Here are some interesting numbers from the Binational Softwood Lumber Council (BSLC) on the environmental footprint of building three similar homes from three three different materials – wood, metal and concrete. I’m sure you can guess what their numbers show: that wood is the greenest option.
I don’t know whether their numbers are based in reality or simply green-washing by the timber industry (I suspect the later), but either way for a small New York green contractor like Eco Brooklyn these numbers mean very little.
The BSLC is calculating numbers based on new raw materials to build new homes – the most wasteful kind of construction. Arguing whether new wood is better than new metal or new concrete is like arguing whether it is greener to fly via private jet or private helicopter.
They are stuck in an era that no longer exists:
True green building does not use new materials or build new buildings in the first place. If you are Eco Brooklyn you build with reused old materials to renovate existing homes – the most ecological kind of reconstruction.
The environmental footprint of using new materials to build new houses is like buying with your credit card. You are using up natural resources to create something that won’t last. But if you take a piece of wood out of the dump and use it to make an existing house last longer you are doing something different: you clean up the world on both ends of the production chain – both at the dump and in the home.
With this green building you actually create a negative environmental footprint in that you help reverse the impact of building on the planet. Instead of spending with credit you put cash into the bank as future savings.
Nonetheless here is their justification of using soft wood over metal or concrete with their sources below. Maybe somebody wants to look into it and see how valid the numbers are.
The chart below illustrates how each of the designs performed against five key indicators of environmental impact. With two exceptions, the wood-framed homes performed substantially better than their non-wood counterparts. The steel design produced slightly less solid waste and there was no significant difference in emissions to water in Atlanta.
MINNEAPOLIS DESIGN Wood Steel Difference (% Change) Embodied Energy (GJ) 651 764 113 17% Global Warming Potential (CO2 kg) 37,047 46,826 9,779 26% Air Emission Index (index scale) 8,566 9,729 1,163 14% Water Emission Index (index scale) 17 70 53 312% Solid Waste (total kg) 13,766 13,641 -125 -0.9%
ATLANTA DESIGN Wood Concrete Difference (% Change) Embodied Energy (GJ) 398 461 63 16% Global Warming Potential (CO2 kg) 21,367 28,004 6,637 31% Air Emission Index (index scale) 4,893 6,006 1,114 23% Water Emission Index (index scale) 7 7 0 0% Solid Waste (total kg) 7,442 11,269 3,827 51%
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:
- Release 24 percent and 47 percent more air pollution
- Produce 8 percent and 23 percent more solid waste
- Use 11 percent and 81 percent more resources
- Require 26 percent and 57 percent more energy (from extraction through maintenance)
- Emit 34 percent and 81 percent more greenhouse gases
- Discharge 4 and 3.5 times more water pollution
These differences may seem small until one realizes that only a small portion of the materials in a house (by weight) are involved in framing. One can expect the impacts to be many times greater when components made from different materials are compared directly.
- The Environmental Performance of Renewable Building Materials in the Context of Residential Construction
Consortium for Research on Renewable Industrial Materials (CORRIM), 15 pages
- Energy and the Environment
Canadian Wood Council, 16 pages
- The Athena Institute
Offers the ATHENA® EcoCalculator for Assemblies, which provides free LCA results for more than 400 common building assemblies as well as its parent tool, the ATHENA® Impact Estimator for Buildings
- National Institute for Standards and Technology
Product-focused, offers the BEES® LCA software (Building for Environmental and Economic Sustainability)
- Life Cycle of Wood Products
Canadian Wood Council, 1 page
- Wood and Green Building: The Role of Life Cycle Assessment
Wood Promotion Network, 2 pages