The objective of this study was to assess the potential effects of climate change on the moisture performance and durability of massive timber walls on the basis of results derived from hygrothermal simulations. One-dimensional simulations were run using DELPHIN 5.9.4 for 31 consecutive years of the 15 realizations of the modeled historical (1986–2016) and future (2062–2092) climates of five cities located across Canada. For all cities, water penetration in the wall assembly was assumed to be 1% wind-driven rain, and the air changes per hour in the drainage cavity was assumed to be 10. The mold growth index on the outer layer of the cross-laminated timber panel was used to compare the moisture performance for the historical and future periods. The simulation results showed that the risk of mold growth would increase in all the cities considered. However, the relative change varied from city to city. In the cities of Ottawa, Calgary and Winnipeg, the relative change in the mold growth index was higher than in the cities of Vancouver and St. John’s. For Vancouver and St. John’s, and under the assumptions used for these simulations, the risk was already higher under the historical period. This means that the mass timber walls in these two cities could not withstand a water penetration rate of 1% wind-driven rain, as used in the simulations, with a drainage cavity of 19 mm and an air changes per hour value of 10. Additional wall designs will be explored in respect to the moisture performance, and the results of these studies will be reported in a future publication. View Full-Text
Cross-laminated timber (CLT) is a type of mass timber panel used in floor, wall, and roof assemblies. An important consideration in design and construction of timber buildings is moisture durability. This study characterized the hygrothermal performance of CLT panels with laboratory measurements at multiple scales, field measurements, and modeling. The CLT panels consisted of five layers, four with spruce-pine-fir lumber and one with Douglas-fir lumber. Laboratory characterization involved measurements on small specimens that included material from only one or two layers and large specimens that included all five layers of the CLT panel. Water absorption was measured with panel specimens partially immersed in water, and a new method was developed where panels were exposed to ponded water on the top surface. This configuration gave a higher rate of water uptake than the partial immersion test. The rate of drying was much slower when the wetted surface was covered with an impermeable membrane. Measured hygrothermal properties were implemented in a one-dimensional transient hygrothermal model. Simulation of water uptake indicated that vapor diffusion had a significant contribution in parallel with liquid transport. A simple approximation for liquid transport coefficients, with identical coefficients for suction and redistribution, was adequate for simulating panel-scale wetting and drying. Finally, hygrothermal simulation of a CLT roof assembly that had been monitored in a companion field study showed agreement in most cases within the sensor uncertainty. Although the hygrothermal properties are particular to the wood species and CLT panels investigated here, the modeling approach is broadly applicable.
This report provides an overview of major changes occurred in the recent decade to design and construction of the building envelope of wood and wood-hybrid construction. It also covers some new or unique considerations required to improve building envelope performance, due to evolutions of structural systems, architectural design, energy efficiency requirements, or use of new materials. It primarily aims to help practicioners better understand wood-based building envelope systems to improve design and construction practices. The information provided should also be useful to the wood industry to better understand the demands for wood products in the market place. Gaps in research are identified and summarized at the end of this report.
The role of the building envelope research team in this project was to assess whether midrise wood-frame (LWF) and cross-laminated timber (CLT) building envelope solutions developed by the fire research team to meet the fire provisions of the National Building Code (NBC) 2010 Part 3 Fire Protection, would also meet the NBC Part 5 Environmental Separation requirements relating to the protection of the building envelope from excessive moisture and water accumulation. As well, these wood-based mid-rise envelope solutions were to be assessed for their ability to meet Part 3 Building Envelope of the National Energy Code for Buildings (NECB) 2011. Requirements relating to heat, air, moisture, and precipitation (HAMP) control by the building envelope are included in Part 5 Environmental Separation of the NBC 2010. Part 5 addresses all building types and occupancies referred to in Part 3, but unlike requirements for fire protection, this section of the code was written more recently and is generic, including requirements that are more objective-oriented rather than prescriptive requirements pegged to specific constructions systems. The investigated methodologies developed and adapted for this study took those code characteristics into account.
Glulam and laminated veneer lumber protected by a combination of treatment with borate by two processes, and a film-forming coating, were exposed outdoors in an above-ground field test using a modified post and rail test design. After eight years’ exposure, early to moderate decay was found in untreated test units, while those which were borate-treated by either method were generally sound up to six years and showed greatly reduced decay at eight years.
International Nondestructive Testing and Evaluation of Wood Symposium
In this report, wooden members of sizes typically used in bridge construction are examined using x-ray computerized tomography (CT) to determine the presence of internal decay. This report is part of an overall study in which Douglas-fir (Pseudotsuga menziesii) glue-laminated (glulam) beams and solid sawn timbers were inoculated with brown rot fungus, Fomitopsis pinicola, and exposed to aboveground conditions approximately 25 miles (40 km) north of Gulfport, Mississippi, USA. The goal of the overall study is to develop interior decay within the test specimens and then identify and characterize the decay using a variety of nondestructive testing (NDT) techniques. One NDT technique used is x-ray CT. The pixel brightness (PB) of CT scan images is proportional to the specific gravity (SG) at that location; high SG materials appear brighter whereas low SG materials appear darker. The consumption of wood by fungus decreases the wood SG; however, fungal progression takes place in areas where sufficient moisture is present. The presence of moisture increases wood SG as detected by the CT scan, which masks the effect of the fungal decay, which is a common co-occurrence with many NDT techniques. To identify incipient decay, it is necessary to examine the ring structure both within and outside of the area of moisture. Quantifying the extent of the decay requires correlating the PB to known SG values for both dry wood and wood of varying moisture content. In this report, the relationship between wood SG, moisture content, and PB was quantified.
Japanese larch (Larix kaempferi) is an important species in China. The extensive use of Japanese larch can alleviate lumber shortage in China. Various grades of Japanese larch (Larix kaempferi) laminas were chosen to study the factors that affect the bolted joint performance...