This literature review aims to provide a general picture of retrofit needs, markets, and commonly used strategies and measures to reduce building energy consumption, and is primarily focused on energy retrofit of the building envelope. Improving airtightness and thermal performance are the two key aspects for improving energy performance of the building envelope and subsequently reducing the energy required for space heating or cooling. This report focuses on the retrofit of single family houses and wood-frame buildings and covers potential use of wood-based systems in retrofitting the building envelope of concrete and steel buildings.
Air sealing is typically the first step and also one of the most cost-effective measures to improving energy performance of the building envelope. Airtightness can be achieved through sealing gaps in the existing air barrier, such as polyethylene or drywall, depending on the air barrier approach; or often more effectively, through installing a new air barrier, such as an airtight exterior sheathing membrane or continuous exterior insulation during retrofit. Interface detailing is always important to achieve continuity and effectiveness of an air barrier. For an airtight building, mechanical ventilation is needed to ensure good indoor air quality and heat recovery ventilators are typically required for an energy efficient building.
Improving thermal resistance of the building envelope is the other key strategy to improve building energy efficiency during retrofit. This can be achieved by: 1. blowing or injecting insulation into an existing wall or a roof; 2. building extra framing, for example, by creating double-stud exterior walls to accommodate more thermal insulation; or, 3. by installing continuous insulation, typically on the exterior. Adding exterior insulation is a major solution to improving thermal performance of the building envelope, particularly for large buildings. When highly insulated building envelope assemblies are built, more attention is required to ensure good moisture performance. An increased level of thermal insulation generally increases moisture risk due to increased vapour condensation potential but reduced drying ability. Adding exterior insulation can make exterior structural components warmer and consequently reduce vapour condensation risk in a heating climate. However, the vapour permeance of exterior insulation may also affect the drying ability and should be taken into account in design.
Overall energy retrofit remains a tremendous potential market since the majority of existing buildings were built prior to implementation of any energy requirement and have large room available for improving energy performance. However, significant barriers exist, mostly associated with retrofit cost. Improving energy performance of the building envelope typically has a long payback time depending on the building, climate, target performance, and measures taken. Use of wood-based products during energy retrofit also needs to be further identified and developed.
Transformative Technologies Program identifierSeries Energy Efficiency of Advanced Building Systems
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.
A comparison of operational energy consumption among these different exterior wall systems for this archetypal 6-storey building has shown that accounting for thermal bridging is critically important for improving thermal performance of building envelopes. Wood-based systems including light wood-frame walls, CLT, and wood-framed infill walls in concrete structures have inherently lower thermal bridging compared with other systems, such as steel-frame walls in steel and concrete structures, or window walls in concrete or timber structures. Conclusions are provided for specific climates and cities in Section 4.2. General conclusions and highlights are summarized as follows:
Building envelope influences only the energy required for space conditioning. The space heating energy consumption ranged between 28% and 49% of the entire building energy consumption, when the basic HVAC type was used, for the four cities assessed in this study. An efficient HVAC system would further reduce the proportion of space heating energy consumption. The rest of the energy is used for hot water and electrical appliances etc.
Compared to the NECB-compliant calculation, the 3-D method showed a greatly reduced effective R-value of the opaque wall assemblies due to thermal bridging. Steel-stud wall assemblies showed much larger reductions in effective R-values than wood-based wall assemblies.
Wood-based walls in a light wood-frame building, or a CLT building, would improve building energy efficiency, with total energy savings ranging from 3% to 9%, compared to a concrete building with steel-stud walls, depending on the HVAC type and the glazing ratio, when the 3-D method was used for calculating thermal resistance. The energy savings were higher in colder climates, such as Toronto, Ottawa, and Edmonton, than in Vancouver.
The use of wood-frame infill wall in concrete structure improved the whole building energy efficiency by up to 6% depending on the climate, relative to the use of steel-stud infill walls, under the same HVAC (basic or efficient type) and glazing ratio (30% or 50%).
Concrete structures typically have much higher glazing ratios than wood buildings. The wood-framed building, with exterior-insulated walls meeting the thermal insulation requirements and at a glazing ratio of 30%, showed whole-building energy savings of about 13-18%, compared to a concrete structure with window walls at a glazing ratio of 70%.
Simply adding insulation (e.g., exterior insulation) in a building envelope while ignoring thermal bridging is not the most effective way to improve building energy efficiency.
The thermal bridging at window transitions greatly reduced the effective R-values of the opaque walls and consequently the whole-building energy efficiency. The higher the glazing ratio was, the larger the impact would be. Window wall with a high glazing ratio would further reduce building energy efficiency, compared with regular windows.
The energy efficiency of the HVAC system used in a building had the largest impact on the whole-building energy efficiency, compared to the impacts caused by exterior wall systems, glazing ratios, or thermal bridging at various details.
The energy efficiency measures studied in this report delivered higher energy savings in colder climates, such as Montreal, than in warmer climates, such as Vancouver.
It is recommended that future effort be put into further developing tools for practitioners to account for thermal bridging more conveniently.
