Foto: Frontansicht des Biohofs Achleitner

Climate neutral buildings from the period of promoterism - ways, potentials and possibilities of implementation

The focus was on the goal-oriented and economic options, in order to achieve a CO2-neutral energy supply and hermetically sealed building envelope as well as to show high energy efficiency when using. On the other hand building protection regulations and the quality in use are to be considered.

Short Description




Starting point/Motivation

While in case of new buildings energy-saving measures are thought to be implemented already in the project, planning or construction phase, thermal insulation improvement of historic buildings can occur only afterwards. This becomes economically complicated in particular by the fact that the historic facades may not be changed due to the town planning restrictions or monument protection regulations.

Hence, the emphasis has to be placed on the inside insulation, which should be additionally treated in a constructional-physical way especially in terms of warm-bridge-effects (connection of the floor cover and dividing walls to the building envelope), than on the usually purposeful outside thermal insulation or core insulation of the building envelope.

The refurbishment of the building equipment is required to achieve the goal of a climate neutral building. Especially the generation and distribution of heat is connected with high losses of existing Gründerzeit houses. Thus the abatement of CO2- emissions to a minimum requires the usage of renewable energy sources and efficient building equipment.

Contents and Objectives

The goal of the project is the identification and demonstration of available most efficient technologies for the renovation of Gründerzeit houses with different architecture to lay the foundation for the utilization of the existing huge energy and CO2 emission reduction potential in the Austrian and international building sector.

The available refurbishment strategies will be demonstrated for defined building categories and further to real objects in a systematic approach. Based on these results the most ecologic and economic efficient refurbishment strategies will be developed. In order to make the results replicable the CO2 emission reduction potential will be collected and preliminary work for a future demonstration object is done.


Available technologies to reduce the CO2 emissions of Gründerzeit houses were collected and represented by literature researches, manufacturers and expert surveys.

The main building characteristics as e.g. open or closed structure, buildings with courtyards, protected facades, etc. were defined by structuring of common building categories.

Two workshops were used to promote the project results to relevant persons of refurbishments of Gründerzeit houses in order to promote future activities and identification of interests.

The identification and analysis of a reference group is used to show the current situation, the feasibility of strategies and to determine the potential of refurbishments in this sector. Based on these results the potential for Vienna, Austria and the Danube region is extrapolated.

The feasibility of the identified strategies is demonstrated at the end of the project for demonstration objects in order to prepare preliminary work for a potential demonstration project.


Energy-oriented refurbishments were carried out in urban regions, often punctual due to protected areas. The stimulation of refurbishments was often limited due to high expenses or restrictions by the conservation of historic monuments.

The reduction of the energy demand as well as the usage of renewable energy resources were the main parameters to reach the project goals. In general, there are many technologies for refurbishment of buildings available, but many of them are limited due to several conditions. From the constructional point of view internal thermal insulation has to be used in most cases, because many buildings are located in protected areas. There are many technologies for the energy supply of Gründerzeit houses as well. The usage of renewable energy resources is often limited to the space requirements of these technologies. The average heating demand of the reference group is about 128 kWh/m2a. Building categories were defined to classify the objects according to the building characteristics. The results of the heating energy demand show only small dependences on the building categories due to homogenous building characteristics in the categories. Larger deviations between the objects are caused by punctual refurbishments with realized thermal optimization. The largest savings can be achieved by the improvement of the thermal building envelop. An equal thermal improvement of street and courtyard located facades shows only small differences in the resulting heating energy demand in the reference group.

Due to the fact that many street located facades are protected the thermal improvement of the courtyard located facades show higher savings. In most cases box-type windows are integrated in Gründerzeit houses which only can be refurbished in case the object is located in a protected area otherwise a window replacement can be considered.

As the results of single actions, a thermal improvement of the facades offers the hugest energy saving potential. Thermal insulation of external construction components according to national building standards reduces the heating demand by 38%. Therefore a internal thermal insulation is required for street located facades in 80% of the objects. In most objects the courtyard located facades are cleared, whereby external insulation can be performed.

Further thermal improvements and the usage of controlled ventilation systems with heat recovery reduce the heating demand by 77%.

A modernization of the heat generation and distribution system reduces the CO2- emissions for heat supply by 60%. In case of ecologic orientated refurbishments CO2 emission savings of about 86% can be achieved.

The feasibility of the systematic approach was demonstrated by three selected objects. The estimated costs for the refurbishments were collected in order to evaluate the ecological efficiency as well as the economic efficiency using specific investment costs for the different refurbishment strategies. The highest efficiency from ecological point of view can be achieved by ecologic orientated refurbishments. Thus this strategy achieves the highest savings of the invested capital. From an economic point of view a refurbishment according to national standards achieves the highest efficiency due to the lowest investment costs.

According to the extrapolation of the project the share of final energy consumption in Viennese Gründerzeit houses is about 50% of the space heating requirement in private households of Vienna. The Austrian share of final energy consumption in private households is estimated by 16% and in the Danube region by 7%. Thus the refurbishment of Gründerzeit houses can achieve an important contribution to reduce CO2 emissions and therefore to fulfill climate protection targets. The project goal of a climate neutral energy supply of Gründerzeit houses can’t be fulfilled entirely. According to the rate of refurbishment savings of about 86% can be achieved. The remaining emissions can be compensated by climate reduction certificates in order to provide a climate neutral heat supply in Gründerzeit houses.

Prospects / Suggestions for future research

The results show the applicability and potential of available technologies for the refurbishment of Gründerzeit houses. The main focus of current refurbishments was the usage of economic single actions. Due to the fact that the refurbishment of historical monuments is not a standard product, in most cases a detailed planning process for refurbishment actions is required. This project gives systematic replicable approaches for future refurbishment projects for Gründerzeit houses. The project gives refurbishment strategies, costs and expectable results to involved persons in an early planning stage.

An extrapolation of the results for Vienna, Austria and the Danube region show a huge energy and CO2 emission reduction potential in this area.

Further the project show that refurbishment by factor 10 are punctually feasible in Gründerzeit houses but have to be elaborated individually for each object. The project results have an important contribution to promote the rate of refurbishment of Gründerzeit houses.

Project Partners

Project management

DI Dr. Klaus Reisinger
Allplan GmbH

Project or cooperation partner

  • DI Walter Prause, DI Heinz Feix
    Zivilingenieurbüro für Bauwesen

Contact Address

Allplan GmbH
Dipl.-Ing. Dr. Klaus Reisinger
Schwindgasse 10, A-1040 Wien
Tel.: +43 (1) 5053707 - 10

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