Wood has a lower thermal conductivity compared to concrete, steel-frame and masonry construction and is ideally suited to energy-efficient design. As a natural insulator, it provides some of the world’s coldest climates with warm and comfortable dwellings.
Wood is used in the vast majority of single-family homes and multi-family projects up to six storeys in Canada and for good reason—it’s adaptable to virtually any climate, can be tailored to handle wind and snow loads and is a natural insulator reducing heating and cooling costs. Softwood has about 10 times the thermal insulating ability of concrete and masonry, and 400 times that of solid steel. Unlike concrete and steel, wood’s natural insulating qualities mean it does not need a thermal break between the structural and exterior envelope.
New energy codes and standards mean wood construction is getting even more energy efficient. Wood and light-frame construction’s versatility offers more insulation options not readily available for other construction types. This includes deeper wall cavities, increased thermal mass, wood-fibre panels and installation outside the framing spaces.
Vancouver Island Mountain Centre | Photo credit: Bob Matheson, courtesy of HDR
Prefabrication of wood buildings in factory settings can further improve thermal performance by delivering a precise fit that is tested and airtight. With these new approaches, wood buildings are meeting and exceeding the requirements of new energy and voluntary programs, such as Passive House.
Passive House (Passivhaus) is considered to be the most rigorous voluntary energy-based standard in the design and construction industry today. It is a holistic approach to energy efficiency that considers all aspects of a structure. This includes data on local weather and solar orientation along with design, foundation, framing, and insulation systems to reduce or even eliminate thermal bridging. This means using building materials that have low thermal conductivities.
By nature, wood is ideal for this, made up of thousands of open cells that make it difficult to conduct heat. Furthermore, highly energy efficient, airtight buildings can be achieved using prefabricated timber building systems cut and assembled with precision within a controlled environment. Unnecessary framing is eliminated and replaced with insulation to optimize energy performance. Dense recycled wood fibre panels can replace conventional insulation while providing sound reduction while boosting thermal mass.
BC Passive House Factory | Photo credit: Ema Peter Photography
High-performance wood construction and the BC Energy Step Code can help meet that goal. The Step Code offers an optional compliance path in the BC Building Code that local governments use to incentivize or require a level of energy efficiency in new construction that goes above and beyond the requirements of the BC Building Code.
UBC Campus Energy Centre | Photo credit: Ema Peter Photography
Mass timber construction uses large prefabricated wood members such as cross-laminated timber (CLT) for wall, floor and roof construction. Glue-laminated timber (glulam) can also be used as beams and columns. Like all wood products, mass timber has good thermal properties and the added thickness provides both insulation and thermal mass. While thermal mass is typically associated with concrete or masonry buildings; mass timber has considerable thermal mass that can offer some whole-building energy benefits.
One example is the University of Northern British Columbia’s Wood Innovation Research Lab (WIRL), the first industrial facility tested and certified to the International Passive House standard in Canada. Constructed using a glulam post and beam system and unique high-performance standing truss wall assembly, the building serves as a research and testing facility for University faculty and students. Sophisticated sensors and thermal monitoring showed significant energy savings.
For projects targeting net-zero energy or other stringent energy performance criteria, mass timber can store solar heat energy during the day and release it at night, reducing energy loads. Hybrid building systems, combining mass timber, concrete or masonry can further boost the energy efficiency of wood buildings.
Wood Innovation Research Lab | Photo credit: Michael Elkan Photography
Mass timber combined with masonry cladding gives the Ronald McDonald House BC & Yukon significant thermal mass and a boost to its energy efficiency. The home-away-from-home for sick kids and their families is built of a hybrid CLT wall and high-performance light-wood floor system and clad with iron-spot brick façade.
Photo credit: Ed White Photographics
