A low-cost timber cladding system for the sustainable retrofit of masonry buildings: mechanical characterization under diagonal compression

Canada faces a severe housing crisis, coupled with an aging and underutilized building stock. This issue is exacerbated in Eastern provinces like Québec and Ontario, where old unreinforced masonry (URM) buildings are prevalent and vulnerable to natural hazards such as earthquakes, floods, and soil settlements, therefore making their rehabilitation and repurpose projects particularly challenging. To address these issues and facilitate code-compliant building reuse and conversion into housing, this study presents a low-cost and sustainable timber retrofit cladding system for improving the structural response of URM buildings typical of Eastern Canada. The proposed design, devised to accommodate an energy layer as well to improve thermal performance, is tailored to the region’s cold climate, low-to-moderate seismicity, and flood/soil settlement patterns, utilizing locally available construction practices and materials. In this paper, which focuses on quantifying mechanical performance alone, full-scale experimental testing of URM walls retrofitted with the proposed timber retrofit solution was conducted under in-plane diagonal compression. The results demonstrate that our novel design effectively delays brittle diagonal shear failures and transitions to more desirable mixed shear sliding mechanisms, significantly enhancing displacement capacity and post-cracking loadbearing performance to achieve ASCE 41–23 life safety (LS) thresholds. In addition to preliminary experimental and numerical data showing the potential for increasing URM thermal performance by over five times using biogenic insulation, the adopted retrofit solution enhances the maximum ultimate displacement of as-built walls under diagonal compression by 68 times on average, and recover 75.9 % of their loadbearing capacity on average after the first relevant was observed. Numerical simulations of tested walls is also conducted based on the Distinct Element Method (DEM), showing satisfactory agreement with experimental studies. Findings support the potential for broader application of our retrofit in the rehabilitation of Canada’s existing URM buildings, offering a practical solution to increase housing supply while minimizing environmental impact. • A low-cost modular timber structural-energy retrofit is proposed for URM buildings. • In-plane diagonal compression tests are conducted for (un)retrofitted URM walls. • The proposed cladding retrofit system alters the failure mode from brittle to ductile. • Retrofitted walls retain a substantial loadbearing capacity after initial cracking. • This research addresses housing crisis and code-compliant building reuse in Canada.