This report documents the instrumentation installed for monitoring moisture, indoor air quality and differential movement performance in a six-storey building located in the City of Vancouver. The building has five storeys of wood-frame construction above a concrete podium, providing 85 rental units for residential and commercial use. It was designed and built to meet the Passive House standard and, once certified, will be the largest building in Canada that meets this rigorous energy standard. Although the design and construction focused on integrating a number of innovative measures to improve energy efficiency, much effort was also made to reduce construction costs. One example of the design measures is the use of a highly insulating exterior wall assembly that integrates rigid insulation between two rows of wall studs as interior air and vapour barriers.
This monitoring study aims to generate data on long-term performance as part of FPInnovations’ effort to assist the building sector in developing durable and energy efficient wood-based buildings, which is expected to translate into reduced energy consumption and carbon emissions from the built environment. The monitoring focuses on measuring moisture performance of the building envelope (i.e., exterior walls, roof, and sill plates); indoor environmental quality including temperature, humidity, and CO2; and vertical differential movement between exterior walls and interior walls below roof/roof decks. In total, 79 instruments were installed during the construction.
The next steps of this study will focus on collecting and analysing data from the sensors installed, and assessing performance related to the building envelope and vertical differential movement. FPInnovations will also collaborate with CanmetENERGY of Natural Resources Canada to monitor heat recovery ventilators and to assess whole-building energy efficiency and occupant comfort. This is expected to start after the mechanical systems are fully commissioned during occupancy. Results of these upcoming phases of work will be published in future reports.
A study was initiated in late 2012 to assist in designing panelized wood roofs and other wood roof assemblies as part of the work supporting the British Columbia (BC) Advisory Group on Advanced Wood Design Solutions. The test aimed primarily to assess and compare the drying performance of different roof assemblies with built-in moisture under worst-case scenarios in the coastal climate of BC. A range of roof assemblies were built using plywood, OSB, cross-laminated timber (CLT), or laminated veneer lumber (LVL) as the roof deck. Each deck specimen was wetted using hourly spray of water for 15-20 days in the laboratory. Either self-adhered impermeable membrane, or standard roofing felt plus asphalt shingles, was used to cover the wetted top surface. Closed-cell spray foam insulation was applied on the bottom surface in several roof assemblies to assess its impact on the drying performance. Subsequent drying was carried out under three ambient conditions for three groups of specimens, beginning in February or March, 2013. Limited drying forces, except natural moisture diffusion and evaporation, were created, except for one roof assembly placed under controlled temperature gradients. The drying rates of each wood deck were monitored by weighing the roof assemblies periodically, followed by calculating the changes in the average moisture content (MC) of each wood deck. In total, 111 assemblies were tested to compare the drying rates between different wood decks and between different assemblies.
The major test results included:
The MCs of the plywood, OSB, CLT, and LVL specimens, after hourly spray in the laboratory for 15 to 20 days, were all highly comparable with those of the naturally exposed reference specimens after about two months of natural exposure from January to March. This validated the use of such laboratory wetting to simulate severe wetting scenarios on construction sites.
The four types of roof deck materials in this study showed very different water absorption and wetting potentials. The CLT specimens, as a mass timber product tested in this study, showed the lowest wetting potential, closely followed by LVL. The plywood and the OSB specimens tested had the highest MCs after wetting under both conditions.
In general the higher the material’s wetting potential, the faster it would dry under conditions allowing drying.
The CLT and LVL assemblies, covered with impermeable membrane on the wetted surfaces, showed little drying during the test periods. The use of two layers of plywood as a roof deck also showed much slower drying compared with the one-layer assemblies, when covered with an impermeable membrane on the wetted surfaces.
The combination of 15-pound roofing felt and asphalt shingles showed only slightly better vapour permeance, as indicated by the slightly better drying performance of roof assemblies, compared with the impermeable membrane used in this test.
All of the roof deck materials tested had very poor drying performance when enclosed in materials with low vapour permeance, such as impermeable membranes and closed-cell spray foam.
Among the three main drying conditions used in this study, the plywood and OSB assemblies in the shed showed the lowest drying, and those in the lab showed the fastest drying, with those in the conditioning chamber providing intermediate drying rates. Such differences appeared to correlate well with the vapour pressure differences between the saturated pressures and the partial pressures of the environments. The shed was intended to simulate covered on-site conditions in this climate.
This test indicated that, when roof panels get wet, drying during construction can be improved fairly easily for relatively permeable panels or assemblies, such as one layer of plywood or OSB, one layer of plywood or OSB covered with other materials only on one side. Favourable weather conditions and mechanical methods (e.g., ventilation and space heating) can accelerate drying. However, the ambient environment may not have much effect on the drying performance of relatively impermeable products or assemblies, including massive wood members and wood enclosed in impermeable materials. The test data also indicates that drying could take a long time, typically weeks and even months depending on environmental conditions, once wood panels get severely wet. This could allow mould growth and even decay to occur under severe circumstances. This study confirms the importance of keeping wood dry in the first place, and drying wood before enclosure when wetting occurs as the second strategy, in order to minimize moisture-related risks. Guidelines are needed to recommend best practices for on-site wood protection and moisture management in wet climates, for the use of innovative engineered wood products in larger building projects in particular.