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Article

There’s no reason a wood structure can’t last virtually forever – or, at least hundreds of years, far longer than we may actually need the building. With a good understanding of how to protect wood from decay and fire, we can expect today’s wood buildings to be around for as long as we wish.

While wood does not have the historical longevity of stone, there nonetheless remain standing some very old wood buildings. In Europe, wood was long a dominant building material dating back to the beginning of civilisation. Most of these ancient buildings are long gone, lost to fire, decay, or deconstruction for another purpose. In the early days of wood construction, the primary structural components were placed directly in the ground, which eventually leads to decay. It was not until sometime in the 1100s that builders began to use stone footings – thus our still-standing examples of wood buildings generally date from no earlier than that time.

Perhaps the most famous ancient European wood buildings still in evidence today are the Norwegian stave churches, hundreds of which were built in the 12th and 13th centuries and of which 25-30 still remain today. Their exterior claddings have typically been replaced, but the structural wood is original.

The Urnes stave church (c. 1150) in Sogn og Fjordane County is Norway’s oldest. Photo source

 

 

 

 

 

 

 

In North America, the abundance of wood and the existing timber skills of early settlers led to widespread use of wood – wood has always been and still is the primary structural material for small buildings here. The oldest surviving wood homes in the US date to the early 1600s. Nearly 80 homes remain from this era in the New England states.

The Fairbanks House (c. 1636) in Dedham, Massachusetts, USA, is the oldest surviving timber frame house in North America. It was built for Jonathan and Grace Fairebanke and was occupied by them and seven succeeding generations of the family until the early twentieth century. The Fairbanks family still owns the property. The house is open as a museum. Photo source.

 

 

 

 

 

 

 

Many other North American wood buildings survive from the 18th century. Even in the demanding climate of Louisiana, where hot and humid conditions present a challenge for wood durability, one can still find some of the original French settlements dating to the first half of the 1700s. And of course, there are countless standing wood buildings from the 1800s and early 1900s, most of which are probably still occupied.

The Parlange Plantation (c. 1750) in Pointe Coupée Parish, Louisiana, USA, was built by the Marquis Vincent de Ternant and remains in the possession of his descendants, the Parlange family. This large plantation home was constructed of bousilliage (mud, moss and deer hair) and cypress wood set over a hand-made brick raised basement. Photo source.

 

 

 

 

 

 

 

Japan has a well-known history of wood use and is the home of the oldest surviving wood structure in the world, a Buddhist temple near the ancient capital city of Nara. The Horyu-ji temple is believed to have been built at the beginning of the eighth century (c. 711) and possibly even earlier, as one of the hinoki (Japanese cypress) posts appears to have been felled in the year 594. This temple’s longevity is largely helped by careful maintenance and repair. This entire region of Japan has many other ancient wood buildings still standing.

 

The Horyu-ji temple at Nara

 

 

 

 

 

 

 

For modern buildings, we don’t normally require such exceptional longevity. The life of a typical North American house is no more than 100 years (the average is lower), and our non-residential buildings are usually demolished in 50 years or less. Wood is perfectly suitable for these lifetime expectations. Click here for survey data showing that wood buildings last as long, or longer than buildings made of other materials.

Reference:
Architecture in Wood: A History of Wood Building and Its Techniques in Europe and North America. Hans Jrgen Hansen, Ed., Faber and Faber, London, 1971..

Case Studies

1865 House, Vancouver BC

 

 

 

 

Irving House is a large, one and one-half storey plus basement wood-frame residence, designed in the Gothic Revival style, located on its original site at the corner of Royal Avenue and Merivale Street in the New Westminster neighbourhood of Albert Crescent. Irving House is remarkable for the extent to which its original exterior and interior elements have been maintained. Operated as an historic house museum, it also includes a collection of many original furnishings from the Irving family.

