Babler, Hanke, Gaál: ‘Serial renovation for large-volume buildings – high quality, fast and affordable’ Large-scale research project demonstrates an exemplary renovation system in Vienna's 3rd district
A pilot project for energy-efficient renovation is currently being implemented at Arenberggasse 4 in Vienna's Landstraße district. In November, prefabricated façade modules with integrated component activation for heating and cooling the façade will be installed on the Sozialbau AG residential building. Due to the high degree of prefabrication, the installation work will only take a few days. Serial renovation is considered a forward-looking renovation method due to its significantly accelerated implementation time and sustainable energy cost savings, and is therefore attracting a great deal of attention from experts and the housing industry.
On Wednesday, 12 November, Vice-Chancellor and Housing Minister Andreas Babler, Innovation Minister Peter Hanke and Vienna's Deputy Mayor and Housing Councillor Kathrin Gaál got a first-hand look at the renovation project.
Innovation Minister Peter Hanke: "The building sector in Austria is not only one of the major sources of CO2 emissions, but also an enormous economic factor. Research and development are important drivers for the energy transition and the decarbonisation of space heating. Every technical milestone – from passive houses to climate-neutral neighbourhoods that are to be supplied with 100% renewable energy – was preceded by research and development. The RENVELOPE research project is an excellent example of how innovative solutions can quickly bring an inhabited building out of the fossil fuel age. This creates a win-win situation for everyone: the environment, the economy and the tenants.“
Vice-Chancellor and Housing Minister Andreas Babler: "Renovating existing buildings enables an immediate reduction in energy costs for residents. This contributes significantly to ensuring that housing remains affordable in the future. Not only has there been far too much speculation in the property market over the last decade, but residents have also been exposed to the vagaries of the energy markets for far too long when it comes to heating costs. If energy consumption can be reduced by 80%, as is the case here at Arenberggasse, and the supply of locally generated renewable energy can be ensured, this automatically leads to less dependence on the energy markets and greater financial security for residents. As Austria is already largely built up, the renovation of existing buildings plays a key role here. 'Serial renovation', in which façade elements are pre-produced industrially on a large scale, can quickly make a decisive contribution here."
What is behind the new method for renovating large-volume existing buildings?
The large-scale research project RENVELOPE was launched in 2023 as part of the Climate and Energy Fund's ‘Energy Model Region (Green Energy Lab)’ programme and is now entering the home stretch. The aim of the flagship project, led by the Styrian research institution AEE – Institute for Sustainable Technologies (AEE INTEC), was to develop prefabricated modular curtain walls that, in addition to structural elements (supporting structure, thermal insulation, windows, etc.), but also building services elements (photovoltaics, heat pumps, ventilation systems, heating and cooling distribution systems, shading, risers, etc.).
In order to be able to respond flexibly to the specific requirements and furnishing preferences of each building, the project team (seventeen project partners from the fields of research, real estate, architecture, construction, building technology, timber construction and automation) developed a modular system consisting of various elements.
The individual modules are prefabricated at the factory and assembled on site, like a large jigsaw puzzle, using a crane to form a complete façade. The big advantage of this new method is that a complete thermal and energy renovation of a large-volume building can be completed in a few days with minimal disruption, while the building remains fully occupied, and without dirt or noise. In the current, final phase of the RENVELOPE project, this renovation method is being tested on three large-volume existing buildings. Following the successful application of the modular system in the renovation of the Knittelfeld vocational school in Styria, it is now the turn of the multi-storey residential building in Arenberggasse, before the first implementation series is completed with a third existing building, a student residence in Graz. In order to learn as much as possible for the further roll-out of the system, the RENVELOPE project team is monitoring all three demo buildings over a winter and summer period.
Deputy Mayor and City Councillor for Housing Kathrin Gaál: "Highest quality of living, affordable rents and leading innovation – the Viennese housing model is known far beyond Austria's borders as a role model. With 220,000 municipal flats and an additional 200,000 subsidised flats, the city provides housing for around two-thirds of Vienna's residents. These are enormous figures, which are constantly growing thanks to ongoing new construction programmes. However, we must not forget the future quality of life in existing buildings. Sustainable renovation and a renewable energy supply are the issues of the future for the living comfort of coming generations. Thanks to strong state funding, Vienna can make innovative projects such as the “serial renovation” in Arenberggasse a reality, thereby supporting the entire housing and construction sector."
The specific renovation measures in the existing residential building on Arenberggasse
The building, with its 24 rental apartments, belongs to the real estate portfolio of Wiener Sozialbau AG. It was built in 1977 as a six-storey residential building and corresponds in terms of architecture, typology and construction to a large part of Austria's stock of multi-storey residential buildings. The building's heating requirements were rated ‘C’ in the energy efficiency class, and heat was supplied via decentralised gas boilers in the 24 flats.
