The price of framing lumber is notoriously volatile. At the time of publication, wood prices were at record highs, and building owners and contractors continue to look for alternatives to wood framing for their projects.
A recent Steel Framing Industry Association (SFIA) comparative cost study of the framing of a 5-story, 49,900 SF, mixed-use apartment building showed that CFS framing costs only 0.92% more than light wood framing. If the same structure had been built reflecting today’s lumber prices, the cold-formed steel framing package would cost 24% less than the wood option, according to an R.A. Smith bulletin.
Steel’s relatively low cost and its proven track record of providing sustainable benefits have increased the number of building professionals evaluating the use of CFS and structural steel as alternative framing materials. Thus, some designers and contractors may be using steel framing for the first time.
How do cold-formed steel and structural steel compare?
CFS and structural steel share some performance characteristics — durability, strength, affordability, ease of maintenance and sustainability.
However, let’s discuss some important differences between these two material types.
Cold-Formed Steel Framing
Cold-formed steel, also called light-gauge steel or metal stud framing, is made from structural quality sheet steel formed into C-sections and other shapes usually by rollforming the steel through a series of dies. No heat is required to form the shapes (unlike hot-rolled steel), hence the name cold-formed steel.
CFS is typically referred to as light-framed construction. The vertical and horizontal structural elements are primarily formed by a system of repetitive framing members. The framing members are typically spaced at 16 or 24 inches on center, the spacing variations depending upon the loads and coverings.
- Preferred for commercial projects: CFS is the preferred material for curtain walls and partitions in multifamily and commercial construction due to its lightweight, high strength, ease of installation and non-combustible nature.
- Flexible use: CFS delivers many advantages in the construction of wall panels, floor joists, roof trusses, and structural walls.
- Little cutting: CFS framing is similar to wood. But, CFS is manufactured to precise lengths, so very little cutting and sizing occurs at the job site.
- Reduced waste: CFS framing produces far less on-site waste than wood framing, making debris removal less costly.
A variety of CFSteel thicknesses are available to meet a wide range of structural and non-structural applications (range from 0.0147 inches to about 1/8 inch). Standard CFS products are defined in AISI S201, North American Standard for Cold-Formed Steel Framing – Product Data, 2012 Edition.
CFS is increasingly being used as the primary structural system for buildings 10+ stories. It is also gaining use in the framing of single-family homes. A variety of CFS framing products are available from various manufacturers.
Structural Steel Framing
Structural steel is hot-rolled, much thicker, and considerably stronger and heavier than CFS. “Hot-rolled” means the member is shaped while the steel is molten hot. Because it is thicker and much heavier than CFS, hot-rolled steel fastening methods employ welding, bolting and riveting.
The American Institute of Steel Construction notes the following benefits of structural steel:
- No height limitation: There is no limit on building height due to structural steel’s load-carrying capacity. Many of the tallest buildings in the world use structural steel framing.
- Flexibility in space planning: Structural steel allows for long spans and open, column-free spaces, and is not dependent on load-bearing wall construction. Increased usable floor space and flexibility in space planning are major advantages and allow for greater design opportunities.
- Reduced waste and pollution: On average, structural steel produced in the U.S. is composed of 93% recycled content, and 100% of a structural steel frame can be recycled into new steel products. Steel’s high strength-to-weight ratio coupled with a low carbon footprint — 1.16 tons of CO2 per ton of fabricated hot-rolled steel — results in an overall reduction of the embodied carbon of a typical structure.
Column spacing is typically 25 to 45 feet on center, with spacing variations lower and higher depending on architectural requirements. The range of available shapes and sizes allows virtually any architectural requirement to be met.
Hot-rolled structural steel shapes such as wide-flange beams and columns are defined in ASTM A6, Standard Specification for General Requirements for Rolled Structural Steel Bars, Plates, Shapes and Sheet Piling. A variety of hollow structural sections (HSS) formed from steel plate are available from various manufacturers. Built up structural sections can be fabricated using steel plate.
Structural steel framing is typically designed, fabricated and erected in accordance with standards developed by the American Institute of Steel Construction in the United States and the Canadian Standards Association in Canada. It is also adaptable to almost any architectural layout and is used routinely on a variety of building projects.
Structural steel is the most popular framing material for non-residential buildings in the United States, with over half of the constructed square footage framed in structural steel on an annual basis.
Comparing CFS with Structural Steel Framing
The weight of CFS compared with structural steel typically plays a part in the type of steel framing used.
For a small-scale building, the weight can add cost to the project. For single-family homes, structural steel is typically not needed to frame the entire structure. But for large commercial buildings, the strength of structural steel may be required.
- The ground floor podium may be framed with structural steel to accommodate the large open areas that are on the ground floor for amenity space.
- The unit floors above may be framed with CFS and make up the remaining floors on the buildings tower.
Both CFS and structural steel steel provide excellent framing options for low, mid and high-rise buildings. Strong, durable, recyclable and cost-effective, steel framing is the material of choice for building owners and designers.