The outdoor climate of an area has a significant impact on housing and urban fabric as a whole, and the more extreme a climate, the more necessary it becomes to respond to it. Thus the climate should be regarded as a significant modifier of the built environment; thermal discomfort within building environments is a prevalent and significant issue throughout the developed and developing countries. There is considerable disagreement in the research community concerning whether comfort standards developed in the climate of North America and Europe are appropriate for use in other countries with more extreme climatic conditions. This research focuses on designing for the conditions of thermal comfort in hot dry climate regions. The research reports field surveys in both naturally ventilated (NV) buildings and air-conditioned (AC) buildings in summer season, with reference to Ghadames in Libya. This involves objective measurements and subjective questionnaire study with a view to testing the validity of the established thermal comfort models: Fanger's PMV model and the Adaptive model. It reviews the results from the field survey within those two types of buildings in the summer seasons of 1997 and 1998, which experiences the hot-dry climate of North Africa. It shows how the residents responded to the environmental conditions, social needs, and architectural character such as building design and thermal mass. The method of study and analysis are critically described. The subjective data was collected and tabulated by using questionnaires, which have been widely used and shown to be effective, to determine people's votes through scales modified especially for this purpose. Questionnaires were collected from households of 60 buildings: 30 old NV buildings and 30 new AC buildings involving a total of 270 participants from both types of buildings. The questionnaires compare the significance of the thermal sensation, the thermal comfort, and the preference scales of each type of building. The objective survey consisted of 19 observations of empirical data (in the 9 old NV buildings, and in the 10 AC new buildings) to validate the performance of the current thermal comfort indices. The results show that the PMV model is not valid, unless modified, for predicting the thermal comfort in old buildings, in Ghadames oasis, Libya. Thus a modification is proposed. However, the results from modem air-conditioned buildings have shown that there is good agreement between Fanger's model and the actual mean vote (AMV) values reported by the occupants in these buildings. The results from the present study show also that the neutral temperatures in old and new buildings are 31.6°C and 29.4°C respectively. The adaptive model, which is developed by Auliciems (1983), is shown to be valid, without modification, for predicting the thermal comfort of sedentary occupants in such environments. The results indicate that the construction of residential dwellings using traditional methods is more conducive to the climatic conditions of hot-dry climates and suitable for the cultural requirements and life style of the occupants. Human thermal comfort was assessed using the adaptive model, to show that the climate and personal behaviour have a significant impact on human comfort perception and building design.