Q&A: Weight of Steel vs. Lumber Beams

A. When depth is not a restriction, it is almost always possible to design a steel I-beam that is lighter than the lightest structurally acceptable wood beam design, including glulams, LVL, and Parallam beams. And no matter how hard you try, solid timbers, built-up 2x beams, and flitch beams are almost always heavier than the lightest steel I-beam option — usually a lot heavier. Yes, it’s true that steel as a material is heavier than wood given two chunks of the same size. That’s because the density of steel is 12 times or so higher than the density of Southern Yellow Pine, for example. One cubic foot of steel weighs about 490 pounds, while the same size chunk of kiln-dried SYP wouldn’t top 40 pounds. But because the steel can be formed into very efficient shapes, like I beams, the overall weight of a steel beam is often lower than the lightest wood option.

In some cases, steel may be the only type of beam that will solve a problem. A good example is that common remodeling problem of removing a loadbearing wall without having the new support beam project below the ceiling. For long spans in a 2x10 floor, you can’t get enough stiffness from 9 1/4-inch LVLs or 9-inch glulams, but 8-inch steel I-beams come in a variety of widths and weights to handle almost any situation like this. In such a case, the framer may complain that the steel beam is very heavy, but it’s not heavier than the alternatives when there are none. There are also times when steel is ideal not because it can hold up a lot of weight, but because it can be welded into rigid frames. The modern two-story window wall leaves little room for plywood shear panels, but in high wind and seismic areas you can’t ignore the potential for racking that accompanies these lateral loads. A stiff moment frame of steel tubes or I-beams can often solve this problem when wood just won’t do the job.

—C.D.