 euros and is only economically viable if the building's airtightness is improved at the same time.
Using subsidies correctly
The federal government, the KfW (Kreditanstalt für Wiederaufbau) and the federal states offer numerous subsidy programmes for energy retrofits. The most important:
KfW funding
- KfW 261: Grant for individual measures (e.g. heating, insulation, windows). Up to 20 % of eligible costs, depending on the energy standard and income.
- KfW 262: Loan with repayment bonus for comprehensive retrofits to the efficiency house standard.
BEG (Federal Funding for Efficient Buildings)
The Federal Funding for Efficient Buildings (BEG) bundles funding for heating systems (BEG EM) and buildings (BEG WG). The application must be submitted before the start of measures – retrospective applications are not approved.
Regional funding in NRW
The state of North Rhine-Westphalia offers additional funding programmes, e.g. for insulating existing buildings or installing photovoltaic systems. The city of Mülheim an der Ruhr also has its own funding programmes for energy measures.
Costs and profitability: a sample calculation
For a 1960s apartment building with 6 residential units (approx. 500 m² living space) in Mülheim an der Ruhr, the sample calculation could look like this:
| Measure | Investment | Annual energy savings | Payback period | |---|---|---|---| | Heat pump (instead of gas boiler) | €80,000 | €4,500 | 18 years | | Roof and facade insulation | €70,000 | €3,000 | 23 years | | Window replacement | €35,000 | €1,500 | 23 years | | Ventilation system | €20,000 | €800 | 25 years |
Without subsidies, the measures pay for themselves in 18 to 25 years. With KfW funding of approx. 20 %, the payback period drops to 14 to 20 years. In addition, there is the value enhancement of the property through the improved energy standard – this effect has become significantly stronger in recent years.
ESG and the consequences for financing
Lenders and banks are increasingly scrutinising energy efficiency in financing decisions. Properties with poor energy ratings are subject to risk premiums or are no longer financed at all. For owners who want to sell or refinance, energy retrofitting is therefore not only ecologically sensible but also economically vital.
Conclusion
Energy retrofitting is one of the central tasks for property owners in this decade. Those who act early benefit from subsidies, value enhancement and a future-proof property. Those who wait risk value loss and declining rentability. The most important recommendations:
- Check the energy performance certificate and have the energy condition assessed.
- Create a retrofit roadmap – not everything at once, but in sensible steps.
- Apply for subsidies in advance – always before starting the work.
- Replace the heating system first, then insulation, then windows.
- Involve experts – an energy consultant or architect helps to prioritise the right measures.
