At the ‘Smart Retrofitting’ event in Darmstadt, Germany, the building owners described the entirely different kind of living comfort as ‘incredible’. Noise also remains outside. Over 40 energy consultants accepted the invitation to the ‘Passive House on Tour’ kick-off event and listened intently as the family reported on the positive changes in their energy-efficient home retrofit.
The aim of the new ‘Passive House on Tour’ series is to present highly energy-efficient projects in theory as well as in practice and to support the implementation of a high level of energy efficiency on site. Further events are in preparation.
level of living comfort
The entire family is enthusiastic about the newly gained high level of living comfort: "Previously, we couldn't have imagined such a big difference," says homeowner Kolja Hanke at the ‘Smart Retrofitting’ event (in German ‘Sanieren mit Köpfchen’). This confirms what architect Georg Zielke had already stated in the morning during the workshop: the family is amazed by the entirely different indoor climate."
"Before, we often sat on the couch with a blanket even in summer because it was simply too cool. The overall level of comfort has improved so much, it's incredible. There is now a completely different atmosphere inside the house," says Hanke, describing the different living conditions.
Warmth in winter, heat protection in summer
The detached house in Darmstadt, built in 1928, has been transformed into a comfortable home since 2023
The family from Darmstadt opened the doors of their building for the ‘Passive House on Tour’ kick-off event, allowing participants to look at the details of an energy-efficient retrofit in practice.
The detached house in Darmstadt, built in 1928, has been transformed into a comfortable home since 2023 autumn. Most of the exterior work has been completed, while work on the inside of the house is still ongoing.
energy-efficient retrofit
Passive House components have been used everywhere, from the cellar to the roof and the charm of the building remains the same. An essential part of the energy-efficient retrofit is the excellent thermal protection of the entire building, which ensures pleasantly warm rooms in winter and protects against heat in summer.
The building retrofit concept also includes the installation of a ventilation system with heat recovery and the reduction of thermal bridges.
Heating and cooling, if needed
Specifically, the foundation of the building, the exterior walls, and the roof were thermally insulated. The new windows are triple-glazed and are of Passive House quality.
The ventilation system with heat recovery ensures controlled air exchange; of course, ventilation via the windows is still possible. The ducts of the ventilation system are routed mainly along the former chimney shaft and are integrated into the interior finish.
Heat pump, split system air conditioning units
On the thermally insulated roof of the house, a PV system will soon be producing a peak electricity output
Instead of a gas boiler, there is a heat pump with a buffer storage tank for hot water in the basement. Three split system air conditioning units are installed in the house, which distributes the heated air and can also be used for cooling if required.
On the thermally insulated roof of the house, a PV system will soon be producing a peak electricity output of around 11 kilowatts for self-consumption.
Energy consumption before and after
Before the energy retrofit, the family used around 3,300 m3 of natural gas per year for heating and hot water generation using the gas boiler, an energy equivalent of around 33,000 kWh per year. In addition, around 6,000 kWh were required for household electricity. Altogether, the equivalent of around 40,000 kWh was consumed between these two energy sources.
After the energy retrofit, the combined consumption for the heat pump and domestic electricity will be around 2,500 to 3,000 kWh of externally generated electricity. This is just a fraction of the previous values. Accordingly, the utility costs will be significantly lower in the future for homeowners.
The best time
"The best time for an energy-efficient retrofit is when components are due to be replaced anyway."
"Then, components should be selected that will reliably provide a high quality to significantly reduce the energy demand. This is what was done for this detached house," explains Berthold Kaufmann of the Passive House Institute.
Putting theoryThe Passive House Institute is monitoring this retrofit as part of the EU outPHit project and organized the workshop
This idea of replacing what needs to be retrofitted anyway also applies if the retrofit is carried out in stages instead of all at once. The aim is to achieve the highly energy-efficient EnerPHitStandard, continues Kaufmann, who during the workshop presented both the general aspects of energy-efficient retrofits and the specific steps involved in the case of the detached house in Darmstadt.
The Passive House Institute is monitoring this retrofit as part of the EU outPHit project and organized the workshop. Together with other colleagues and the architect, Kaufmann discussed various insulation materials, the airtightness of the building envelope, and the installation of the ventilation system and new windows. The subject of heat pumps and the challenges of insulating stairways were also discussed in detail.
timber frame construction
Lunch was followed by the hands-on experience: the energy consultants made the (short) walk to the property. There, they were able to witness the implementation of the retrofitting steps discussed previously, including the insulation of the building with mineral wool on the north side and the timber frame construction with blown-in cellulose for the other three walls.
The building owners also described the deep retrofitting process of their home, which has been underway since autumn 2023.
Demolition or renovation?
Although the owners wanted to preserve the building from the outset, as building owner Kolja Hanke explained during the workshop, demolishing the house was also discussed:
Among other things, the architect was concerned about the almost hundred-year-old brickwork. However, this problem was solved thanks to the excellent thermal protection using Passive House components.
Energy-efficient construction projects
Significantly improved building envelope means that noise from passing aircraft no longer disturbs people's sleep
Hanke also reported that the significantly improved building envelope means that noise from passing aircraft no longer disturbs people's sleep. Although not a specialist, Hanke carried out a lot of the work himself.
When private individuals joined the tour in the afternoon, Patrick Voos, Head of the Office for Climate Protection and Climate Adaptation, explained the funding programs for highly energy-efficient construction projects that are offered by the city of Darmstadt.
‘Absolutely coherent concept’
Passive House on Tour aims to support various stakeholders such as energy consultants, local authorities, architects, and other building stakeholders in implementing a high level of energy efficiency on site.
The response to the ‘Smart Retrofitting’ workshop and thus to the first regional event of ‘Passive House on Tour’ was very positive: the fact that the Passive House Institute discusses high energy efficiency with energy consultants, and that detailed questions can be clarified and implementation is demonstrated in practice is an ‘absolutely coherent concept’, summarised one participant from Gersthofen in Bavaria, Germany.
To be continued in autumn
Further events are in preparation for autumn this year and for 2025, each with a different thematic focus and aimed at different target groups and regions.
‘Passive House on Tour’ is an additional event organized by the Passive House Institute to complement the International Passive House Conference. The 28th International Passive House Conference will take place in 2026.