Air pollution emissionssuch as sulphur dioxide, nitrous oxides, methane, particulate and volatile organic compoundsare significantly higher for steel than for wood. The steel wall requires 25 times more water than the wood wall, primarily at the manufacturing stage, and steel manufacturing also has a greater impact on the quality of the waste water during manufacture. Inuse building materials have an impact on the environment, mainly because the choice of building materials will significantly affect the energy requirements for heating and cooling. Wood framing in a wall is a relatively good thermal insulator compared to steel framing, which is a good conductor of heat and acts as a thermal bridge. A steelframed 2 by 4 wall with R12 fiberglass bats has an overall Rvalue of only 6 to 6.85, while a wood 2 by 4 wall has an overall Rvalue of about 10.9.
Wood is the only building material derived from a renewable resource.
It is considered an agricultural crop that is harvested and replanted in a continually regenerating cycle while nonrenewable resources such as iron ore are mined on a permanently depleting basis. A 1976 study by the National Research Council committee on Renewable Resources concluded that producing 1 Ton of steel requires 50.3 million BTU oil equivalent, compared to 2.9 million BTU oil equivalent for 1 Ton of softwood lumber. A 1991 U.S. EPA listing of toxic substances released and transferred in the manufacturing process, indicated primary metals at 757 million pounds, fabricated metals at 103 million pounds, plastics at 195 million pounds, petroleum at 103 million pounds and wood at 38 million pounds. Trees are a renewable resource. Forest products are also recyclable and biodegradable.