July 8, 2008

Greener buildings in our future

What is the most environmentally sustainable construction material available for erecting homes and buildings? If net carbon emissions per ton of material is the key measurement, the answer is framing studs and medium density fiberboard made from wood.

That is one of the key messages from a new issue of Eco-link, a publication of the Temperate Forest Foundation's Research and Education division, which focuses on Consumer Choices; Greening Your Purchases.

How much more efficient is wood over the other materials when all steps in their manufacture is taken into consideration? Taking a look at the following chart from the U.S. Environmental Protection Agency gives us the answer to this question.

At the extreme, virgin aluminum requires 137.3 times more carbon emissions per ton of material than wood.

Of course every material has its specific uses. You wouldn't build a skyscraper with wood beams and little glass. But with new Leadership in Energy and Environmental Design LEEDs® rating systems receiving much more prestige among builders, any material that raises energy efficiency while lowering its carbon materials footprint is going to garner more ratings credit.

Combined with the insulation superiority of wood over other more modern materials (steel and glass) that require much more energy to heat and cool, wood would appear to be on the verge of making a comeback.

Joseph Lstiburek, Ph.D., P.Eng., is a principal of Building Science Corporation LLC and an ASHRAE Fellow. He has twenty-five years of experience in design, construction, investigation, and building science research. Through the Department of Energy's Building America program, Dr. Lstiburek has forged partnerships with designers, builders, developers, materials suppliers and equipment manufacturers to build higher performance homes across the U.S. His company specializes in building homes that require less energy to heat and cool. Their designs utilize wood for structural support and fiberboard sheathing of surfaces. His presentations include one that advocates that Wood is Good.

Climate-specific design and construction of high performance homes is a cornerstone of all BSC work. We recently modified both our criteria and our North American map for the hygro-thermal regions. The changes are not drastic but they are important because they make our criteria and map align with the International Energy Conservation Code (IECC) Climate Zones as developed by the Department of Energy. Whenever the building science community and the code community get on (literally) the same page, this is good news for builders of any homes, but particularly those that build climate-tuned, high performance homes.

Treated wood in an assembly performs better in a fire than steel studs, and wood is not thermally conductive. Don't believe me? Visit New Zealand and Australia and check out some of their 10- and 20-story buildings. They use concrete structural frames and treated wood frame wall infill assemblies with gypsum board linings on the inside and outside of the wood frame assembly covered with open rain screen vented fiber cement panels. These structures are exceptionally energy efficient, low cost and sustainable.

Sustainable management of wood resources, with forests being a significant part of the carbon sequestration equation, will play and increasingly important role in our climate change future.

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