Wetting circumstances, expected moisture content, and drying performance of CLT end-grain edges based on field measurements and laboratory analysis

Abstract

Listen

Translate article

The moisture safety of cross-laminated timber (CLT) has gained attention as a result of feedback from construction sites and efforts have been made to protect CLT panel surfaces from wetting. However, the end-grain water absorption of CLT has often been overlooked. This study presents data from six CLT buildings where systematic moisture content (MC) measurements were made from when the CLT panels were installed until the commissioning of the buildings. Field measurement results were verified in a laboratory test where moisture uptake and moisture dry-out were monitored. On-site measurements showed that the wetting of CLT end-grain edges was common. Moisture absorption was detected in the end-grain edges in all the studied buildings and often MC > 25% persisted for many months until specific heating or drying was applied. Critical MC occurred after single rain events which suggests that a fast construction process is not always enough to avoid moisture ingress. Protection foils or membranes on the CLT panel faces did not help avoid end-grain wetting in the CLT joints. Protruding details such as floor panels or rubber bands under wall panels facilitated water intrusion. Areas with the CLT end grain exposed to ambient air experienced delamination post wetting. Laboratory test results confirmed very limited moisture dry-out in a typical CLT wall to floor joint but a potential to dry-out if the end-grain edges were exposed to dry and warm air. Specific methods to block water absorption into CLT end-grain edges should be used and joint detailing is crucial.