Serial refurbishment for buildings in timber construction

Refurbishment of single- and two-familiy houses in timber construction in Austria has a large CO2-saving potential. To meet the special requirements for the refurbishment of timber constructions, a concept for the renovation to passive house respectively plus-energy house standard with special focus on ecologic construction materials was developed in this project.

Short Description




Starting point/Motivation

Former research projects have dealt with thermal ecological retrofitting of buildings made of concrete materials. This project in contrast focuses on the development of solutions for the retrofitting of light weight constructions, considering ecological building materials, passive house and plus energy technologies, a general acceptance and a serial/industrial as well as an ecological implementation. The retrofitting of light weight constructions was chosen because of the comprehensive problems on buildings physical and technical points of view. The concepts should include high prefabricated elements with integrated HVAC to guarantee a serial implementation and a nationwide dissimilation.

Until 1995 approximately 60.000 to 70.000 one and two family houses in timber construction were built. Since the standards regarding energy consumption are stricter today, these houses are up for renovation, leading to a reduced CO2 emission of 125.000 tons per year.

Contents and Objectives

Within the research project, a renovation concept using serially fabricated construction members comprising materials with small amounts of grey energy will be used. The energy standard of those houses will be improved to passive house an even plus energy house standard. Additionally, the houses should be fully habitable during the renovation. This will be achieved using a “house over house” concept, i.e. the renovation hull will be built around the existing house. Due to this construction the necessary additional house automation can be installed between the wall and the renovation hull. It is intended to establish a financing concept which finances the renovation with the money saved due to reduced energy consumption. This will minimise the effort for the owner and therefore increase the willingness to improve the energy standard of one’s home.

Due the complexity and the amount of different layers the retrofitting of light weight constructions poses a great challenge. Contrary to historical mineral constructions thermal insulation composite systems based on EPS cannot be used. On the other hand the developed concept can be used for every building construction.

The objective of the research project was the development of a retrofitting concept based on prefabricated timber elements for the upgrading of historical light weight constructions. In addition most of the buildings which were built until 1995 are one or two family houses. Many of these small buildings have extensions that restrict the use of prefabricated elements. However serial solutions are important to increase the use of prefabricated elements for retrofitting.

Another important objective is he achievement of passive house and plus energy standard. Therefore details with integrated HVAC-components are essential. The developed concept should include detail solutions, concepts for production and for assembling.


The enquiry of the historical constructions with the used building materials, of the basic structure and the thermal behavior of historical light weight constructions are the main parts of the first work package. This includes analyses of the air tightness of the building envelope and of potential thermal bridges, the calculations of the energy certificates as a basis for the evaluation of the construction and the required retrofitting.

Based on this enquiry the concepts were developed by means of two representative building typologies. In this connection the general verification and the structurally engineered realization of a serial prefabrication with integrated HVAC components pose the main parts. Besides the building physical requirements such as protection against moisture (water vapour diffusion and convection), heat protection (thermal bridges) and sound insulation, the mounting and fixing of the elements were fundamental topics. Connections of windows, balconies, projecting roofs, awnings and so on were general parts of the developed construction catalogue. The cost-effectiveness was calculated parallel to the technical developments.

With support of the project partners the developed details were transferred in an industrial production concept that includes production, assembly and also logistics. The concept should also provide the unrestricted use of the building during the retrofitting.

The developed details and the concepts for production and assembly were discussed within a workshop with representatives of the Austrian Industry of prefabricated houses. In addition the details were coordinated with colleagues from AEE intec.

A financing model was developed in a further work package.


A serial concept for retrofitting of light weight constructions was developed based on two typical building types. The concept deals with prefabricated timber elements with integrated HVAC components. The simulations prove that the attainment of passive and plus energy standard is feasable provided that it is possible to insulate the basement.

Prospects / Suggestions for future research

The realization and proving of the developed concept in the form of an actual building project is aimed for. Therefore, first conversations with builders and contractors and owners were conducted.

Project Partners

Project management

Holzforschung Austria - Research institute and accredited testing centre

Project collaborator

DI Dr. Martin Teibinger, Ing. Rupert Wolffhardt, DI Sylvia Polleres, DI (FH) Stefan Nagl
Holzforschung Austria

Project or cooperation partner

Contact Address

Holzforschung Austria - Research institute and accredited testing centre
Dipl. Forstwirt Peter Linsenmann
Franz Grill-Strasse 7, A-1030 Wien
Tel.: +43 (1) 798 26 23 - 51
Fax: +43 (1) 798 26 23 - 50