While the number of builders switching from wood to steel for house framing is relatively small, that number has been increasing steadily over the last few years all over the country, including in eastern North Carolina. Steel framing has a number of advantages over wood, but the research so far doesn’t support the idea that increased energy efficiency is one of them. In fact, most of the research suggests that steel framing has a substantial energy penalty attached to it.
Steel framing is attractive for several reasons. High on the list is the fact that steel is consistent and dependable. Since it doesn’t shrink or swell, the size will remain constant. It doesn’t warp, check, bow, or twist. As lumber from old-growth forests becomes more scarce and expensive, lumber from fast-growing, younger trees is increasingly what we find at the lumberyard. As the lumber quality goes down, using material that is dependably straight and true and dimensionally stable becomes more attractive to builders.
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Another feature of steel is that it is often made from recycled material and is recyclable at the end of the life of the building. From the standpoint of resource efficiency, taking a few old cars and making studs, joists, and rafters out of them, putting them into a building, and coming back fifty years later to re-use the pieces or melting them down to make washing machines or starships is certainly appealing.
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Other attractive features of steel framing include the fact that it doesn’t burn; it is inert (doesn’t give off terpenes which some wood species do and which some people are allergic to); and it is not attractive to insects.
So what’s the catch? The biggest problem is the energy issue. Steel is an excellent conductor of heat. It’s such a good conductor, in fact, that if you replace wood framing with steel framing it reduces the insulation value of the wall by as much as 40 to 50%. According to ASHRAE (the national Engineering Society), a 2x6 wall, with wood studs spaced every 24”, with R-19 insulation between the studs, has an R-value of R-16 (for studs and cavities, excluding sheathing, etc.) If you replace the wood with steel, the R-value goes down to R-8.6, a reduction of 46%. At this point, it should be clear that steel frames are giant heat suckers, pulling your heat out of the house in the winter and trying to heat the yard with it, and reversing in the summer, pulling heat into the house that you then have to cool with your air conditioner.
The final word, however, is not in, and more research is needed. It is clear, however, that one effective way to compensate for this thermal penalty is to use insulated sheathing on either the inside or outside of the steel frame. A minimum of 1” (R-5) seems to be needed, and possibly more. Other systems—such as one that has studs on 48” spacing and horizontal “hats” on both sides to which the drywall and sheathing are attached—may be effective, but adequate research hasn’t yet been done.
The bottom line? Cost is clearly a main issue. Lumber prices have been much more volatile than steel, and in some areas of North Carolina, steel has been competitive with wood at times over the last year or two. But be sure to compare all the costs, including the extra insulation needed to get the same performance, or you’ll pay the price in energy bills and comfort for as long as you’re in the house.
Article courtesy of Advanced Energy.
For more information visit www.advancedenergy.org |
