Building high energy efficiency has become a must to reduce carbon emission from the built environment and to meet needs of consumers. Industrialized construction provides an effective way to produce highly insulated and airtight building envelopes to achieve superior building performance, such as Net Zero Energy. However, it is important that as other attributes (e.g., seismic, wind, fire, vibration, etc.) are being addressed, further research is needed to develop well rounded building envelope solutions. Meanwhile, improvement may be made in automated production equipment and software to optimize and monetize these solutions.
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.
Cross-laminated timber (CLT) has become popular in Europe for the prefabricated construction of wall, roof and flooring elements. The use of CLT in North America is gaining interest in both the construction and wood industries. Several North American manufacturers are in the process of product and manufacturing assessment or have already started pilot production.
For general principles of durability by design, the Best Practice Guide for Wood-Frame Envelopes (CMHC, 1999) and the Building Enclosure Design Guide – Wood-Frame Multi-Unit Residential Buildings (HPO, 2010) should be referred to for the design and construction of CLT buildings. The use of prefabricated CLT panels does not change the basic heat, air and moisture control design criteria for an exterior wall or roof assembly. However, different from conventional stick-built wood-frame buildings, the design of CLT building enclosures requires additional attention due to the unique characteristics of the product. CLT panels are massive solid wood elements and therefore have low vapour permeability and may provide a considerable level of insulation. They have a certain level of inherent air tightness but usually require an additional air barrier. The panels may absorb a large amount of moisture when exposed to excessive wetting and the consequent drying may be slow due to the mass of wood in such panels.
This chapter focuses on best practice heat, air and moisture control strategies for wall assemblies that utilize CLT panels in North American climate zones. The overlying strategies are to place insulation in such a way that the panels are kept warm and dry, to prevent moisture from being trapped or accumulating within the panel, and to control airflow through the panels, and at the joints and interfaces between them.
It is intended that these guidelines should assist practitioners in adapting CLT construction to North American conditions and ensuring a long life for their buildings. However, these guidelines are not intended to substitute for the input of a professional building scientist. This may be required in some jurisdictions, such as Vancouver BC, and is recommended in all areas at least until such time as CLT construction becomes common practice.
FPInnovations a effectué un essai en laboratoire afin d’étudier la teneur en humidité (TH) du bois lamellé-croisé (CLT) découlant du coulage de chapes de béton, et l’efficacité avec laquelle un enduit imperméabilisant et une membrane permettent de de prévenir cette humidification.
Thermal treatments to improve the dimensional stability and durability of wood for exterior applications impart a pleasant dark brown colour but this rapidly fades to gray when exposed to weathering. A coating may solve this problem but adhesion to oil-thermal-treated wood may be an issue. The general objective of this research is to investigate the feasibility of coating oil-thermal-treated post-Mountain Pine Beetle (MPB) lodgepole pine for above-ground residential products such as siding. This is a continuation of previous research in 2006/07 on treating post-MPB lodgepole pine sapwood with oil-thermal treatment, also funded by FII. The current project focuses on surface modification and coating systems evaluation for this treated pine by laboratory tests, and initiating field tests for monitoring long-term coatings performance.
The project was carried out in collaboration with Dr. Paul Cooper of the University of Toronto, Dr. Phil Evans of the University of British Columbia, and Dr. Sam Williams of the Forest Products Laboratory of USDA. Based on the study carried out by FPInnovations–Forintek Division, Sikkens Cetol 123 and SuperNatural showed good adhesion on oil-thermal-treated pine, but the appearance of SuperNatural was preferable for the targeted applications. Hence, SuperNatural was selected for a long-term field test in Vancouver.
Based on the study undertaken by FPL, an aluminum isopropoxide sol-gel precursor was able to improve surface adhesion of the oil-thermal-treated wood for a water-borne finish, but did not improve the adhesion for solvent-borne finishes. The oil-thermal treatment did not appear to appreciably change the hardness or Young’s modulus of the wood based on the nano-indentation measurements. It was also found that the oil-thermal-treated wood could be easily treated with hydroxymethylated resorcinol (HMR), a coupling agent for coating. Its efficacy on coatings performance is being evaluated using an outdoor exposure test.
Based on the University of Toronto’s study, the oil-thermal treatment reduced the wettability of the wood to a number of solvents and had an adverse effect on coating curing and adhesion. Light sanding improved the wetting and resulted in improved adhesion. Among all the finishes evaluated, SuperNatural clear finish formed a hard coat with good adhesion.
