The envelope of the Main Hall, Shinawatra University has been designed to provide, protection from energy gain. According to initial estimates, the Main Hall could achieve an overall thermal transfer value (OTTV) of 10.16 W/m(2), which is four times lower than those recommended by the Thai national standard. This study aims to evaluate the actual energy performance of the Main Hall building envelope using field measurements and simulations. The air temperature, surface temperature, and relative humidity were measured at frequent intervals, both indoors and outdoors. Hourly average meteorological data for insolations were utilized in order to calculate the solar gain by light transmission. Based on the empirical data, the energy fluxes through the envelope on eight different orientations were simulated and the average value was found within 7% of the estimated OTTV. Using the same empirical data for the outdoor condition, simulations of other common types of building envelope in Thailand were carried out for comparison. The results of the analysis show that the Main Hall's lightweight and highly insulated building envelope outperforms other commonly used heavyweight envelopes in preventing building energy gain in the hot-humid climate of Thailand. Although the use of the lightweight and highly insulated envelope helps reduce the operating and investment costs of the air conditioning system as well as the cost of building structure, it also increases the investment cost of the envelope substantially. However, the life cycle cost analysis (LCCA) reveals that the life cycle cost (LCC) of the Main Hall envelope is the most economical, and the increased investment cost of the Main Hall envelope requires a discounted payback period of only 3-5 years, depending on the envelope types used in the comparison. Furthermore, it should be noted that greater savings and a more favorable pay back period could be obtained if this highly energy efficient envelope is applied to other typical buildings, especially high-rise structures in urban areas. (C) 2008 Elsevier B.V. All rights reserved.