1 INTRODUCTION Intervention in ancient buildings aiming to preserve the heritage is highly challenger, with regard to the difficulty to understand the existing construction and to propose an adequate retrofit, in comparison with the design of a new building over a blank sheet. However, the rehabilitation needs will increase as the built heritage ages and the economic and social conditions will favour the return to the urban cen- tres. Rehabilitation and retrofit are currently major is- sues in the construction industry, focusing the atten- tion of many researchers in an international level. The research motivations may vary among heritage preservation, economical concerns, environmental management or urban revitalization. Sustainability issues in buildings were initially concerned with thermal efficiency, due to the long use phase, that represented the greatest share of en- ergy consumption in the whole life cycle of the building. A great effort has been done in recent years to promote energy efficiency in buildings, with the increase in mandatory insulation of the outer shell, as well as the use of more efficient HVAC (Heating, Ventilation and Air Conditioning) sys- tems. It is actually possible to design "zero energy buildings", or even buildings that are featured to produce energy, therefore having a positive energy balance. To keep improving the environmental pro- file of buildings after this achievement, the focus should now be shifted to the construction phase and the energy embodied in the construction materials and processes (Rossi et al., 2012). 2 SUSTAINABILITY Sustainability may be assessed throughout three dif- ferent perspectives, which should work in combina- tion: the economical, the environmental and the so- cial impacts. 2.1 Rehabilitation Rehabilitation of ancient buildings certainly produc- es impacts in the three categories, being some of them more remarkable than the others. On the economical point of view, the rehabilita- tion of ancient buildings in city centres may be im- portant to the city's economical revitalization. On the other hand, in case the building presents an average good condition, its retrofit may be cheaper than the construction of a new one. Concerning environmental issues, rehabilitation is a means of reuse existing structures, thus extending its materials life span. Reducing the demolition needs means limiting the residues production and al- so limiting the demand for new products. On the social perspective, rehabilitation of an- cient buildings may be analysed under two major highlights: the valorisation of a region and the crea- tion of jobs due to the fact that working in ancient buildings, normally requires more man work than new building construction. 2.2 Prefabrication and Standardization Abdallah (2007) argues that the use of prefabri- cated methods provides two main benefits for the construction industry: the first of them is the lower cost of the structures, with quality improvement over Sustainable design of prefabricated solutions for the rehabilitation of ancient buildings A. C. Coelho, J. M. Branco, P. B. Lourenço ISISE, Dept. of Civil Engineering, University of Minho, Guimarães, Portugal H. Gervásio ISISE, Dept. of Civil Engineering, University of Coimbra, Coimbra, Portugal ABSTRACT: A wood-based “kit-of-parts” for the rehabilitation of existing buildings is under development. The aim is to merge the benefits of the standardized manufacture, with the flexibility needed to suit the spe- cific requirements of the built heritage. The proposed system should be reversible, flexible and adaptable, while ensuring the adequate structural, thermal and acoustic performances. Mechanical joints, reversible if possible, should be used for the connections with the existing construction. Light solutions, allowing on site adjustment and future material separation are preferable.