Wood products

Wood has many attributes that make it a smart environmental choice. It's the only major building material that's renewable and sustainable over the long term and it's a natural choice when it comes to climate change, for three important reasons:

1. Wood products continue to store the carbon sequestered by trees.

In the section on forests and carbon, we highlighted the capacity of forests to act as carbon sinks. When trees are converted into wood products, such as furniture and homes, much of the sequestered carbon is stored in those products indefinitely-which keeps it out of the atmosphere. The graphic below shows the combined impact over time including the CO₂ emissions avoided by substituting the wood for energy intensive building products like steel or concrete.

2. Using more wood use means less fossil fuel consumption.

Life cycle assessment studies show that wood requires substantially less energy to manufacture, transport, construct and maintain than other materials. Most notable is the significant volume of greenhouse gas emissions avoided by substituting low impact wood products for materials such as concrete, which are responsible for high amounts of CO₂ emissions.

3. Wood products are durable and adaptable.

After decades or even centuries of use, wood buildings can be easily adapted or deconstructed and reused, which means they can continue to store carbon indefinitely.

By using wood instead of energy-intensive materials such as steel, concrete or plastics, society can significantly reduce its reliance on fossil fuels and its greenhouse gas emissions.

Life Cycle Assessment

Life cycle assessment (LCA) is an objective way to compare materials, assemblies and even whole structures, over the course of their entire lives, from resource extraction through manufacturing, distribution, use and end-of-life disposal. It has been widely used to compare the environmental impacts of building materials such as wood, steel and concrete, and scientists in Europe and North America have come to the same conclusion: compared to the alternatives, wood buildings produce less air and water pollution, require less energy across their life cycle, and generate less CO₂ emissions.

The Consortium for Research on Renewable Industrial Materials (CORRIM) has conducted various studies on the impacts of forests and wood products on carbon emissions and sequestration. One study used LCA to compare homes framed with wood and steel in Minneapolis and homes framed with wood and concrete in Atlanta-the framing types most common to each city. In both cases, the wood-frame homes performed substantially better than their non-wood counterparts. According to the report, the homes framed in steel and concrete required 16 and 17 per cent more energy respectively (from extraction through maintenance) than the wood-frame homes. The global warming footprint of the steel-frame house was also 26 per cent higher and the concrete-frame house 31 per cent higher than the homes framed in wood.

Another study, conducted by the Canadian Wood Council, compared the life cycle impacts of three 2,400 square foot homes designed primarily in wood, steel and concrete over the first 20 years of their lives. Relative to wood, the steel and concrete homes were predicted to:

• Require 26 percent and 57 percent more energy (from extraction through maintenance)
• Emit 34 percent and 81 percent more greenhouse gases.

If there was any doubt that buildings and products made from wood have a lighter carbon footprint, the scientific study of life cycle assessment has now firmly established wood as a climate change solution.

Energy Efficiency

Wood contributes to energy efficiency in three important ways-reduced embodied energy, reduced operating energy and as an alternative energy source to fossil fuels-all of which translate into less greenhouse gas emissions.

Embodied energy – This is the sum of the energy required to extract, harvest, process, manufacture, transport, construct and maintain the materials/products used in building applications. This "embodied" energy, though less significant in quantity than the amount of energy consumed by ongoing building operations, nevertheless impacts upon the environment and plays an important role in environmental assessment.

Comparing embodied energy using life cycle assessment, the Canadian Wood Council found that steel and concrete building designs embody 26 per cent and 57 per cent more energy relative to a comparable wood design. Because wood is lighter than the alternative materials, transportation energy is significantly less. When extracted from the natural environment, wood is in a ready-to-use state and requires very little manufacturing relative to steel and concrete, which have to change form and require substantially greater inputs of chemicals, water and energy before they are ready for use in a building.

This data was generated in Europe and shows the life cycle CO₂ emissions of different building materials. The CO₂ absorbed by growing forests and stored in wood products offsets the energy required to harvest, process, transport and maintain those products over time, which is why their net emission are below zero.

The heating and cooling of homes accounts for 50 per cent of all utility costs (gas, oil, hydro-electric) and about 15 per cent of all energy used in North America. Because wood is 400-times less heat conductive than steel and 8.5 times less conductive than concrete, homes built with wood framing are easier to insulate. Wood's cellular structure contains air pockets which limit its ability to conduct heat and help to minimize the energy needed for heating and cooling.

The unique adaptability of wood construction in combination with the superior insulating capability of wood framing means that wood can meet the most demanding energy codes with less cost.

Durability and Adaptability

The world is full of examples of ancient, wood-frame buildings that remain structurally sound-such as Norway's beautiful Stave churches, which were built hundreds of years ago and are still in use today. In fact, extended service life is one of the key advantages wood offers as a building material.

In a survey of buildings demolished between 2000 and 2003 in Minneapolis/St. Paul, for example, wood buildings had the longest life spans. Sixty-three percent of the demolished wood buildings were older than 50 years at demolition and the majority were older than 75. By comparison, over half of the demolished concrete buildings fell into the 26-50 year category and only one third of the concrete buildings lasted more than 50 years. Similarly, 80 per cent of the steel buildings demolished fell below the 50-year mark, and half of those were no older than 25 years.

However, the study also concluded that there is no significant relationship between the structural system used and the actual life of the building. Reasons for demolition were instead related to changing land values, a building's lack of suitability for current needs, and lack of maintenance of various non-structural components. In fact, the survey found that developers demolish most buildings well before the end of the useful life of their structural framing, which brings us to another of wood's advantages-adaptability.

After decades or even centuries of use in one capacity, wood beams can be reused either intact or resized. And, unlike steel, plastic or masonry, wood requires little or no energy to achieve its new beginning.

Source: Survey on Actual Service Lives for North American Buildings – FPInnovations – Forintek Division