ReBuildStock - Portfolio management for the decarbonisation of larger housing stocks

Initial Situation and motivation

The EU aims to reduce CO2eq emissions by 55% by 2030 (EC 2024a), with the building sector playing a key role. To achieve this, the "Renovation Wave" (EC 2020) and revised Building Directive (EPBD) were introduced (EC 2024c), aiming for energy-efficient existing buildings by 2050. Austria must increase renovation rates and provide subsidies to support low-income households, reducing energy poverty. New tools are needed to efficiently renovate large building stocks and economically implement decarbonisation strategies.

Project contents and objectives

The ReBuildStock project aims to develop a portfolio management method to assist owners of large residential building stocks in developing strategies for the rapid and socially responsible decarbonisation of their portfolio. This method addresses questions regarding current energy consumption, CO_2eq emissions, priority buildings for renovation, heating supply options, and the refinancing of deep renovations through reserves, subsidies, and rent adjustments. It also helps identify cost-efficient renovation strategies and assess medium-term financial and funding requirements.

Portfolio management method

The portfolio management method supports owners of large residential building stocks in efficiently and socially responsibly decarbonising their properties. The process is divided into six steps.

• Stock analysis: Data from facility management systems and energy certificates are collected and converted into structured datasets. Detailed and simplified calculation methods are used to assess heating demand, final energy consumption, and CO_2eq emissions, depending on data availability.
• Energy balancing: Energy balances are calculated for both the current state and planned renovation measures. The integrated energy certificate calculation model checks whether the proposed measures meet legal requirements and eligibility for subsidies.
• Classification into renovation types: Given the diversity of buildings, a uniform renovation approach is impractical. Various renovation types were developed, using decision trees to categorise buildings by construction year, building type, and energy condition to recommend tailored measures, from minor adjustments to full reconstruction.
• Evaluation of renovation measures: The focus is on decarbonising heating and hot water systems and optimising the building envelope to reduce heating demand and required heating capacity. Depending on the building type, combined measures for improving the building envelope and heating systems are selected automatically.
• Automated cost estimation and subsidy options: The method estimates renovation costs and available subsidies using a cost database containing detailed information on building components (e.g. exterior walls, windows) and HVAC components (e.g. heating systems, ventilation). This enables precise financial planning and subsidy optimisation.
• Project ranking and analysis: Based on collected data, energy indicators, and planned measures, renovation roadmaps are developed. Prioritisation is based on criteria such as heating demand, energy savings, CO_2eq reduction, heating costs, and building condition. Available investment budgets and the capacity of housing companies are also considered to ensure realistic implementation. An internal beta tool was developed to provide various evaluation options to support renovation decisions.

Findings and recommendations

Systematic portfolio management is crucial for decarbonising large housing stocks in Austria by 2040/2050. The developed method initially uses a small amount of data from facility management and energy performance certificates in order to keep costs low and deliver quick results. It can be refined using optional additional data in order to develop more precise measures and refurbishment strategies.

Current energy certificates do not provide sufficient data for effective management; thus, more detailed information on building envelopes and technical systems, along with a standardised appendix to the energy certificate, is recommended. Expanded data collection is also necessary to include information on building condition, location, and renewable energy potential, such as heat pumps, photovoltaics or district heating.

In the non-profit and private housing sector, financial and legal challenges complicate thermal renovations. Therefore, longer refinancing periods and flexible rent adjustments are suggested to reduce the financial burden on tenants. Adjustments to the Tenancy Law (MRG) are needed to expand tenant obligations for accepting decarbonisation measures and facilitate contracting solutions.

For buildings that are to be refurbished and decarbonized, it is recommended that tenant ac-ceptance is assessed at an early stage to enable demand-oriented implementation. Information measures, the involvement of tenant representatives and cost transparency promote ac-ceptance. Properties with a high level of acceptance can be prioritised.

Prioritisation of measures should consider not only CO_2eq reductions but also economic feasibility, organisational capability, and legal conditions. Reliable cost estimates for building components and technical systems are essential, requiring the development of a detailed cost database for both energy-related and non-energy-related renovations. Lastly, climate targets like the 1.5-degree goal should be translated into building portfolio strategies and integrated into national renovation plans, with binding targets tailored to building types, construction ages, and heating systems.

Project management

Energy Institut Vorarlberg

Project or cooperation partners

• AEE - Institute for Sustainable Technologies
• IIBW - Institute for Real Estate, Construction and Housing Ltd.

Energy Institut Vorarlberg
Thomas Roßkopf-Nachbaur
Campus V, Stadtstraße 33
A-6850 Dornbirn
Tel.: +43 (5572) 31202-58
E-Mail: thomas.rosskopf@energieinstitut.at
Web: www.energieinstitut.at