As part of the ongoing renovation of the building envelope and building services, a total of 60 prefabricated curtain wall modules are being installed. These modules were prefabricated in recent weeks at the factory of the contracted wood processing company and equipped with 16 cm of thermal insulation plus approx. 6 cm of compensating insulation. Riser pipes for the building services have been integrated into the modules, and a heat dissipation system for heating and moderate cooling has been prefabricated and will be automatically pressed against the existing wall during installation. In future, the flats in Arenberggasse will be heated from the outside via the existing wall and moderately cooled from the outside in summer.
Similar to wall heating, the flat arrangement of the heat dissipation system allows for low flow temperatures and high user comfort.
The existing masonry can be used as a heat storage unit and, in conjunction with a central brine-water heat pump (7.6 kW) in the basement and two additional air-water heat pumps on the roof (2 x 12.8 kW) as a flexibility element for the priority use of electricity generated on site from a photovoltaic system (10.6 kWp). The heat source for operating the central heat pump is provided by two geothermal probes located in the building's inner courtyard. In addition to the curtain wall façade and the photovoltaic and heat pump systems, insulation measures were also carried out on the top floor ceiling and in the basement – both with integrated component activation. The entire renovation is being carried out during normal operation, without the residents having to move out.
Overall, this building renovation method is expected to reduce the heating requirements in Arenberggasse by up to 80%, which will directly result in the residents' energy costs being largely decoupled from energy market prices and thus remaining predictable and affordable in the long term. The economic benefits are also obvious, namely CO₂ savings of around 100 tonnes per year, a reduction in the outflow of added value as a result of the phase-out of fossil gas, a boost to regional craft trades and sustainable value preservation of the building stock.
Bernd Vogl, Managing Director of the Climate and Energy Fund: "Our funding programmes create the best conditions for innovations to emerge quickly. We see time and again that when innovation funding is directly linked to investment funding, projects can be implemented much more quickly. Especially in the middle stages of technology maturity, where ideas are brought from the laboratory to marketable solutions, this combination helps to mitigate risks. Projects such as RENVELOPE show that Austria can use this unique strategy to create showcase projects with great potential for multiplication and scaling.”
Daniela Huber, Deputy Head of Department and Project Manager for Energy & Innovation, Project Manager at Sozialbau AG: "The main advantage of the “serial renovation” method is the speed with which the entire project can be implemented. The planning phase takes a little longer due to the level of detail involved, but the on-site implementation is completed in just eight days and is minimally invasive. This means no relocation of residents, less noise, less dust and virtually no waste on the construction site. Compared to conventional façade renovation with a composite thermal insulation system, the costs are currently still higher than for conventional renovation. However, these additional costs are clearly proportional to the additional qualities: the integration of building technology, the possibility of summer cooling, significantly reduced energy consumption and longer renovation cycles create measurable added value – ecologically, economically and socially. We see serial renovation as a forward-looking tool for accelerating renovations in large-volume residential construction, increasing comfort and energy efficiency, and thus making an important contribution to achieving climate targets."
What happens next?
Following the successful implementation of the demonstrator in Vienna, the third demonstration project is already underway, namely the ‘Serial renovation of a student residence’ in Grüne Gasse in Graz. This demonstrates how versatile and flexible the modular technologies and processes developed in the RENVELOPE project are – from social housing and educational institutions to student residences.
The aim is to use the technical and organisational knowledge gained from all three demonstrators to achieve the next stage on the way to broad market entry and to scale the method widely. Together with property developers, industry partners and the public sector, the foundations are to be laid for establishing ‘serial renovation’ as the standard solution for existing buildings in Austria.
It is particularly positive that, in the wake of the RENVELOPE research project, a number of ‘serial renovations of existing buildings’ have already been implemented (e.g. HTL Steyr) and that the project consortium is aware of around ten planned implementations and is also involved in some of them.
Christoph Brunner, Managing Director of AEE INTEC: "The principle of “serial renovation of existing buildings” is particularly suitable for large-volume buildings with simply structured façade surfaces. A study conducted as part of the RENVELOPE project on the potential of “serial renovation of existing buildings” concluded that around 70,000 buildings in Austria alone would be suitable for this method. In order to quickly tap into this potential and also the export sector, several adjustments still need to be made. In particular, it would be important for industry, politics and research to join forces in order to define concrete objectives and measures for a comprehensive roll-out. Necessary measures currently include, for example, increasing the degree of automation in module production, standardisation and complete digitalisation of the entire process (digital twin), funding incentives and appropriate accompanying measures.“