In Thailand, traditional houses and public buildings were constructed from materials of low thermal mass. Windows and doors in such buildings are well shaded. Open windows, doors, and even gaps in the raised floor allow all interior spaces in a building to be naturally ventilated. Prior to the introduction of air-conditioning, concrete began to replace wood as walling material. New large air-conditioned buildings have glazed and closed windows so all interior spaces require air-conditioning and forced ventilation. Under the present situation, there is a tendency to believe in the merit of thermally massive walls. This paper presents results from an experimental and simulation study on comparative energy and economic performance of thermally light and massive walls that are used to enclose air-conditioned spaces. The spaces are assumed to serve three residential functions and three commercial functions. Results related to residential functions reaffirm the merits of vernacular architecture. Results related to commercial functions are mixed. However, very massive walls are not economical. (C) 2011 Elsevier B.V. All rights reserved.