The Steal in Steel
Since the day in March of 1862 when the ironclads Monitor and Merrimac dueled to a draw at the Civil War Battle of Hampton Roads, iron—and its derivative steel—have not only revolutionized warfare, they have been the backbone of the industrial revolution that was to begin in earnest following the end of the Civil War. As well, due to its excellent tensile strength, steel has changed the way we build the built environment, from roads to bridges to skyscrapers.
Steel has long been the material of choice for the modern construction industry, from the time the first skyscrapers rose from the ashes of the great Chicago fire of 1871 till today. For the world’s first suspension bridge the Brooklyn Bridge (1883), spanning the East River between Lower Manhattan and Brooklyn, steel made it possible. Having the highest strength-to-weight ratio of any building material, steel is lightweight as compared to other building materials such as masonry or concrete. Steel provides an easy-to-use, durable, versatile and cost-effective means by which structures can be quickly and efficiently built. Best yet, it has long been recycled and is an entirely recyclable material. For more than 150 years, iron and steel have been recycled. In North America alone, there are approximately 12,000 auto dismantlers and 1,500 scrap processors—many of which have been in business since the 19th Century.
The steel industry itself has long been committed to recycling and environmental conservation for both economic and altruistic reasons. The Steel Recycling Institute is an industry sponsored organization dedicated to promoting and sustaining steel recycling (www.recycle-steel.org). Since 1970, when the first Earth Day was instituted, the steel industry as a whole has spent more than $7 billion for equipment specifically designed for the control of air, water and solid waste pollution. Annually, the industry averages about $500 million on capitol spending toward environmental concerns, and about $3 billion on new processes and technology. This commitment to recycling results in the use of less raw materials and reduced energy consumption. The electrical energy required to power approximately 18 million homes is saved annually; about a 75-percent reduction in energy consumption has been realized by the industry. Alone, 1 ton of recycled steel saves in raw material terms:
• 2,500 pounds of iron ore
• 1,400 pounds of coal
• 120 pounds of limestone
Return to senderSteel remains the most recycled material in the world. More steel is recycled than paper, aluminum, glass and plastic combined. The embodied energy of a building material is considered in many environmental impact rating systems. That is, the energy required to produce a finish product. Due to the modern steel industry’s advances in processes and technology, the EE in contemporary steel production has been greatly reduced. By recycling, the EE is amortized via the inherent recyclability of steel into future steel products. All steel products contain recycled content and are wholly recyclable.
A comparison of steel to wood building products reveals a significant differential in the level of eco-disruption—a benchmark for environmentally conscious construction. Based on a comparison of an equal number of homes built, and on sustainable 70-year wood harvests, the life-cycle assessment for eco-disruption of steel is less than 1 percent for that of wood.
In 1999, 67 million tons of steel were recycled in the U.S. Since recycling steel is more cost effective than mining virgin ore, recycling has duel benefits for the industry’s bottom line and the environment. Out of every 3 pounds of new steel produced, 2 pounds are derived from recycled steel. However, the long life cycle of steel requires the industry to maintain ongoing mining operations for virgin ore.
Steel used in the construction industry is produced by what is known as the electric arc furnace method. Rather than the basic oxygen furnace method, whereby drawability is the most desirable characteristic (eg. cans, pails, drums, etc.), the EAF method is used whereby strength is most desirable. The EAF method allows for use of 100 percent recycled steel to make new steel such as structural beams, columns, steel plates, re-bar, etc. Though dimensional lumber (aka “stick-built”) has long been the method of choice for homebuilding in North America, light-gauge metal framing is gaining favor with many homebuilders. However, for now and the foreseeable future, wood will remain an essential material for home construction.
From an environmental perspective, light-gauge metal framing has several advantages over wood framing. Since steel has a greater strength-to-weight ratio, fewer framing components are required for a light-gauge metal framing house as compared to a stick-built wood-frame house. As well, since 90 percent of North America’s old-growth forests have been harvested, the cost for wood, in general, has increased while overall quality and availability has decreased. Light-gauge metal framing has long been used as the standard for commercial and residential interior wall assemblies—both rated and non-rated—it remains an important component of the walls and ceilings industry. Unlike wood, which is subject to warping, splitting, bowing, deflection, settling and creeping, light-gauge metal framing suffers not from these maladies. It is dimensionally stable, non-flammable (cannot support combustion), infestation/rot proof and cannot suffer—as wood can—from organic degradation.
The inherent strength and stability of light-gauge metal framing reduces HVAC energy usage by reducing significantly air infiltration around window and door openings by better maintaining the building envelope. Advances in the technology of light-gauge metal framing such as new joist/truss floor systems and load-bearing wall assemblies have seen light-gauge metal framing’s usage in residential construction increase significantly. New thermal light-gauge metal studs provide superior exterior clear wall thermal performance.
Waste not, want notLight-gauge metal framing provides a cost-effective alternative to traditional wood framing as well. Since light-gauge metal framing can be ordered or purchased to specified lengths, rather than be limited to standard stock lengths, scrap and debris on-site are minimized. The processes and quality control in the manufacture of light-gauge metal framing eliminate the need to cull-out unacceptable material as is required for dimensional lumber since light-gauge metal framing cannot split, twist or otherwise warp as can dimensional lumber.
Light-gauge metal framing has a great advantage too in that it can be panelized for pre-fabricated floor and ceiling, wall and roof assemblies, on or off site. Such panelization often makes the installation process much more efficient and cost-effective. Where the elements of nature are concerned, light-gauge metal framing again proves its worth. In high-humidity conditions it does not shrink or swell over time as does wood. This provides for better aesthetic interior and exterior appearances and finishes. For seismic restraint and wind loads, again, it outperforms traditional stick-built wood-framed construction.
Consider a 2,000-square-foot house framed with light-gauge metal. By generating only about 1 cubic yard of recyclable scrap metal, costly carting, disposal and tipping fees at local landfills are minimized and completely eliminated. The same 2,000-square-foot house stick-built with dimensional lumber requires between 40 to 50 trees (about one acre) to be harvested. The steel required for the light-gauge metal framing version of this house would require only about six scrapped cars. Consider too that, upon the completion of the light-gauge metal framing houses’ life cycle, 100 percent of the light-gauge metal framing contained therein is recyclable. Steel scrap is commonly collected from construction and demolition sites. Upon demolition of the wood-framed house, most of the framing members would end up in a landfill.
Considering the total life-cycle energy consumed by the 2,000-square-foot light-gauge metal framing house—inclusive of all heating, cooling, refrigeration and lighting—only 6.25 percent is required for the energy that was originally required to produce the steel for the light-gauge framing components. Reason being that at a minimum, 25 percent of the steel for the light-gauge metal framing was from recycled steel, but it could be as high as 100 percent recycled source for the raw material. W&C