Nichole Wapple, M.Eng. 2014, LEED Green Assoc.
Supervisor: Dr. Rodrigo Mora
Cross-laminated timber (CLT) is a composite wood product consisting of several layers of wood boards stacked crosswise. Its use in building construction for prefabricated wall, floor, and roof structures is gaining popularity in North America. Air leakage along joints between the panel boards or along cracks and checks in the wood can create performance problems, particularly in canopies or overhangs where the structures bypass the building enclosure, or when used in interior fire-rated assemblies. This project obtained data on the air tightness of CLT panels, both with regards to sealing joints between panels and to air flow through/within the panels, to provide information that designers can consider when using CLT panels in environmental separations.
Air leakage testing was conducted based on the methodology of ASTM E283-04 “Standard Test Method for Determining Rate of Air Leakage through Exterior Windows, Curtain Wall, and Doors Under Specified Pressure Differences Across the Specimen,” at a test pressure differential of 75 Pa. Three-ply and five-ply panels constructed from eastern Canadian SPF timber were tested, without edge gluing. The test set-ups were configured to isolate the air leakage either parallel or perpendicular to the cracks.
The testing suggests that the air-tightness of joints is dependent on the workmanship and location of the joint sealant, as well as the panel configuration in the case of the surface spline joints: with good sealant application, very low air leakage rates (o.007 L/s at 75 Pa) were achieved. For testing air leakage through the panels, the presence of large joints and gaps between boards contributed significantly to localized air flow through the panel, whereas panels with tight boards achieved high air-tightness (>0.055 L/s*m at 24 Pa with large gaps vs 0.002 L/s*m with tight boards). In either case, both air leakage rates are best represented on a per-metre basis as they represent the air flow through lengths of joints and interfaces. To consider the localized air leakage contributions to the enclosure as a whole, designers should look to evaluate area-averaged leakage based on the joint or interface lengths and the results herein, divided across the total enclosure areas. However, the effects of moisture transport through the localized air leakage should not be ignored.