Dr. Ir. Hugo S.L.C. Hens is an emeritus professor of the University of Leuven (KULeuven), Belgium. Until 1972, he worked as a structural engineer and site supervisor at a mid-sized architectural office. He taught building physics from 1975 to 2003, performance-based building design from 1975 to 2005 and building services from 1975 to 1977 and 1990 to 2008. He authored and co-authored 68 peer reviewed journal papers and 174 conference papers about the research done, has helped to manage hundreds of building damage cases and acted as co-ordinator of the CIB W40 working group on Heat and Mass Transfer in Buildings from 1983 to 1993. Between 1986 and 2008, he was operating agent of the Annexes 14, 24, 32 and 41 of the IEA EXCO on Energy in Buildings and Communities. He is a fellow of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE).