Towards Predicting the Drying Response of Cross-Laminated Timber (CLT) Roof Assemblies in Service - The Impact of Assembly Design and Construction on Hygrothermal Performance and Mould Risk

<p dir="ltr">Exposure to wetting is a concern during mass timber construction and service. Mass timber roof assemblies are particularly susceptible to bulk water inundation and sustained moisture loading in the form of surface ponding. Because wood is a hygroscopic material, cross-laminated timber (CLT) panels absorb and store moisture during and after exposure to bulk water. Understanding the moisture conditions and drying response of mass timber during construction and service can impact a roof assembly’s performance and occupant health due to moisture-related mould risk.</p><p dir="ltr">This research utilizes a field laboratory, a field-testing site, and simulation-based research towards predicting the drying response and mould risk of CLT in roof assemblies based on moisture control and mitigation strategies implemented during design, construction, and/or in-service. The data collected from both the purpose-built field laboratory and the field-testing site was analyzed based on dry-out rate, dry-out period, and moisture distribution through the CLT roof panels. The dry-out models developed from this data were subsequently used to calibrate a one-dimensional hygrothermal model for additional simulation-based research.</p><p dir="ltr">The hygrothermal model calibration method developed for this research was validated by both the field laboratory and field-testing data collected. Empirical mould models were implemented using the collected data and were quantitatively and qualitatively compared based on their numerical frameworks as well as the format and function of their results. Finally, the culmination of this research was the development and testing of a parametric decision-making tool: the CLT Roof Assembly Moisture and Mould (CRAMM) Risk Assessment Tool.</p><p dir="ltr">This tool provides a framework for quantifying the impact of design- and construction-based moisture control and mitigation strategies on the drying response of CLT in roof assemblies and subsequent mould risk. The results generated by this tool ultimately provide a metric by which to deterministically and/or comparatively scale the impact of moisture control and mitigation strategies. Use of the CRAMM Risk Tool was demonstrated using the data collected from the field-testing site.</p>