Irving House
Location 302 Royal Avenue, New Westminster, B.C.
Completion of Construction 1865
Other Information Original owner – Captain William and Elizabeth Jane Irving
Current Status Heritage of New Westminster
Construction Method Platform-Frame
Style Gothic Revival style
Framing 2-inch Douglas Fir lumber
Cladding Wide lapped Redwood weatherboard siding and wooden trim
Comdition No signs of decay on any framing members
Major Repair 1880

By courtesy of New Westminster Museum and Archives, New Westminster, British Columbia

Other link: http://www.flickr.com/photos/bobkh/297751638/in/set-72157594340707368/

1912 House, Vancouver BC

 

 

 

 

This classic turn-of-the-century home was slated for demolition in 1990. It was already stripped back to the bare framing when it was purchased by a new owner who wished to convert it into apartments. At the new owner’s request, the building was inspected by Dr. Paul Morris of Forintek in 1991 for signs of deterioration. After 80 years in service there were no signs of decay on any of the framing members nor the window frames, most of which were original.

1912 House
Location Vancouver
Date of Construction 1912 (estimated)
Original Records Water service 1909
On City File 1915
Other Information Original owner – Henry B. Ford
Current Status Vancouver Heritage Resource Inventory
Construction Method Platform-Frame
Style Heritage, with multiple pitched roofs & wide overhangs
Framing Rough green full 2-inch Douglas Fir lumber
Sheathing Rough green Douglas Fir boards
Building Paper Asphalt-impregnated paper
Cladding Western Red Cedar shakes
Western Red Cedar siding
Roofing Western Red Cedar shakes (new in 1991)
Condition No signs of decay on any framing members

Temple at Nara, Japan

The Horyuji Buddhist temple at Nara is probably the oldest wooden structure in the world. Nara became the first permanent capital of Japan in 710.

 

 

 

 

 

Horyuji Buddhist temple at Nara
Location Nara, Japan
Date of Construction 670 – 714 (Estimated)
Original Records Built on site of original temple from 607
Other Information Original owner – Prince Shotoku
Current Status World Cultural Heritage Building
Construction Method Heavy Timber
Style 2-inch Douglas-fir lumber
Framing Hinoki (Durable – Japanese cypress)
Roofing Multi-tiered roof with Clay tile
Condition No signs of decay on any framing members
Maintenance Schedule Major repairs every 100 years, rebuilt every 300 years
Article

Wood is resistant to some of the chemicals destructive to steel and concrete. For example, wood is often the material of choice when exposed to: organic compounds, hot or cold solutions of acids or neutral salts, dilute acids, industrial stack gases, sea air and high relative humidity. Because of its resistance to chemicals wood is often used in the following applications:

  • Potash storage buildings
  • Salt storage domes
  • Cooling towers
  • Industrial tanks for various types of chemicals

With thoughtful design and careful workmanship wood bridges prove to be remarkably durable. Throughout the world, there are numerous examples of long lasting wooden bridges – both historic and modern. Modern bridge decks are subjected to relentless attack of de-icing chemicals, and wood is gaining acceptance as a viable option for these applications.

Pilings that are constantly submerged in fresh water have been known to last for centuries. Foundation piles under structures will not decay if the water table remains higher than the pile tops. Many of the world’s important structures are built on wood piles including much of the city of Venice and the Empire State Building in New York.

Article

Studies

Reports

Fire Research

Acoustics Research and Guides

Tall Wood Building Demonstration Initiative Test Reports
(funding provided by Natural Resources Canada)

Visit Think Wood’s Research Library for additional resources

banner for research.thinkwood.com

Article

In the early 1900s, light-frame wood construction and heavy timber, up to ten-storeys in height, was commonplace in major cities throughout Canada. The longevity and continued appeal of these buildings types is apparent in the fact that many of them are still in use today. Over the past decade, there has been a revival in the use of wood for taller buildings in Canada, including mid-rise light-frame wood construction up to six-storeys in height.

Mid-rise light-frame wood construction is more than basic 2×4 framing and wood sheathing panels. Advances in wood science and building technology have resulted in stronger, safer, more sophisticated engineered building products and systems that are expanding the options for wood construction, and providing more choices for builders and designers. Modern mid-rise light-frame wood construction in incorporates well researched and safe solutions. The engineering design and technology that has been developed and brought to market is positioning Canada as a leader in the mid-rise wood-frame construction industry.

