Does Building Shade Serve as a Dual Thermal–Hygrometric Regulator in a Saharan Residential Courtyard? Field Evidence, the Vegetation-Without-Shading Paradox, and Design Suggestions from Laghouat, Algeria

The summer performance of Saharan residential courtyards in developer-built (“promotional”) housing remains poorly documented. This study characterises a representative courtyard in Laghouat, Algeria (Köppen BWk), enclosed by R+3 buildings, combining in situ measurement at five stations with ENVI-met simulation. All stations remained in the EXTREME physiological-stress category (PET = 51.1–52.3 °C), with a minimum relative humidity of 9.26–10.35%; the sky view factor correlated with thermal amplitude (r = 0.936) and building shading with humidity (r = 0.977) and PET (r = −0.887). A vegetation paradox emerges: the unshaded vegetated station recorded the highest thermal surplus and lowest humidity, consistent with stomatal closure under extreme aridity, whereas the same vegetation, façade-shaded, performed best. Building shading, not ground vegetation, is the primary regulator, with a 9.5 °C surface-temperature differential between the two. These findings, specific to this single, intensively characterised courtyard, translate into six ranked design suggestions, led by built shading targeting 60–70% coverage at peak hours and temporally modulated nocturnal ventilation; the resulting assessment framework—rather than its site-specific values—offers a structure transferable to Saharan collective housing more broadly.