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Green Basics

Steel Studs

Steel Studs Require Exterior Insulation to Avoid Thermal Bridging

Steel is easily recycled

Wood is much more common than metal when it comes to framing houses, but light-gauge steel studs outperform their wooden counterparts in a number of categories, such as recycled content, rot resistance, and reduced job-site waste. Steel framing has two major drawbacks, however: high cost and much lower energy performance.

Metal conducts heat

While there is much to be said in favor of steel framing, the key drawback is its poor thermal performance. Steel conducts heat much more effectively than wood, and even though the web is far thinner in cross section than 2x material, heat loss is significant. The California Energy Commission claims that a steel stud conducts 10 times as much heat as a wood 2x.

This thermal bridging drastically lowers the performance of insulation in wall cavities. A study by the Oak Ridge National Laboratory (ORNL) found that thermal bridging in a conventionally framed wood wall lowers the performance of cavity insulation by 10%; in a steel-frame wall, performance drops by up to 55%. Simply making wall cavities deeper to compensate for this thermal short circuiting is ineffective.

The ORNL research, however, looked at a number of possible solutions and found that steel-stud walls can perform as well as or better than similar wood-frame walls. The most common fix is to wrap the exterior of the building with rigid foam insulation, which provides a thermal break for the steel framing. A steel-framed wall wrapped with foam performs better than a steel-framed wall without foam — but a wood-framed wall wrapped with foam performs better still.

Other options cited in the ORNL report included using spacers to isolate the sheathing from the studs, and using foam-covered steel studs; both techniques interrupt heat conduction through the steel frame to the outdoors.

Perhaps the best fit for steel framing is…

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