Environmental response of a CLT floor panel: Lessons for moisture management and monitoring of mass timber buildings

Monitoring Moisture Performance of Cross-Laminated Timber Building Elements during Construction

“…At the material/sub-assembly scale, the outer layers (particularly the upper layers of horizontal elements) and the end grain at the panel edges [11,12,15,39] were identified as the most vulnerable to water ingress. Such concern was informed in part by laboratory results that suggested moisture tended to accumulate at the gaps and the interface of the upper two plies of CLT floors after wetting [11] and indications that sealants can at times negatively impact drying [39].…”

“…Comprehensive research has been done on mold and decay growth [7][8][9] in different exposure conditions to support performance-based service life design. Few studies, however, have explored the implications of moisture exposure of mass timber during construction or for accidental wetting in service e.g., [10,11]. Checking, interfacial shearing/delamination, and warpage-all observed on CLT exposed to environmental simulations within a laboratory [10][11][12] and in computer simulations [13]-are examples of moisture-induced damage that can occur as a result of heavy environmental fluctuations, particularly when involving direct exposure to liquid water.…”

“…Few studies, however, have explored the implications of moisture exposure of mass timber during construction or for accidental wetting in service e.g., [10,11]. Checking, interfacial shearing/delamination, and warpage-all observed on CLT exposed to environmental simulations within a laboratory [10][11][12] and in computer simulations [13]-are examples of moisture-induced damage that can occur as a result of heavy environmental fluctuations, particularly when involving direct exposure to liquid water. Moisture induced discontinuities, which can form already during construction, can affect various physical and mechanical properties.…”

“…Moisture induced discontinuities, which can form already during construction, can affect various physical and mechanical properties. For instance, according to Gülzow et al [10] checking of CLT lamellas can cause a reduction of the modulus of elasticity (MoE) perpendicular to the grain; Schmidt et al [11] observed a modulus of rupture (MoR) reduction of short-span CLT panels due to the effects of checks on rolling shear. Moisture-induced discontinuities occur at any depth within a panel [14] but they are typically most pronounced at the edges and connections where risk of moisture fluctuation and accumulation are the greatest [15].…”

“…These studies are also paralleled by a growing body of environmental laboratory simulations and modeling efforts, aiming at assessing the wetting-and drying-performance of CLT in various exposure, sealant, and assembly schemes [11,12,33,[35][36][37][38][39]. Research focusing specifically on overhead wetting of larger CLT specimens [11,12,33,37,39] have varying conditions, results, and insights, but generally have one common observation: CLT, even when heavily wetted, is capable of drying to acceptable MCs (e.g., <16%) in less than a half year (and in many cases less), except where certain moisture trapping conditions prevail (e.g., addition of floor/wall assembly layers such as impermeable/semi-permeable membranes and a concrete screed, wood-on-wood connections, etc.). Data from the SHM study at Brock Commons-which began construction summer of 2016-showed that after one year the vast majority of floors-which were topped with a concrete screed-were in-between 16%-20% MC (averaging about 16%), and after the second year the majority of these had dried to below 16% (averaging about 13%) [32].…”