In 2009, via its provincial building codes, British Columbia became the first province in Canada to allow mid-rise buildings to be made from wood. Since this change to the British Columbia Building Code (BCBC), which increased the permissible height for wood frame residential buildings from four- to six-storeys, more than 300 of these structures have been completed or are underway with BC. In 2013 and 2015, Québec, Ontario, and Alberta, respectively, also moved to permit mid-rise wood-frame construction up to six-storeys in height. These regulatory changes indicate that there is clear market confidence in this type of construction.

Scientific evidence and independent research has shown that mid-rise wood-frame buildings can meet performance requirements in regard to structural integrity, fire safety, and life safety. That evidence has now also contributed to the addition of new prescriptive provisions for wood construction, as well as paved the way for future changes that will include more permissible uses and ultimately greater permissible heights for wood buildings. As a result of this research, and the successful implementation of many mid-rise wood-frame residential buildings, primarily in British Columbia and Ontario, the Canadian Commission on Building and Fire Codes (CCBFC) approved similar changes to the National Model Construction Codes. The 2015 edition of the National Building Code of Canada (NBC) permits the construction of six-storey residential, business, and personal services buildings using traditional combustible construction materials. The NBC changes recognize the advancements in wood products and building systems, as well as in fire detection, suppression, and containment systems.

In relation to mid-rise wood-frame buildings, several changes to the 2015 NBC are designed to further reduce the risks posed by fire, including:

  • increased use of automatic sprinklers in concealed areas in residential buildings;
  • increased use of sprinklers on balconies;
  • greater water supply for firefighting purposes; and
  • 90 percent noncombustible or limited-combustible exterior cladding on all storeys.

Most mid-rise wood-frame buildings are located in the core of smaller municipalities and in the inner suburbs of larger ones, offering economic and sustainability advantages. Mid-rise wood-frame construction supports the goals of many municipalities; densification, affordable housing to accommodate a growing population, sustainability in the built environment and resilient communities.

Many of these buildings have employed light-frame wood construction from the ground up, with a five- or six-storey wood-frame structure being constructed on a concrete slab-on-grade, or on top of a concrete basement parking garage; others have been constructed above one- or two-storeys of noncombustible commercial occupancy.

Mid-rise wood buildings are inherently more complex and involve the adaptation of structural and architectural details that address considerations related to structural, acoustic, thermal and fire performance design criteria. Several key aspects of design and construction that become more critical in this new generation of mid-rise wood buildings include:

  • increased potential for cumulative shrinkage and differential movement between different types of materials, as a result of the increased building height;
  • increased, dead, live, wind and seismic loads that are a consequence of taller building height;
  • requirements for continuous stacked shearwall layouts;
  • increased fire-resistance ratings for fire separations, as required for buildings of greater height and area;
  • ratings for sound transmission, as required for buildings of multi-family residential occupancy, as well as other uses;
  • potential for longer exposure to the elements during construction;
  • mitigation of risk related to fire during construction; and
  • modified construction sequencing and coordination, resulting from the employment of prefabrication technologies and processes.

There are many alternative approaches and solutions to these new design and construction considerations that are associated with mid-rise wood construction systems. Reference publications produced by the Canadian Wood Council provide more detailed discussion, case studies and details for mid-rise design and construction techniques.

 

For further information, refer to the following resources:

Mid-Rise Best Practice Guide (Canadian Wood Council)

2015 Reference Guide: Mid-Rise Wood Construction in the Ontario Building Code (Canadian Wood Council)

Mid-Rise 2.0 – Innovative Approaches to Mid-Rise Wood Frame Construction (Canadian Wood Council)

Mid-Rise Construction in British Columbia (Canadian Wood Council)

National Building Code of Canada

Wood Design Manual (Canadian Wood Council)

CSA O86 Engineering design in wood

Wood for Mid-Rise Construction (Wood WORKS! Atlantic)

Fire Safety and Security: A Technical Note on Fire Safety and Security on Construction Sites in British Columbia/Ontario (Canadian Wood Council)

