Achieving and maintaining indoor thermal comfort is a crucial factor for energy saving and human health, especially in heavily occupied public buildings, such as mosque buildings. The acceptable level of thermal comfort should not be achieved at the expense of damaging the environment by using preventable energy depletion. This study aims to investigate what level thermal comfort is achieved and related issues in mosque buildings in Abha city, which has a semi-arid moderate/cold mountainous climate. The research involved a computer modelling investigation by using Thermal Analysis Software (TAS). A number of comparisons of the simulation results with actual measurement data in mosque buildings, such as temperature, relative humidity, and energy demand were conducted. Main factors influencing thermal comfort and PMV were investigated for the selected mosques. In addition, thermal performance of mosques’ fabrics and envelopes in terms of solar gain and heat loss/gain by conduction and its impacts on thermal comfort and energy demands were also discussed. The outcome showed some discomfort due to heat gain in summer and heat loss in winter. The results also revealed that the main factors behind heat gain or loss were the poor quality of the investigated mosque buildings’ envelopes, including walls, roofs, floors, windows, and doors.

The required cooling energy in buildings exceeds 65% of the total energy consumed inside buildings under the extreme climatic conditions of Saudi Arabia. The proper design of buildings’ envelopes has a considerable potential in reducing such levels, especially in public buildings. The reported study evaluated the thermal performance of mosque buildings with focus on the solar gains through the envelope elements. Computer simulations were carried out using Thermal Analysis Software (TAS). In addition, the thermal and comfort votes of the worshippers in one mosque were collected. The findings revealed uncomfortable thermal conditions, especially during summer months. The required cooling energy ranged between 37% and 55% in the investigated mosques. Investigating the solar gains of the envelope elements of one mosque indicated that the roof is the largest contributor to solar gain, which highlights the potential for future research to explore new constructional alternatives with the aim of improving the roofs’ thermal performance.