Improving the passive survivability of residential buildings during extreme heat events in the Pacific Northwest

Extreme heat events are becoming more frequent and more severe in the Pacific Northwest and in comparable dry-summer climates worldwide, increasing the occurrence of heat-related illness and death. Much of this risk is attributed to overheating in multifamily dwellings, particularly in neighborhoods with abundant asphalt, few trees, and limited financial resources. Air-conditioning expansion is problematic, however, because it creates vulnerability to operational costs and power outages, while expelled hot air intensifies urban heat island effects. In contrast, passive cooling strategies that deflect solar radiation and recruit the cool night air typical of Mediterranean, semi-arid, and arid climates are quite promising, but their abilities to improve residential survivability during extreme heat have not yet been explored. To understand this potential, here we investigate the extent to which well-controlled shading and natural ventilation, in some cases with fan assistance, could have diminished the hours in which indoor heat index levels exceeded 'caution', 'extreme caution', 'danger', and 'extreme danger' thresholds during the June 2021 heat wave in the Pacific Northwest; building thermal performance was simulated in EnergyPlus under conditions experienced by Vancouver BC, Seattle WA, Spokane WA, Portland OR, and Eugene OR. Strikingly, we find that in Portland, where the highest temperatures occurred, integrated shading and natural ventilation eliminated all hours above the danger threshold during the 3-day event, lowering peak indoor air temperatures by approximately 14 degrees C (25 degrees F); without cooling, all 72h exceeded this threshold. During the encompassing 10-day period, these passive measures provided 130-150h of thermal relief; baseline conditions without cooling provided none. Additionally, passive cooling reduced active cooling loads by up to 80%. Together, these results show the immediate, substantial value of requiring effective operable shading and secure operable windows in apartments in mild dry-summer climates with rising heatwave intensity, as well as public health messaging to support the productive operation of these elements.