Designing durable, enduring light-frame wood and mass timber buildings.
Prince George Airport Expansion
Photo: Michael Green
Wood structures are built to last
From thousands-year old wood buildings that have stood the test of time to modern tall timber towers rising ever higher, wood structures are strong and durable.
Wood buildings endure for centuries
Durable and strong, wood is a resilient material that provides decades, even centuries, of service. Yet misperceptions still exist that buildings made of materials such as concrete or steel last longer than buildings made of wood. As with any structural material, effective design is what counts.
Ancient wood buildings continue to stand including 8th century Japanese temples, 11th century Norwegian stave churches, and the many medieval post-and-beam structures of England and Europe. Beyond their cultural significance, these old wood buildings endure because they were well-designed, built and maintained.
Lom stave church, Norway
Photo: Arvid Høidahl
What's old is new again
With proper design and maintenance, wood structures provide long and useful service. And while durability is an important consideration, it’s often other factors, such as the ability to flex and adapt to new uses, that dictate the lifespan of a building. In fact, one study found no significant relationship between the structural system used and the actual life of the building. Property sales, changing occupant needs and rezoning are more frequently the reason a building is demolished. As a durable, reusable and recyclable material, wood can reduce waste and adapt to shifting needs.
Slack Headquarters, Vancouver
Photo: courtesy Leckie Studio Architecture + Design
How do trees stand so tall without falling over?
A tree is so strong that the sheer force of high winds, in most cases, doesn’t snap its trunk and branches. This natural strength is the result of the innate properties of wood. Wood is flexible enough that it won’t shatter, it’s stiff enough that it won’t break, it’s light enough that it won’t buckle under its own weight. As one scientist writes, “no manufactured material could do all of these things: plastics are not rigid enough; bricks are too weak; glass is too brittle; steel is too heavy. Weight for weight, wood has probably the best engineering properties of any material, so it is not surprising that we still use more wood than any other material to make our own structures.”
Wood is a naturally strong, lightweight material. Trees can tolerate great forces inflicted by wind, weather and even natural disasters. This is possible because wood is made up of long, thin strong cells. It is the unique elongated design of these cell walls that gives wood its structural fortitude. Cell walls are made of cellulose, lignin and hemicellulose. When converted to wood products, these cells continue to deliver lightweight, nimble structural solutions with the strength comparable to other building materials.
Consequently, despite their lighter weight, wood products can withstand considerable force—particularly when compression and tension forces are exerted parallel to the wood’s grain. For example, a single Douglas-fir square, 10 cm x 10 cm, can support nearly 5,000 kg in compression parallel to the grain. As a building material, wood performs well under stress as it’s a stiff material—how far it will bend before wear or failure. Wood is better for structures where the stress is constant and regular, making it a good choice for structures that bear high loads for a long time.
FOR THE LONG HAUL
Engineered wood is a good choice for exterior applications
More than a decade old, the exposed wood in the Brentwood Town Centre Stationlooks virtually new. To keep it performing and looking great the team used only kiln dried or engineered wood and designedthe station’s structure in such a way as toweather-proof the wood through deflection and drainage.
Brentwood Town Centre Station, Burnaby
Photo: Nic Lehoux
Deflection, drainage, drying and durability of wood buildings
Issues such as decay and mold can be avoided with proper detailing of wood buildings to prevent exposure to water and moisture entrapment. Moisture can be managed, and decay averted in wood buildings using four common strategies: deflection, drainage, drying and durable materials.
Deflection and drainageare thefirst lines of defense.Deflection devices (such as cladding and window flashings) intercept snow, rain and other sources of moisture at the building exterior and deflect it away from critical areas.Drainage ensures any penetration of water is removed to the exterior of the structure as quickly as possible, such as adrainage cavityintegrated into rainscreen walls.
Drying relates to venting, airflow and the breathability of a wood building.Today’s high performing timber buildings can achievesignificantairtightness while remaining permeable. In this scenario, moisture is diffused to the outsideminimizing the risk of condensation and mold growth while enhancing thermal performance.
Whistler Olympic Park
Photo: KK Law
A balancing act
Why is wood a good choice for humid environments?
With appropriate design, many wood products and species are resistant to high humidity and to many of the chemicals and conditions that adversely affect other materials, such as corrosive salts, dilute acids, industrial gases and sea air. Because of its resistance to these factors, wood is often well-suited for buildings with higher levels of humidity and moisture such as aquatic facilities. Wood is hygroscopic—that means it will constantly exchange moisture with the surrounding air—helping to control moisture and balance indoor humidity. Wood structures in humid environments, such as aquatic facilities, will resist shrinkage or warping due to moisture.
Along with deflection, drainage and drying, wood’s natural durability is an additional line of defense. British Columbia’s forests offer naturally durable species including western red cedar,yellow cedar and Douglas-fir.These species offer varying degrees of resistance to insects and decay in their natural state, due to high levels of organic chemicals called extractives. Extractives are naturally occurringchemicals that are deposited in the heartwood of certain tree species as they convert sapwood to heartwood. Such species are well suited to exterior uses such as siding, decking, fencing roofs and window framing—sometimes even used in boat making and marine uses due to their natural durability.
Wood structures provide long-lasting performanceand the use ofcareful detailing ofteneliminates the need for chemical treatments. In some cases, when wood isexposed and in continual contact with water—such as exterior decking or siding—or used in regions prone to wood-boring insects, additional measures may be needed.This can include the use of preservatives and high-pressure treatments to provide further resistance to decay. Increasingly, designers are turning to innovative design solutions andmore natural treatments for wood that reduce or avert the use of chemical preservatives.
Four Host First Nations Pavilion, Vancouver
Photo: KK Law
Deep lustrous charcoal offers beauty and brawn
The Wood Innovation and Design Centre, a tall wood demonstration project, is clad in naturally weathered and charred western redcedar—a protective technique that originated in Japan in the 18th century called shou sugiban. Sought after for its unique aesthetic, the process renders it a deep lustrous charcoal black while giving it added resilience to insects, fire and weather.
Wood Innovation and Design Centre, Prince George