| Natural Resources & Sustainability |
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Environmentally Friendly Homes
by Adam Downing
September 2008
If the 3 little pigs where building houses today, what would they choose to build with?
What is an environmentally friendly home that will stand the test of time? Some would say it is a home that was designed to use natural systems such as sun in the winter and shade in the summer or perhaps even geothermal energy to limit reliance on electricity and fossil fuels for home comfort. Indeed these, and other factors such as energy efficient appliances, are; in fact, part of a design that limits a home's impact on the environment. But builders of truly environmentally friendly homes need also consider what the home is actually made of. What’s holding it together?
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| Wood is an environmentally friendly choice when it comes to building a house. |
Home building material options come roughly in three categories. Wood, concrete or steel are the main building blocks of houses today. As building materials, each of these have certain benefits and drawbacks. Each also have environmental costs. Consideration must be given to what it takes to get a load of 2x4’s, concrete or steel framing to build a wall. From where do these raw materials come? How available are they? What does it take to extract and process these materials to provide us with useable building material?
Wood, concrete and steel are end products, processed from various natural resources. Wood, of course, comes from trees. Concrete is a mixture of sand, gravel and cement, which is made of burned lime and clay. Like concrete, steel also comes primarily from below the earth with the mining of iron-ore, which is then alloyed together with other materials to get certain properties. While each of these materials are extracted and processed differently, the environmental friendliness of each can be measured by keeping track of the total energy inputs for the product, from cradle to grave. The amount of energy required is a quantifiable tool to measure environmental impact.
Common sense suggests that if non-wood materials are used in place of wood, fewer trees have to be cut down. While demand for wood products does affect timber harvesting, the results of using other products have greater environmental costs. Steel ranks as the greatest energy consumer, with concrete second and wood as the least energy-demanding product to procure and process. Numerous studies have quantified this.
In the part of the world where one study was conducted, a typical steel house has a steel frame and corrugated iron roof with a concrete floor, brick veneer wall cladding and aluminum window frames. In actuality, the fraction of this house in steel is only 6% by weight but consumes up to 31% of the total energy! A house such as this requires approximately 525 units of energy measured in billions of Joules (GJ).
A typical concrete house ranks second, totaling almost 400 GJ. The concrete in this house accounts for approximately 26% of the total energy consumed.
A typical wood house (defined as a house where wood requires the largest percentage of energy of the 3 materials used) ranks #1 in the amount of energy required to produce the building materials. The energy used to produce the wood used in a typical wood house totals less than 20% of the total energy required for the materials in that house. Overall, a wood house requires just over 300GJ to produce. This is greater than 10% savings in total energy in production when compared to a concrete house and savings of almost 40% when compared to a steel house! This means that wood is the most environmentally friendly building material if consideration is given to how much energy it takes to get and process various materials.
Not only is wood easier to produce in terms of total energy to process, but it also comes from a natural resource which is renewable! As was mentioned earlier, all three products originate from natural resources. Natural resources fall into one of two broad categories, renewable and non-renewable. Renewable resources, as the name suggests, are renewable. That is, within a reasonable time frame (a generation or two), the resources we harvest can be replenished. The best and most pure example of renewable natural resources is forests.
Non-renewable natural resources, on the other hand, cannot be replenished within a reasonable time frame. Materials such as iron and concrete are examples of products that come from primarily non-renewable resources. When sand and gravel are mined from an area, it will not be replenished by natural systems except in geologic time (thousands and millions of years). The same is true for iron-ore, the primary ingredient in steel, we can not to back to an area and get more in a few years unless there was more there to begin with.
Trees, as natural resources, grow very fast. Trees can be harvested for use in our homes and offices and more trees will grow. With a little bit of management, we can even encourage faster and better growth! Depending on the type of trees, a new stand ready for harvest can grow from the ground up in as little as 15 years to as great as 100+ years. Even at this upper end, wood is a very renewable resource!
Wood, concrete and steel are all acceptable building materials in terms of strength and durability. But they are not created equal in terms of the impact to the environment. If the 3 little pigs where building houses today, what do you think they ‘WOOD’ choose?
Data from:
Goover J., D.O. White, and T.A.G. Langrish. 2002. Wood versus concrete and steel in house construction: A life cycle assessment. Journal of Forestry 100(8)34-41
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