Article

Studies

General

Structural & Seismic

Vertical Movement in Wood Platform Frame Structures (CWC Fact Sheets)

Design of multi-storey wood-based shearwalls: Linear dynamic analysis & mechanics based approach

Fire

Testing

Fire Research

Research for Wood and Wood-Hybrid Mid-Rise Buildings Project
National Research Council Canada (2011-2015)

Other Reports

Acoustics Research

Research for Wood and Wood-Hybrid Mid-Rise Buildings Project
National Research Council Canada (2011-2015)

Other Reports & Guides

Building Envelope Research

Research for Wood and Wood-Hybrid Mid-Rise Buildings Project
National Research Council Canada (2011-2015)

Visit Think Wood’s Research Library for additional resources

banner for research.thinkwood.com

Article

Timber bridges have a long history as vital components of the roadway, railway and logging road networks within Canada. Dependent on the availability of materials, technology, and labour, the design and construction of wood bridges has evolved significantly over the last 200 hundred years throughout North America. Wood bridges take on many forms and use alternative support systems; including simple span log bridges, different types of trussed bridges, and stress-laminated or composite bridge decks and components. Timber bridges remain an important part of our transportation network in Canada.

The benefits of building modern timber bridges include:

  • reduced initial cost, particularly for remote areas;
  • speed of construction, through the use of prefabrication;
  • sustainability advantages;
  • aesthetics;
  • lighter foundations;
  • lower earthquake loads, coupled with less complex connections to substructures;
  • smaller temporary structures and cranes; and
  • lower transportation costs associated with lower weight materials.

The different types of materials used to construct wood bridges include: sawn lumber, round logs, straight and curved glued-laminated timber (glulam), laminated veneer lumber (LVL), parallel strand lumber (PSL), cross-laminated timber (CLT), nail-laminated timber (NLT), and composite systems such as stress-laminated decks, wood-concrete laminated decks, and fibre-reinforced polymers.

Two main wood species used for wood bridge construction in Canada are Douglas fir and the Spruce-Pine-Fir species combination. Other species within the Hem-Fir and Northern species combinations are also recognized under CSA O86, however, they are less commonly used in bridge construction.

All metal fasteners used for bridges must be protected against corrosion. The most common method for providing protection is hot dip galvanizing, a process whereby a sacrificial metal is added to exterior of the fastener. Different fastener types that are used in wood bridge construction include, but are not limited to, bolts, lag screws, split rings, shear plates, and nails (for deck laminations only).

All highway bridges in Canada must be designed to meet the requirements outlined in CSA S6 and CSA O86. The CSA S6 standard requires that the main structural components of any bridge in Canada, regardless of construction type, be able to withstand a minimum of 75 years of loading during its service life.

The style and span of bridges varies greatly depending on the application. In hard to reach locations with deep valleys, timber trestle bridges were common at the end of the 19th century and into the beginning of the 20th century. Historically, trestle bridges relied heavily on ample timber resources and in some cases, were considered to be temporary. Initial construction of North America’s transcontinental railways would not have been possible without the use of timbers to construct bridges and trestles.

Many examples of trussed timber bridges for have been built for well over a century. Trussed bridges allow for longer spans compared to simple girder bridges and historically had spans in the range of 30 to 60 m (100 to 200 ft). Bridges that are designed with trusses located above the deck provide a great opportunity to build a roof over the roadway. Installing a roof overhead is an excellent way to shed water away from the main bridge structure and protect it from the sun. The presence of these covered roofs is the main reason these century-old covered bridges remain in service today. The fact that they remain part of our landscape is as much a testament to their hardiness as to their attractiveness.

Although originally devised as a rehabilitation measure for aging bridge decks, the stress-laminating technique has been extended to new bridges through the application of stressing at the time of original construction. Stress-laminated decks provide improved structural behaviour, through their excellent resistance to the effects of repeated loading.

