Development and field testing of a full-scale hybrid passive envelope system (rammed earth, straw bale, and ventilated roof) for commercial buildings

This study presents a full-scale field investigation of the temperature and relative humidity responses of two experimental building envelopes in Mansoura, Egypt, during summer 2022. Six configurations combined 200 mm stabilized rammed-earth or 100 mm fired-clay brick walls with external white finishes, natural ventilation, recycled construction-material roof components, straw insulation, and extruded polystyrene insulation. Temperature and relative humidity were recorded at 1-min intervals at identified air, contact, interface, and roof-gap locations. Comparisons were based primarily on contemporaneous internal and external records within each configuration; comparisons across monitoring periods remained descriptive. Approximate readings from the plotted records showed room-air temperatures of 28–30°C in the rammed-earth configuration with roof straw insulation and 29–31°C when internal straw wall lining was also present. During roof monitoring, temperature at the underside of the straw remained approximately 28–30°C despite larger excursions at exposed roof locations. The conventional insulated unit also moderated temperature fluctuations. Thermal stability did not ensure satisfactory humidity conditions: inner wall-contact relative humidity reached approximately 87–93% in the initial closed rammed-earth configuration, and increasing internal humidity occurred in the configuration with internal straw lining. These measurements establish short-term thermal moderation but do not quantify material moisture buffering, cooling-energy savings, or long-term durability. Differences in weather, assembly composition, and sensor position, together with unmeasured radiation, wind, and airflow, constrain causal attribution. The findings support further development of integrated passive envelopes with explicit moisture management and controlled, longer-term validation.