One of the great innovations in US building technology was the nineteenth-century development of balloon framing for wood construction. It was, in simple terms, the substitution of a great deal of industrial infrastructure in the creation of wire nails and regularized lumber 2xs and 3xs for the carpentry skill required to make mortised joints. The eventual loss of wood joinery in building structure was a sad day for skilled craftsmanship, but balloon framing was the first step towards creating the huge number of new buildings that the westward expansion of the US needed.
The picture above, from a HABS survey of an 1860s hotel in Eureka, California, might be a little hard to read if you’re not familiar with the topic. Here’s a marked copy:
This is a photo taken from the outside with some of the clapboard removed. “A” marks the plank that makes up the exterior clapboard. “C” marks the similar plank that is the interior wall finish. “B” is the structural girt that supports the second-floor joists, which can be seen directly above it. If they all look the same, that’s more or less the point. A balloon-frame building is, in the modern phrase, a kit of parts.
In terms of structural engineering, the fact that the wall studs are continuous and two-stories high is meaningful. Plank sheathing is not a very good diaphragm material to allow the walls act as shear walls, and part of the balloon-framing idea was to get rid of diagonal braces and the more difficult joinery they represented. It difficult to make moment connections in wood, but using two story-studs gave the stud framing the ability to act as moment frames. Simple tension and compression horizontally where the second floor and roof meet the studs acts to create a couple that induces bending in the studs. It is extremely unlikely that people using this system in the mid-1800s were thinking in those terms, but trial and error would get them to this result.
A few years before that hotel was built, William Bell published The Art and Science of Carpentry Made Easy, a text that included a lengthy and clear description of balloon framing. He inadvertently showed a common problem with balloon-framed buildings while explaining how the system works. Here’s an illustration:
Figure 1 is an elevation of the side wall, showing the studs, the sill plate, the second-floor girt, and the second-floor joists. (Off-topic but interesting: there was no need for the bigger corner posts, but the system was still evolving and Bell didn’t realize that.) Figures 2 and 3 show the gable-end wall, with low-slope and high-slope roof variants. Those figures also show a serious problem: there’s no direct counter to the outward thrust from the roof rafters. I’ve seen buildings of this type where there was three or four inches of permanent outward bending of the studs between the second floor and the roof sill. Here’s a better version:
Again, figure 1 is the side wall elevation, figure 2 is the end wall. By making the second floor full-height, there’s room to put in attic joists, which serve to tie the gable roof and carry the roof thrust in tension. Making the building taller makes it stronger, which is a bit counter-intuitive in general, but particularly so for a scratch carpenter.
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