Sustainable Conservation and Adaptive Reuse of Historic Buildings Based on Material Performance and Environmental Response

Adaptive reuse can extend the service life of historic buildings, but its sustainability depends on whether contemporary interventions improve environmental and functional performance without accelerating material deterioration or eroding heritage authenticity. This multicentre longitudinal study compared the material, environmental, energy, functional, and heritage performance of historic masonry buildings managed under three conservation strategies. Seventy-two buildings in Guangzhou, Nanjing, and Xi’an were classified as conservation-only, material-compatible passive retrofit, or adaptive reuse with reversible environmental control, with 24 buildings in each group. Indoor temperature, relative humidity, carbon dioxide, energy use, and wall moisture were monitored throughout 2025. Wall moisture, soluble salts, visible deterioration, ultrasonic pulse velocity, surface hardness, and crack width were assessed at baseline and month 12. Functional fit, occupant satisfaction, and heritage authenticity were evaluated at the end of follow-up. Mean wall moisture decreased by 0.23 ± 0.95 percentage points in the conservation-only group, 2.09 ± 0.78 in the passive-retrofit group, and 2.37 ± 0.86 in the adaptive-reuse group. After adjustment for baseline moisture, climate location, building characteristics, exposure, occupancy, and material compatibility, month-12 wall moisture remained lower in the passive-retrofit and adaptive-reuse groups than in the conservation-only group. The adjusted difference between the two intervention groups was not significant. Visible surface deterioration and maximum crack width also showed greater improvement in the intervention groups. Soluble-salt content, ultrasonic pulse velocity, and surface hardness did not differ significantly in the prespecified repeated-measure analyses. High-humidity exposure, thermal comfort, absolute energy use, and occupant satisfaction differed descriptively across groups, but these associations were attenuated after adjustment for environmental-control intensity or occupancy. Adaptive reuse produced the highest functional-fit scores, while heritage-authenticity scores were lower than in the less intensively modified groups. Material-compatible passive retrofit and adaptive reuse with reversible environmental control both supported wall drying and reduced selected signs of surface deterioration. More intensive adaptive reuse improved functional suitability but did not provide an additional moisture benefit over passive retrofit and introduced potential energy and authenticity trade-offs. Sustainable conservation should therefore prioritize compatible passive measures and use active environmental control selectively, with material, operational, and heritage outcomes monitored independently.