Moisture safety in CLT construction without weather protection – Case studies, literature review and interviews

RISE Research Institutes of Sweden, Division Build Environment, Building Technology, Sweden

^* Corresponding author: lars.olsson@ri.se

Abstract

This project aims to expand understanding of how cross-laminated timber (CLT) constructions, including joints, connections and attachment points, are impacted by precipitation during construction. The project’s case studies have been based on measurements of moisture contents and material sampling as well as microbiological analysis during the construction stage of the structure. The study does not include control of remediation. A literature review and interviews with seven individuals also were conducted. The results are based on two case studies with a total of four buildings. The field measurements show microbiological growth in all buildings and essentially on all investigated floor structures. Of a total of 200 analysed measuring points, half had some growth and about a third had moderate or extensive growth. Based on the outcome, it seems difficult or impossible to avoid the appearance of microbial growth during construction with CLT without weather protection. The literature review shows that microbiological analysis of CLT is extremely rare in both laboratory and field studies, which indicates that there are obvious shortcomings in the scientific work in practical studies. However, there seems to be good awareness in the literature that theoretical studies often conduct mould growth risk evaluations. In the survey, half of those interviewed believed that remediation was needed only in the case of growth visible to the naked eye. There appear to be no moisture safety assembly methods or solutions for CLT construction without weather protection or declaration of the critical moisture conditions for CLT products. As a result, it is recommended that weather protection is used, preferably complete weather protection.