The largest source of energy consumption and greenhouse gas emissions in Canada and around the world is buildings. As a consequence, building designers are encouraged to adopt designs that reduce operational energy, through both increasingly stringent energy codes and voluntary green building programs that go beyond code requirements. Among structural building materials, wood has by far the lowest heat conductivity. As a result it is typically easier to meet certain insulation targets (e.g., thermal transmission and effective thermal resistance) with wood-based wall systems when following current construction practices. Good envelopes greatly contribute to energy efficient buildings. However, there are many factors in addition to building envelope insulation levels that affect the operational energy of a building. This study aims to provide designers with information which will assist them to choose energy efficient exterior wall systems by providing energy consumption estimates for an archetypal 6-storey residential building. Comparisons were made among several exterior wall systems including light wood-framing, cross-laminated timber (CLT), steel-stud framing, and window walls, for a range of structural systems including structural steel, light wood-frame, CLT, heavy timber, and concrete. The opaque exterior wall assemblies targeted meeting the minimum thermal requirements based on the National Energy Code of Canada for Buildings (NECB. NRC 2011). A 3-D method was used to calculate effective R-values of these exterior walls by taking into account all thermal bridging, in comparison with a parallel-path flow method in compliance with the NECB. Three glazing ratios, including 30%, 50%, and 70%, and two efficiency levels for Heating, Ventilation, & Air Conditioning (HVAC) systems, termed basic HVAC and advanced HVAC, were also assessed. Whole-building energy consumption was simulated using EnergyPlus. Four climates, from Zone 4 to Zone 7, with cities of Vancouver, Toronto, Ottawa, and Edmonton to represent each climate, were selected in this study. The energy assessment was conducted by Morrison Hershfield.
Mass timber structures have the potential to change wooden construction on a global scale. Numerous mass timber high-rise buildings are in planning, under development or already built and their performance will alter how architects and engineers view wood as a material. To date, the discussion of material durability and biodegradation in these structures has been limited. While all materials can be degraded by wetting, the potential for biodegradation of wood in a mass timber building requires special consideration. Identifying and eliminating the conditions that might lead to this degradation will be critical for ensuring proper performance of wood in these structures. This article reviews and contrasts potential sources of biodegradation that exist for traditional wood construction with those in mass timber construction and identifies methods for limiting the degradation risk. Finally, future research needs are outlined.
Effective preservative treatments for Canadian glulam products are needed to maintain markets for mass timber on building facades, access markets with significant termite hazards, and expand markets for wood bridges. For all three applications, borate-treatment of lamina before gluing would be preferred as it would lead to maximum preservative penetration. However, the need to plane after treatment and prior to gluing removes the best-treated part of the wood, and creates a disposal issue for treated planer shavings. The present research evaluates the block shear resistance of glulam prepared from untreated and borate-treated lamina with a polyurethane adhesive. Borate treatment was associated with a small but statistically significant loss in median shear strength when evaluated dry; however, there was no difference between the performance of untreated and borate-treated samples when exposed to the vacuum-pressure soak/dry or the boil-dry-freeze/dry procedures. Further work is needed to modify the composition or application of the resin to improve shear strength for glulam applications and ensure consistent performance. However, overall, these data indicate that samples prepared from borate-treated lamina perform similarly in terms of block shear resistance to those prepared from untreated lamina.
Field tests of untreated and preservative-treated glulam beams in outdoor exposure, in ground contact and above ground, were inspected for decay after five years. Copper azole and ACQ-D-treated material was in excellent condition, while moderate to severe decay was present in untreated non-durable material. Early stages of decay were also noted in yellow cedar glulam in the above-ground test. Using galvanized rather than stainless steel fasteners appeared to have a protective effect against decay in untreated material, supporting the hypothesis that zinc from the sacrificial coating on galvanized bolts inhibits germination of basidiospores.
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.
Glulam manufactured from laminating stock of three species pre-treated with ACQ-D or CA was exposed outdoors in an above-ground field test using a modified post and rail test design. After six years’ exposure, early to moderate decay was found in untreated test units, while those which were preservative-treated were completely sound.
Cross-laminated timber (CLT) may require preservative treatment in markets with severe termite hazards. Given the size of CLT panels, conventional pressure treatment would not be feasible. We therefore assessed the treatability of CLT panels with an alternative low moisture uptake surface-applied penetrating process for applying termiticides. Hem-fir panels were selected for the initial tests on the grounds that western hemlock and amabilis fir are relatively treatable. Nine test panels were dip treated and stored for 7, 14, or 21 day activation periods. Borate retention ranged from 1.2 to 6.5 kg/m3 and penetration ranged from 3 to 9 mm. Longer activation periods did not result in improved penetration. Greater penetration would likely be needed to meet performance-based standards.