The study by the University of British Columbia found that plasma treatment is able to remove oil from the surface of oil-thermal-treated pine, and increased its wettability as well as adhesion to coatings. Scanning electron microscopy, confocal profileometry, and Fourier transform infra-red spectroscopy also indicated that high-energy plasma treatment impacted wood structures, particularly around pits. The consequence of the plasma treatment on coatings performance is being studied with a weathering test.
Overall, the study showed that oil-thermal-treated blue-stained pine can be coated to improve weathering performance for exterior above-ground applications. It confirmed that sanding can improve the coatings performance. The effects of a coupling agent and plasma treatment on coatings performance are to be reported. Thermal modifications may provide a promising way to improve dimensional stability and also mask blue stain for post-MPB lodgepole pine. However, the potential bleeding of oil from wood with initially intense blue stain poses a major challenge for coating application and for developing residential appearance products from the post-MPB lodgepole pine using such an oil-thermal treatment. In that case, alternative thermal treatment processes, particularly using steam as the heating medium, could be considered.
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.
En Europe, les panneaux en bois lamellé-croisé (CLT) ont gagné de la popularité pour la préfabrication d’éléments de mur, de toit et de plancher. En Amérique du Nord, on s’intéresse de plus en plus à l’utilisation du CLT dans les industries de la construction et du bois. En effet, de nombreux fabricants nord-américains sont en train d’en évaluer la production et la fabrication, ou sont déjà en mode de production.
En ce qui a trait aux principes généraux de durabilité liés à la conception et à la construction des bâtiments en CLT, le Guide des règles de l’art pour les enveloppes de bâtiments à ossature bois (SCHL, 1999) ainsi que le guide Building Enclosure Design Guide – Wood-Frame Multi-Unit Residential Buildings (HPO, 2010) demeurent les outils de référence au Canada. L’utilisation de panneaux de CLT préfabriqués ne modifie pas les principes de conception de base en ce qui à trait au contrôle de la chaleur, de l’air et de l’humidité d’un assemblage de mur extérieur ou d’un toit. Cependant, la conception de l’enveloppe d’un bâtiment en CLT diffère de celle des bâtiments traditionnels à ossature de bois et requiert une attention particulière en raison des caractéristiques uniques du produit. Les panneaux de CLT sont des éléments de bois massif, ce qui, par conséquent, leur confère une faible perméabilité à la vapeur et un degré d’isolation considérablement élevé. Malgré le fait que les panneaux de CLT possèdent un certain niveau de résistance à l’air, l’utilisation d’un pare-air supplémentaire est recommandé. Enfin, les panneaux ont la capacité d’absorber une grande quantité d’humidité lorsqu’ils sont exposés à un mouillage excessif et, en raison de la masse de bois impliquée, le cycle de séchage peut en être ralenti. Le présent chapitre se concentre sur les meilleures pratiques et stratégies de contrôle de la chaleur, de l’air et de l’humidité pour les assemblages de mur utilisant des panneaux de CLT dans les conditions climatiques nordaméricaines.
Dans l’ensemble, la stratégie est de positionner l’isolant de façon à conserver les panneaux au chaud et au sec, d’éviter l’accumulation et l’emprisonnement de l’humidité dans l’assemblage, et de contrôler l’infiltration/exfiltration d’air entre les panneaux, aux joints et aux interfaces.
On s’attend à ce que les praticiens aient recours à ces directives pour adapter la construction de CLT aux conditions nord-américaines et pour s’assurer de la longévité de leurs bâtiments. Toutefois, ces directives ne sont en aucun cas un substitut à l’apport d’un professionnel en science du bâtiment, ce qui peut être requis dans certaines juridictions, dont Vancouver en C.-B., et recommandé dans tous les aspects d’ici à ce que la construction en CLT soit devenue pratique commune.
FPInnovations conducted a laboratory test to investigate the potential wetting of cross-laminated timber (CLT) from the pouring of concrete topping, and the effectiveness of a water repellent coating and membrane in preventing such wetting.
Cross-Laminated Timber (CLT) is an engineered mass timber product manufactured by laminating dimension lumber in layers with alternating orientation using structural adhesives. It is intended for use under dry service conditions and is commonly used to build floors, roofs, and walls. Because prolonged wetting of wood may cause staining, mould, excessive dimensional change (sometimes enough to fail connectors), and even result in decay and loss of strength, construction moisture is an important consideration when building with CLT. This document aims to provide technical information to help architects, engineers, and builders assess the potential for wetting of CLT during building construction and identify appropriate actions to mitigate the risk.
The objectives of the project are to develop two-way technology transfer instruments that achieve a connection with specifiers, designers, builders, homeowners and maintenance supervisors and to explore opportunities for collaborative field studies of durability performance where information gaps exist.