Today’s dive into Architectural Terra Cotta: Standard Construction is, on the surface, much simpler than yesterday’s. The plate has six ways to use terra cotta for a decorative door or window head. But, in my opinion, a closer look shows there’s multiple levels of fakery here, all in the good cause of presenting an aesthetically-pleasing masonry opening that could be easily built.
First, it’s important to note that all of these masonry openings are four feet wide or narrower. Four feet is the magic number for these details, because, since the early twentieth century, it’s been the size opening that was considered to be small enough for arching action to work. That means that the masonry won’t collapse if a lintel fails, which means that the lintels don’t need to be fire-proofed. These details, in 1914 or in the present, would look very different for five-foot openings.
The first four options have flat heads to the masonry opening, which is certainly simpler and cheaper for installing a door or window than the arches of the other two options. The flat versions all have steel-angle lintels, visible in the wall sections, while the arches do not. That doesn’t necessarily make a lot of sense. You can certainly span four feet with a flat arch, and building a flat-arch for the back-up brick in option A would not be any more difficult than building the segmental arch for the-up back shown in option E. Also, option C is something of a mystery, as the lintels do not support the terra cotta, but the terra cotta blocks are not properly shaped to develop much, if any, arching action. Note that the terra cotta arches in the veneer wythe of options E and F are not really terra cotta arches: there is solid brick fill within the terra cotta, providing a direct load path for compression.
All of these details show ties for the terra cotta: in all but option C, the ties are dashed-line Zs at the top of the terra cotta, intended to make sure the veneer did not move out of the brick plane. In option C, the ties are lower, behind the middle of the terra cotta height. There pretty much have to be similar ties supporting the soffit tiles below the steel lintels, but they’re not shown. Interestingly, those soffit tiles are the place these details deviate the furthest from reality: they were used, sometimes, at first, but over time it became clear that no one really cared if the bottoms of loose steel lintels were exposed.
