In hot dry regions, the building envelope receives abundant solar radiation, which contributes to heat stress and indoor thermal discomfort. To mitigate overheating inside spaces, cooling is the main basic requirement during most of the year. However, due to the harsh climatic conditions, buildings fail to provide passively the required comfort conditions. Consequently, they are fully dependent on-air conditioning systems, which are huge energy consumers. As roofs are exposed to the sun throughout the daytime, they are estimated to be the main source of heat stress. In return, they can contribute significantly to achieve optimum comfort and energy savings when efficient design strategies are used in an early design stage. To examine the potential for cooling load reduction and thermal comfort enhancement by using cooling roof techniques in residential buildings, a study was performed in the city of Biskra (southern Algeria). Accordingly, an in-field measurement campaign was carried out on test-cells during five days in summer. Three different cooling roof techniques were addressed: (a) cool reflective white paint (CR), (b) white ceramic tiles (CT) and (c) a cool-ventilated roof (C-VR). These roofing alternatives were investigated by monitoring both roof surface temperatures and indoor temperatures. Comparative analysis showed that a cool-ventilated roof is the most efficient solution, reducing the average indoor temperature by 4.95 °C. A dynamic simulation study was also performed based on TRNSYS software to determine the best roofing system alternatives in terms of thermal comfort and energy consumption, considering the hottest month of the year. Simulation tests were run on a base-case model representing the common individual residential buildings in Biskra. Results showed that a double-skin roof combined with cool-reflective paint is the most efficient roofing solution. By comparison to a conventional flat roof, meaningful improvements have been achieved, including reducing thermal discomfort hours by 45.29% and lowering cooling loads from 1121.91 kWh to 741.09 kWh.

In hot dry climates, employing passive cooling roofs systems can provide cooling needs with less amount of electrical energy. Furthermore, when focusing on living spaces in terms of indoor thermal comfort and energy performance issues, occupant’s interaction with the building should not be underestimated. Recent studies with occupant-based focus have shown that human behaviour significantly impacts energy consumption, even more than building design. Likewise, understanding occupant’s interactions within buildings plays a key role in enhancing the indoor environment performance. To examine the potential for cooling load reduction and thermal comfort enhancement by using cool roofs in residential buildings, a study was performed. Considering a sample of twelve multi-story houses located in the city of Biskra (southern Algeria), thermal comfort conditions were analysed on the basis of a post-occupancy evaluation (POE) survey and in situ recorded measurements campaign. The POE household survey indicated that out of 43 respondents, 54% perceive indoor thermal conditions as “hot” during summer period, while 79.33% of them operate HVAC device day and night. Using interviews, the study also explores social acceptability toward implementing passive roofing techniques. Results showed that cool roof and cool tiles were the best accepted systems with 100% and 90% voted strongly agree. Furthermore, the potential of thermal comfort and energy-efficiency improvements due to cool roofs was investigated through a dynamic simulation using TRNSYS software. Results indicated that air temperature was reduced by an average of 4.11°C to 3.28°C, and cooling loads have decreased to 508.60kWh/m² and 384.54kWh/m² respectively during the hottest period of summer. Therefore, user-centric satisfaction as a research method would enhance future buildings design.

The Uncontrolled urban sprawl and the unadopted building to the environment are the main causes that generate the urban heat island (UHI) phenomenon. This phenomenon contributes to the degradation of the environmental quality of the interior and exterior spaces and increases the energy demand of buildings. In hot and arid regions, the cooling needs of space during the hot season are much greater. This situation imposes the use of electrical air-conditioning equipment for longer periods, which leads to a drastic consumption of electrical energy, implicitly, rise the greenhouse gas emissions, which in turn accentuate the phenomenon of the urban heat island. In this context, one of the most effective strategies to moderate heat stress at the urban scale is the adoption of the cooling roof technique "cool roof”. In fact, solar reflectivity (SR) and high emissivity (IE) of cool materials allow them to absorb less solar energy than conventional concrete roofs, reducing the amount of heat transferred to the atmosphere. This research aims to evaluate the impact of cool roof on the mitigation of the urban heat island phenomenon and to investigate its effect on reduction of energy consumption. Experimental work was carried out in Biskra hot and arid climate.