Do steel framing members have a place in green construction? On the plus side, they can be made with recycled material, a central tenet of sustainable building. But steel has high embodied energy and is a very effective conductor of heat—just think of the handle of a cast-iron frying pan that’s been on the stove for a while.
When steel framing is used to build exterior walls, all of the sheathing, windows, and door frames have to be fastened with screws. Inside, drywall is also attached to the framing with screws. Those thousands of fasteners increase thermal bridging that substantially circumvents insulation used in wall cavities and conducts heat in or out of the house depending on the season.
The Oak Ridge National Laboratory found that steel framing reduces the effectiveness of cavity insulation by 50% compared to its wood-framed counterpart. In 2-by-6 steel-framed construction, the cavity insulation of fiberglass batts nominally rated at R-19 provides an insulating value of only R-10. The only way around this is to attach a layer of rigid foam insulation to the outside of the building. Adding 2 inches of rigid foam insulation boosts the overall rating to R-20. But that’s about what you get with 2-by-6 wood framing on 24-inch centers. The only advantage is that the rigid foam insulation blocks a potential thermal bridge that also affects wood framing, though less dramatically. But this incremental improvement in performance adds substantially to the cost of the wall and the labor required to build it.
