Evaluating moisture safety strategies in CLT buildings – predictions vs actual outcomes

This study evaluated moisture safety strategies and construction practices in two non-residential CLT buildings through predictive analyses and on-site observations. The measured moisture content (MC) ranged from 9%–18% in the first building (excluding the areas with damaged end-grain protection), 12%–18% in the first-floor panels of the second building (with end-grain protection), and up to 40% in its unprotected second-floor panels. Localised damage to end-grain protection and a poorly designed floor panel connection joint caused moisture issues in the first building where material replacement was necessary. In the second building elevated MC in the second-floor panels warranted mechanically aided moisture dry-out. Readiness to mitigate moisture problems was deemed necessary regardless of the protection method used against water ingress. Prolonged exposure to outdoor air, even when under temporary weather protection increased MC in the case of the first building, however the temporary weather protection proved effective in protecting against rain. Undamaged end-grain protection was also deemed effective. The predictive analyses of moisture safety strategies indicated that in 6 of 10 cases for the first building and in all cases for the first-floor panels of the second building a moisture safe outcome was expected. However, no moisture-safe outcomes were indicated for the second-floor panels of the second building. The results demonstrate the benefits of predictive analyses which likely could have prevented the selection of a solution without end-grain protection in the second-floor panels in the second building, as evidenced by measurable data. The outcomes rely on design and planning quality, so including specific moisture safety drawings and a moisture safety strategy analysis within the building design is recommended. • Prediction method aligned with the outcomes and has potential for use in practice. • End-grain protection and a protective tent provide effective moisture safety for CLT. • Prolonged air exposure, even under a protective tent, can increase MC in CLT. • Moisture monitoring and mitigation readiness are important regardless of protection. • Moisture safety relies on clear design and risk analysis; contractor expertise follows.