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.
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.
This monitoring study aims to generate field performance data from a highly energy efficient building in the west coast climate as part of FPInnovations’ efforts to assist the building sector in developing durable and energy efficient wood-based buildings. A six-storey mixed-use building, with five storeys of wood-frame residential construction on top of concrete commercial space was completed in early 2018 in the City of Vancouver. It was designed to meet the Passive House standard. The instrumentation aimed to gather field data related to the indoor environment, building envelope moisture performance, and vertical movement to address the most critical concerns among practitioners for such buildings.
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...
This monitoring study was initiated to collect performance data from a highly energy efficient, six-storey building located in the coastal climate of British Columbia. This work focuses on the following objectives by installing sensors during the construction:
· To provide information about the indoor environment of a highly energy efficient building
· To provide field data about the durability performance of an innovative high energy efficiency exterior wall solution for mid-rise wood-frame construction
· To provide information on the amounts of vertical movement in wood-frame exterior walls and interior walls below a roof/roof deck
This report summarizes basic wood-moisture relationships, and reviews conditions conducive to adverse consequences of wetting, such as staining, mold growth, decay, strength reduction, and dimensional change and distortion. It also outlines solutions and available resources related to on-site moisture management and design measures. Sorption, including desorption (i.e., loss of moisture) and adsorption (i.e., gain of moisture), is the interaction of wood with the water vapour in the ambient environment. The consequent changes in the amount of bound moisture (or “hygroscopic moisture”) of pre-dried wood affect the physical and mechanical properties. However, the core of a mass timber responds slowly and is well protected from fluctuations in the service environment. Mold growth and fungal staining may occur in a damp environment with a high relative humidity or sources of water. Sorption alone does not increase the moisture content (MC) of pre-dried wood above the fibre saturation point and does not lead to decay. Wood changes its MC more quickly when it absorbs water compared with sorption. This introduces free water (or “capillary water”) and increases the MC above the fiber saturation point. Research has shown that decay does not start below a MC of 26%, when all other conditions are favourable for fungal growth. Decay can cause significant strength reduction, for toughness and impact bending in particular. For a wood member in service, the effect of decay is very complicated and depends on factors, such as the size of a member, loading condition, fungi involved, location and intensity of the attack. Appearance of decay does not reflect true residual stiffness or strength. For wood-based composites severe wetting without decay may affect the structural properties and performance due to damage to the bonding provided by the adhesive inside.
There are large variations among wood species, products and assemblies in their tendency to trap moisture and maintain durability. For a given wood species, the longitudinal direction (vs. the transverse directions) and the sapwood (vs. heartwood) absorb water more quickly. Capillaries between unglued joints (e.g., some CLT, glulam), exposed end grains, and interconnected voids inside a product increase the likelihoods of moisture entrapment, slow drying, and consequently decay. Many mass timber products, composites in particular, may be modified to reduce these issues. Measures should also be taken in design, during construction, or building operation to reduce the moisture risk and increase the drying ability. It is also important to facilitate detection of water leaks in a mass timber building and to make it easier to repair and replace members in case damage occurs. Preservative-treated or naturally durable wood should be used for applications that are subjected to high moisture risk. Localized on-site treatment may be appropriate for specific vulnerable locations. Changing environmental conditions may cause issues, such as checking, although it does not compromise the structural integrity in most cases. Measures may be taken to allow the timbers to adjust to the service conditions slowly (e.g., through humidity control), particularly in the first year of service.
Overall there is very little information about the potential impacts that various wetting scenarios during construction and in service could realistically have on mass timber products and systems. The wetting and drying behaviour, impacts of wetting and biological attack on the structural capacity, and the behaviour under extreme environmental conditions, such as the very dry service environment that occurs during the winter in a northern continent, should be assessed to improve design of mass timber buildings.
This study aims to generate moisture performance data for several configurations of highly insulated woodframe walls meeting the RSI 3.85 (R22 eff) requirement for buildings up to six storeys in the City of Vancouver. The overarching goal is to identify and develop durable exterior wood-frame walls to assist in the design and construction of energy efficient buildings across the country. Wall panels, each measuring 1200 mm wide and 2400 mm tall, form portions of the exterior walls of a test hut located in the rear yard of the FPInnovations laboratory in Vancouver. Twelve wall panels in six types of wall assemblies are undergoing testing in this first phase. This report, first in a series on this study, documents the initial construction and instrumentation.
This new study aims to generate hygrothermal, particularly moisture-related performance data for light wood-frame walls meeting the R22 effective (RSI 3.85) requirement for buildings up to six storeys in the City of Vancouver. The overarching goal is to identify and develop durable exterior wood-frame walls to assist in the design and construction of energy efficient buildings across the country. Twelve test wall panels in six types of wall assemblies are assessed in this study. The wall panels, each measuring 4 ft. (1200 mm) wide and 8 ft. (2400 mm) tall, form portions of the exterior walls of a test hut located in the rear yard of FPInnovations’ Vancouver laboratory. This report, second in a series on this study, documents the performance of these wall assemblies based on the data collected over 19 months’ period from October 2018 to May 2020, covering two winter seasons and one summer.