The North American product standard for performance-rated cross-laminated timber (CLT), ANSI/APA PRG 320, was published in 2012. The standard recognizes the use of all major Canadian and US softwood species groups for CLT manufacturing and provides design properties for specific CLT layups with visually graded and E-rated/MSR laminations. While design properties for CLT layups with Spruce-Pine-Fir and Douglas fir-Larch laminations are specified in the current standard, no design properties are indicated for CLT layups with Hem-Fir laminations.
Design properties for two proposed CLT grades manufactured with Hem-Fir lumber were developed. These include a CLT layup with visually graded laminations and another layup with E-rated/MSR laminations. Design properties for these two CLT layups were calculated separately for use in Canada and the US.
Supporting information for the addition of design properties for Hem-Fir grades to the CLT product standard was generated. Recommended amendments to the CLT product standard include durability and wood failure requirements of bondlines, and design properties for Hem-Fir layups.
This project evaluated a number of opportunities to coastal producers related to kiln drying issues such as drying practices related to high-value products, drying with superheated steam vacuum and internal core temperature monitoring for large timbers during the heat-up phase. In summary, this project included several laboratory studies to evaluate the using superheated steam/vacuum (SS/V) for drying 7/8”x 6, green western red cedar lumber, and 8x8 and 5x(5,6,7,8,9,10,12) Douglas-fir timbers. SS/V drying yielded faster drying schedules when compared to the results obtained in industrial conventional kilns. The results obtained from the SS/V drying of WRC indicated the potential benefits of technology for drying specialty products especially when compared to drying times obtained with conventional drying (longer than 7 days). However, the results obtained also emphasize the importance of green sorting that is, sorting prior to drying to optimize drying times and reduce the variation of final moisture content.
For large cross section Douglas-firs the drying times were between 3 and 14 days depending on the severity of the drying schedule and initial moisture content distribution. The influence of moisture content and cross section during the early and late stages of the heating process were evaluated on 5x5, 6x6 and 8x8 Douglas fir timbers. Thermodynamic equilibrium was reached after 20 hours regardless of moisture content or cross section size. The knowledge is intended to be used to design conventional drying schedules for large cross section timbers.
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.
Two of the major topics of interest to those designing taller and larger wood buildings are the susceptibility to differential movement and the likelihood of mass timber components drying slowly after they are wetted during construction. The Wood Innovation and Design Centre in Prince George, British Columbia provides a unique opportunity for non-destructive testing and monitoring to measure the ‘As Built’ performance of a relatively tall mass timber building. Field measurements also provide performance data to support regulatory and market acceptance of wood-based systems in tall and large buildings.
This report first describes instrumentation to measure the vertical movement of selected glulam columns and cross-laminated timber (CLT) walls in this building. Three locations of glulam columns and one CLT wall of the core structure were selected for measuring vertical movement along with the environmental conditions (temperature and humidity) in the immediate vicinity. The report then describes instrumentation to measure the moisture changes in the wood roof structure. Six locations in the roof were selected and instrumented for measuring moisture changes in the wood as well as the local environmental conditions.
All sensors and instrumentations, with the exception of one, were installed and became operational in the middle of March 2014, after the roof sheathing was installed. The other instrumentation was installed in July 2014. This report presents performance of the building during its first year as measured from topping out of the structure. In the end, the one-year period covers six months of construction and six months of occupancy. This is the first year of a planned five-year monitoring.
The first year’s monitoring showed that the wood inside the building had reached moisture content (MC) of about 4-6% in the heating season, from an initial MC of 13% during construction. Glulam columns were extremely dimensionally stable given the changes in MC and loading conditions. With a height of over 5 m and 6 m, respectively, the two glulam columns measured in this study showed very small amounts of vertical movement, each below 2 mm. The cumulative shortening of the six glulam columns along the height of the building would be about 8 mm, not taking into account deformation at connection details or effects of reduced loads on upper floors. The CLT wall was found to be also dimensionally stable along the height of the building. The measurements showed that the entire CLT wall, from Floor 1 to Floor 6, would shorten about 14 mm. The CLT floors, however, had considerable shrinkage in the thickness direction, and therefore should be taken into consideration in the design and construction of components, such as curtain walls, which are connected to the floors. In terms of the roof performance, two locations, both with a wet concrete layer poured above the plywood sheathing, showed wetness during construction but dried slowly afterwards. The good drying performance must be attributed to the interior ventilation function designed for the roof assemblies by integrating strapping between the sheathing and the mass timber beams below. Overall this monitoring study shows the differential movement occurring among the glulam columns and the CLT wall is small and the wood roof has good drying performance.
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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.
The current study aims at evaluating the integrity failure (i.e. passage of hot gases or flames through the assembly) of CLT assemblies connected together using four types of commonly used panel-to-panel joints when exposed to the standard CAN/ULC S101 “Standard Method of Fire Endurance Tests of Building Construction Materials”  fire resistance time-temperature curve. The four types of joints include: 1) half-lapped, 2) internal spline, 3) single surface spline and 4) double surface splines. 301009649
There is a need to evaluate TCC systems under fire conditions to understand how shear connectors will perform and might affect the fire performance and the composite action of the assembly. This project evaluates the fire performance of TCC assemblies based on their structural resistance, integrity and insulation when exposed to a standard fire, as well as how mass timber and concrete interact. This study involves full-scale fire resistance tests on composite wood-concrete floors using two types of shear connectors. 301009649