Three main considerations related to durability of wood bridges include protection by design, preservative treatment of wood, and replaceable elements. A bridge can be designed such that it is inherently self-protecting by deflecting water away from the structural elements. Preservative treated wood has the ability to resist the effects of de-icing chemicals and attack by biotic agents. Lastly, the bridge should be designed such that, at some point in its future, a single element can be replaced relatively easily, without significant disruption or cost.

 

For further information, refer to the following resources:

Wood Highway Bridges (Canadian Wood Council)

Ontario Wood Bridge Reference Guide (Canadian Wood Council)

CSA S6 Canadian Highway Bridge Design Code

CSA O86 Engineering design in wood

Article

What do the experts have to say about wood-frame mid-rise construction?

Is mid-rise and tall wood building construction a new phenomenon:

Wood-frame and heavy timber construction (up to ten storeys) was the norm in the early 1900’s, and many of these buildings still exist and are in use in many Canadian cities.

Over the past 10 years, there is a revival in the use of wood for both mid-rise (up to six-storeys) and tall buildings. In British Columbia alone, as of December 2013, there were over 250 five- and six-storey wood product based mid-rise buildings either in the design or construction phase.

Why have code change proposals?

This 2015 building code change is not about favoring wood over other building materials; it’s about acknowledging, via the highly thorough code process, that science-based innovation in wood products and building systems can and will lead to more choices for builders and occupants.

Are these buildings safe?

Regardless of the building material in question, nothing gets built unless it meets code. Mid-rise wood-frame buildings reflect a new standard of engineering in that structural, fire and seismic concerns have all been addressed by the expert committees of the Canadian Commission on Building and Fire Codes. As an example, when it comes to concerns from firefighters, there is increased sprinkler protection for concealed spaces and balconies, greater water supply for fire protection, restrictions on types of building claddings used and increased consideration for access by firefighters . In the end,  when occupied, these buildings fully meet the same requirements of the Building Code as any other type of construction from the perspective of health, safety and accessibility.

What are some of the new safety provisions being proposed?

Fire safety:

  • Increased level of sprinkler / water protection:
  • More  concealed spaces sprinklered
  • Balconies must be sprinklered
  • Greater water supply for fire protection
  • Non-combustible or limited combustible exterior wall cladding on 5th and 6th storey
  • 25% of perimeter must face one street (within 15m of street) for firefighter access

Seismic and wind provisions:

  • Similar to BC Building Code
  • Guidance (Appendix) on impact of increased rain and wind loads for 5- and 6-storey

Acoustics:

  • Requirements for Apparent Sound Transmission Class (ASTC)
  • Supported by science from FPInnovations, NRC and many others.

Doesn’t wood burn?

No building material is impervious to the effects of fire. The proposed code changes go above and beyond the minimum requirements outlined in the NBCC. Health, safety, accessibility, fire and structural protection of buildings remain the core objectives of the NBCC and wood industry at large.

What about construction site safety?

The Canadian Wood Council has developed construction site fire safety guides which outline best practices and safety precautions to take during the construction phase of a building.

Are mid-rise wood-frame buildings cost effective?

For the most part, yes. Mid-rise wood-frame buildings are often a less expensive construction option for builders. This is good news for main-street Canada where land is so expensive. The recommended changes to the National Building Code of Canada (NBCC) would give the opportunity to erect safe, code compliant buildings that would otherwise not be possible. The net benefit of reduced construction costs is increased affordability for home buyers. In terms of new economic opportunity, the ability to move forward “now” creates new construction jobs in cities and supports employment in forestry communities. This also offers increased export opportunities for current and innovative wood products, where adoption in Canada provides the example for other countries.

Article

On behalf of the Canadian Commission on Building and Fire Codes (CCBFC) the National Research Council (NRC) Codes Canada publishes national model codes documents that set out minimum requirements relating to their scope and objectives. These include the National Building Code (NBC), the National Fire Code (NFC), the National Energy Code for Buildings (NECB), the National Plumbing Code (NPC) and other documents. The Canadian Standards Association (CSA) publishes other model codes that address electrical, gas and elevator systems.

