One of the interesting things about the Steel Case House is that its available in several version. The logic here is that a steel house remains unusual, and as such difficult to get built. Either home builders have no experience in steel, or large commercial fabricators have no interest in doing a structure that is small like a house. By offering a range of configurations for the rest of the construction it makes it easier to find a combination that is workable with the trades you have easy access to. So the original uses a combination of masonry and wood frame to finish out. The SIPs version trades the masonry for insulated panels, better for cold climates. And the metal version trades carpentry for all steel trades, good if you have a light commercial builder to tackle the whole thing. And last the Timber Case version trades all steel for wood construction.