When wood-based thermal mass performs as well as concrete

• Coupling of internal thermal mass with buoyancy ventilation, experimental validation • Wood and concrete thermal mass designs compared, both achieve optimal and equivalent performance • Both test buildings reach the same targets for temperature damping (0.7) and ventilation rate (20 L/s) • Surface area of wood thermal mass increased by × 1.42 to compensate for inferior thermal properties • Temperature damping drives reliable airflow in night updraft (28.1 ± 0.4 L/s) and day downdraft (16 ± 0.4 L/s) Right-sizing thermal mass in buildings is increasingly crucial for achieving climate resilience while curtailing both operational and embodied greenhouse gas emissions. In this study, we conducted a full-scale experiment to validate a theoretical approach to optimize the distribution of internal thermal mass in concert with natural buoyancy ventilation. Ventilation is driven by the indoor temperature damping (produced by the thermal mass), with upward flow at night and downward flow during the day. Two test buildings were constructed in Alabama, USA (ASHRAE climate zone 3A), to compare the performance of wood and concrete thermal mass in this temperature-ventilation cycle. The wood and concrete thermal masses achieved temperature damping of M = 0.74 ± 0.07 and M = 0.70 ± 0.07 , respectively, where the uncertainties represent the standard deviations of the daily averages. They also produce average ventilation rates of Q = 23.2 ± 0.4 L/s and Q = 21.7 ± 0.4 L/s, where the uncertainties are the standard deviations of the measurement errors. The results suggest that bio-based materials can perform as well as concrete thermal mass by optimizing their thickness and surface area to compensate for their inferior thermal mass properties. The results also suggest that the baseline temperature damping and ventilation rate of any naturally ventilated internal thermal mass can be accurately predicted using simplified ratios that scale with the number of occupants. These ratios are useful for early design or retrofit projects when primary materials are evaluated and selected, with the goal of improving thermal resilience while limiting lifecycle carbon emissions.