The NBC is the model building code in Canada that forms the basis of most building design in the country. The NBC is a highly regarded model building code because it is a consensus-based process for producing a model set of requirements which provide for the health and safety of the public in buildings. Its origins are deeply entrenched within Canadian history and culture and a need to house the growing population of Canada safely and economically. Historical events have shaped many of the health and safety requirements of the NBC.

Model codes such as the NBC and NECB have no force in law until they are adopted by a government authority having jurisdiction. In Canada, that responsibility resides within the provinces, territories and in some cases, municipalities. Most regions choose to adopt the NBC, or adapt their own version derived from the NBC to suit regional needs.

The model codes in Canada are developed by experts, for experts, through a collaborative and consensus-based process that includes input from all segments of the building community. The Canadian model codes build on the best expertise from across Canada and around the world to provide effective building and safety regulations that are harmonized across Canada.

The Codes Canada publications are developed by the Canadian Commission on Building and Fire Codes (CCBFC). The CCBFC oversees the work of a number of technical standing committees. Representing all major facets of the construction industry, commission members include building and fire officials, architects, engineers, contractors and building owners, as well as members of the public. Canadian Wood Council representatives hold membership status on several of the standing committees and task groups acting under the CCBFC and participate actively in the technical updates and revisions related to aspects of the Canadian model codes that apply to wood building products and systems.

During any five-year code-revision cycle, there are many opportunities for the Canadian public to contribute to the process. At least twice during the five-year cycle, proposed changes to the Code are published and the public is invited to comment. This procedure is crucial as it allows input from all those concerned and broadens the scope of expertise of the Committees. Thousands of comments are received and examined by the Committees during each cycle. A proposed change may be approved as written, modified and resubmitted for public review at a later date, or rejected entirely.

 

For further information, refer to the following resources:

Fire Safety Design in Buildings (Canadian Wood Council)

Codes Canada – National Research Council of Canada

National Building Code of Canada

Article

The current edition of the National Building Code of Canada (NBC) is published in an objective-based format intended to allow more flexibility when evaluating non-traditional or alternative solutions. The objective-based format currently in use provides additional information that helps proponents and regulators determine what minimum performance level must be achieved to facilitate evaluation of new alternatives. Although the NBC helps users understand the intent of the requirements, it is understood that proponents and regulators will still have a challenge in terms of demonstrating compliance. In any case, objective-based codes are expected to foster a spirit of innovation and create new opportunities for Canadian manufacturers.

Requirements related to the specification of structural wood products and wood building systems that relates to health, safety, accessibility and the protection of buildings from fire or structural damage is set forth in the NBC. The NBC applies mainly to new construction, but also aspects of demolition, relocation, renovation and change of building use. The current NBC was published in 2015, and is usually updated on a five-year cycle. The next update is expected in 2020.

In terms of structural design, the NBC specifies loads, while material resistance is referenced through the use of material standards. In the case of engineering design in wood, CSA O86 provides the designer with the means of calculating the resistance values of structural wood products to resist gravity and lateral loads. Additional design information is found in the companion documents to the NBC; Structural Commentaries (User’s Guide – NBC 2015: Part 4 of Division B) and the Illustrated User’s Guide – NBC 2015: Part 9 of Division B, Housing and Small Buildings.

In Canada, structural wood products are specified prescriptively or through engineered design, depending on the application and occupancy. Design professionals, such as architects and engineers, are generally required for structures that exceed three-storeys in height or are greater than 600 m2 or if occupancies are not covered by Part 9 ‘Housing and Small Buildings’ of the NBC.

Housing and small buildings can be built without a full structural design using prescriptive requirements found in Part 9 of the Code. Some Part 9 requirements are based on calculations, others are based on construction practices that have a proven performance history. Generally prescriptive use is allowed if the following conditions are met:

  • three-stories or less
  • 600m2 or less
  • uses repetitive wood members spaced within 600 mm
  • spans are less than 12.2 meters
  • floor live loads do not exceed 2.4 kPa
  • residential, office, mercantile or medium-to low-hazard industrial occupancy

The rationale for not basing all Part 9 requirements on calculations comes from the fact that there has been historical performance and experience with small wood-frame buildings in Canada, in addition to the notion that many of the non-structural elements actually contribute to the structural performance of a wood-frame system. Quantifying the ‘system’ effects on overall behaviour of a wood-frame building cannot be done adequately using typical design assumptions, such as two-dimensional load paths and single member engineering mechanics. In these instances, the requirements for houses and small buildings is based on alternative criteria of a prescriptive nature. These prescriptive criteria are based on an extensive performance history of wood-frame housing and small buildings that meet current day code objectives and requirements.

