Steel, the most commonly used metal in building products today, has long been a staple in commercial construction. Recently, however, it has begun to make strong inroads into the residential building market.
According to the National Association of Home Builders, shipment of light gauge steel for residential, site-built housing grew by nearly 44 percent in 1998. The amount of steel used for framing single-family homes grew by more than 52 percent; the use of steel floor joists increased by 25 percent.
The move to steel in home construction was fueled by rapidly increasing lumber prices and a need to conserve timber products. Builders are discovering other reasons, however, to use lightweight steel studs, joists and beams.
Steel homes use nearly the same framing techniques employed in wood-framed buildings, and construction costs run about the same. Unlike wood, however, steel is impervious to termites. It provides added resistance to fire and earthquake. Steel ceiling joists can span greater distances than wooden ones, allowing new design possibilities for architects and builders.
One word of caution: building a home with steel can be less energy efficient than building with wood, so extra care needs to be taken to insulate. Because metal transfers heat and cold much more readily than wood - 400 times more readily - steel studs can create "thermal bridges" to the outside of the house. To stop this transfer of heat, contractors should wrap steel framing with insulating board (or rigid insulation) in addition to placing conventional batts of insulation between the studs.
Steel is also highly recyclable, and many dealers buy used steel as scrap. Nearly 70 million tons were recycled in 1998 - from cans to cars, from appliances to steel girders in skyscrapers and bridges. Steel is America's most recycled product, with an overall recycling rate of 63.8 percent.
Steelmaking is an energy-intensive industry that begins with mining iron ore, smelting it, transporting it, melting it down with other alloys and finally milling it so it can be turned into finished products. Reusing old steel not only saves energy and natural resources, it lowers the total cost of producing new steel.
Steel mills use one of two types of furnaces to make new steel. Both furnaces recycle old steel products into new steel, but each is used to create different products for varied applications.
- The first, the basic oxygen furnace, uses a minimum of 25 percent steel scrap to make new steel. This furnace produces the steel used in flat-rolled steel products, like cans, appliances, automobiles and steel framing.
- The other type of steelmaking furnace, the electric arc furnace, melts virtually 100 percent steel scrap to make new steel. This steel is used primarily to make products that are long shapes, like steel plate, rebar and structural beams.
The Steel Recycling Institute says recycling saves enough energy annually to electrically power 18 million homes for the year. Reusing a ton of steel - the amount in the average car - saves 2,500 pounds of iron ore, 1,400 pounds of coal and 120 pounds of limestone.
People concerned about using natural resources wisely can purchase salvaged steel from scrap dealers, and new steel with a verified recycled content of 30 percent or greater is now available in the United States. These sources of steel may be appropriate for some nonstructural construction uses.
Health Problems with Steel
Indoor air pollution is not a problem with steel. The only exceptions are when exposed metal requires polishing, cleaning, or repainting; fortunately, this can be done with low-toxic or non-toxic products.
On rare occasions, homes in which thermal bridges remain intact can have problems with mold, especially in colder climates. In the worst case scenario, moisture condenses on the cold areas of the wallboard directly over uninsulated steel studs. On the interior walls, these cold spots develop into darker areas called "ghost marks" where dust and mold accumulate along the colder, damp stud lines. Adding insulation to the outside of the home usually solves this problem.