Emergy (spelled with an m) is the energy of one kind, usually solar energy, which is required to make a service or product. The yearly emergy con sumption/production of a building is evaluated considering the Solar Energy Laboratory (LESO) building on the campus of the Swiss Federal Institute of Technology of Lausanne (Switzerland). This experimental building was constructed according to special environmental considerations, such as important the use of passive gains (heat emitted from solar radiations, electric appliances and building users). It is therefore characterized by a very low energy consumption, equal to 232 MJ/m(2) year. The LESO building is occupied by faculty and students. Undergraduate and graduate students as well as faculty represent information inputs to the system with their emergy accounting for 94.6% of the emergy inputs to the building, equal to 3.3E18 sej/year (solar emjoules per year). "Educated students" (students who have completed a semester project, master's or PhD research in the laboratory), publications, courses and services are the main outputs of the system. The four outputs are considered as co-outputs, as such the total energy associated to the operation of the building as a structure is entirely assigned to each of them. The evaluation established that a student leaving the LESO building has a transformity (emergy per unit energy) equal to 2AE8 sej/J, which is about three times higher than the one which he/she had upon arrival, representing the knowledge gained through conferences and interactions with other students and professors. Considering only energy and materials inputs, electricity was established to be the largest input to the system (2.7E16 sej/year). The total emergy of the material inflows was determined to equal 1.7E16 sej/year, paper being the largest material input (5.7E15 sej/year). The specific emergy (per mass) of some common building materials was also evaluated and compared to NRE (non-renewable energy). Finally, the question of uncertainties related to the determination and use of average transformities and emergy per mass values is addressed, and advantages and drawbacks of the emergy method are discussed in relation to other common evaluation methodology (exergy, embodied energy, life-cycle analysis). (c) 2004 Elsevier Ltd. All rights reserved.