Buildings that fall outside of prescriptive boundaries or are intended for major occupancy or post disaster situations must be designed by design professionals in accordance with Part 4 of the NBC. Structural resistance of wood products and building systems are engineered according to the requirements of CSA O86 in order to resist the loadings described in Part 4 of the NBC.

 

The following CWC publications are reference in the NBC:

Moisture and Wood-Frame Buildings

Introduction to Wood Building Technology

Wood Reference Handbook

The Span Book

Engineering Guide for Wood Frame Construction

 

For further information, refer to the following resources:

Fire Safety Design in Buildings (Canadian Wood Council)

Codes Canada – National Research Council of Canada

National Building Code of Canada

CSA O86 Engineering design in wood

Article
Article

Wood has been a valuable and effective structural material since the earliest days of human civilisation. With normal good practice, wood can deliver many years of reliable service. But, like other building materials, wood can suffer as a result of mistakes made in storage, design, construction, and maintenance practices.

How can you ensure long life of a wood building? The best approach is always to remember that wood meant for dry application must stay dry. Start out by buying dry wood, store it carefully to keep it dry, design the building to protect the wood elements, keep wood dry during construction, and practice good maintenance of the building. This approach is called durability by design.

If wood won’t stay dry, you have two choices in approach. Because wet wood is at risk of decay, you must select a product with decay resistance. One choice is to choose a naturally durable species like Western red cedar. This approach is called durability by nature.

Most of our construction lumber is not naturally durable, but we can make it decay resistant by treating it with a preservative. Preservative-treated lumber is more reliably resistant to decay than naturally durable lumber. This approach is called durability by treated wood.

The level of attention you give to durability issues during the course of design depends on your decay hazard. In other words, the more that your circumstances put wood at risk, the more care you must take in protecting against  decay. In outdoor applications, for example, any wood in contact with the ground is at high risk of decay and should be pressure-treated with a preservative. For wood that is exposed to the weather but not in direct ground contact, the degree of hazard correlates with climate. The fungi that harm wood generally grow best in moist environments with warm temperatures. Researchers have developed hazard zones in North America using mean monthly temperature and number of rainy days. This map in particular shows the rainfall hazard and applies to exposed uses of wood such as decks, shingles and fence boards. A high degree of hazard would indicate a need to carefully choose a wood species or preservative treatment for maximum service life. In the future, building codes may provide more specific directives as a function of decay hazard. For wood not exposed to weather, such as framing lumber, this map is only moderately useful. This is because the environmental conditions in the wall may be substantially different than those outdoors.

Article

Wood Storage And Handling

Wood is a long-lasting, economical and renewable resource that is the building material of choice for North American housing. This is due, in large part, to the proven performance of properly designed and constructed wood-frame buildings that have provided strong and lasting housing for many people. Although wood can withstand much, attention must be paid to storage and handling in order for the material to perform according to expectations. Managing moisture in structural wood products is essential to controlling the swelling and shrinkage of the wood and in the prevention of problems directly associated with such contact.

On Site Moisture Management

Moisture management during construction has become more and more important with the increase in building height and area (which potentially prolongs the exposure to inclement weather), and the overall increase in the speed of construction which may not allow adequate time for drying to occur. In addition, the drying capacities of modern assemblies may have reduced resulting from increased insulation levels to meet more stringent energy efficiency requirements, or the use of membrane or insulation products with low vapour permeance. Adequate on-site moisture protection is challenging given the range of possible moisture exposure conditions and the inevitable site and cost constraints of a construction project.

More Information

 

 

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  • Saint Vincent and the Grenadines+1
  • Samoa+685
  • San Marino+378
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