Publication Date:
Wed, 2000-01-26 18:00
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Summary
| The framing members are C-sections with standard dimensions similar to wood framing members in stick-framed construction. Manufacturers promote steel framing as a cost effective, superior alternative to wood framing. |
Details
Steel mills produce sheet steel, the base material for steel framing. Sheet steel is roll-formed into the shapes used for framing and is protected from corrosion with zinc galvanization. Although there are a variety of shapes available, the primary shapes used in residential construction are the C-shape stud and the U-shaped track.(*see Figure). Framing members are produced in thickness' from 18 mils (a mil is 1/1000 of an inch) to 97 mils.
Steel framing members are produced to strict standards of strength, consistency, and dimensional stability. Steel framing provides excellent design flexibility due to the inherent strength of steel, which allows it to span increased distances and it can be designed to withstand high wind and seismic loads and is non-combustible
Installation
Stick-built or conventional steel framing is typically a one-for-one replacement of wood framing members for both non-load-bearing and load-bearing applications. The steel studs, joists and rafters fit into a top and bottom track. Steel framing members can be cut with a chop saw, aviation snips or electric shears . The primary fastener used in steel framing is the self-drilling screw which can be labor intensive when compared to the phenumatic framing nailers used in wood framing. However, there are new fastening systems that utilize crimping, welding, and pneumatic nailers that promise to speed up the construction process. Typically, the top track is not capable of transferring vertical loads. Studs, joists and rafters must be aligned vertically to transfer vertical loads . This framing technique is called in-line framing .
Benefits/Costs
Steel framing contains up to 28%-recycled material and construction waste generated during framing is 100% recyclable. It is resistant to corrosion, warping, and termites. Framing members can be ordered cut-to-length which can result in reduced on site labor costs and reduced on site waste. Framing weighs up to two-thirds less than conventional materials. Lightweight steel framing lends itself to panelization techniques that can speed the on site construction process by allowing the assembly of walls in controlled environments. Figure ** shows panelized steel framed walls loaded on a trailer ready for transportation to the job site. Steel framing members also have pre-punched holes that allow for easy installation of electrical wiring and plumbing.
There is an ample supply of steel, which results in stable prices. In many areas, it is cost effective compared to wood framing. The cost effectiveness of steel framing greatly depends on the prevailing price of wood framing materials. It is commonly accepted that when the framing lumber composite price exceeds $400-$450 per thousand board feet, steel is less expensive than wood framing.
Limitations
Steel framing members conduct heat/cold which results in a process called thermal bridging that can lower the effectiveness of cavity insulation and cause streaking (ghosting) on the interior finish of walls and ceilings. Exterior insulating sheathing should be installed in cold climates to mitigate thermal bridging and ghosting problems. Even though conventional steel framing is very similar to wood framing, there is a significant learning curve that must be completed before any cost savings associated with the use of steel can be realized. In-line framing requires careful layout of studs, joists and rafters to ensure that they align vertically. There is also a shortage of framing crews trained in the installation of steel.
Code/Regulatory
Steel framing is recognized by all major building codes. Recently, a set of prescriptive methods for residential steel framing was adopted by Council of American Building Officials (CABO), and are now included in the CABO One and Two Family Dwelling Code. The prescriptive methods contain tables for stud sizing and spacing, joist and rafter spans, fastener schedules and construction details. In areas that recognize CABO, the prescriptive methods will allow the construction of stick framed steel homes without the certification of a professional engineer. In areas that do not yet recognize CABO, a professional engineer must certify the plans.
Availability
There are many manufacturers throughout the country. These manufacturers typically have a network of distributors who sell the members directly to builders. Also the number of building suppliers that stock steel framing is increasing. Even with the increasing availability, it is typically not as readily available as wood framing material.
Contact(s)
Do you have a specific question about this technology and/or its 'real life' applications? Try the contacts listed below:
American Iron and Steel Institute
1101 17th Street, Northwest
Suite 1300
Washington, DC, 20036
http://www.steel.org [1]
Light Gauge Steel Engineers Association
2017 Galbraith Drive
Nashville, TN, 37215
615/386-7139
NAHB Research Center, Inc.
400 Prince George's Blvd.
Upper Marlboro, MD 20774
HomeBase Hotline
800/898-2842
