In the space of two days, I got two emails from people asking the exact same question. So here’s clarification, which I’ll have to include in the next printing! Thanks to those who wrote...
“Typical dome height” is 16” (p. 51). Some pizza ovens are lower because they’re used exclusively for pizza, which means they can have a low door without losing the 63% ratio of dome to door height — and they don’t have to worry about getting a turkey through the door.
The previous edition didn’t specify an ideal height, and in fact, a high domed oven will work — the traditional southwestern horno is typically quite high. In general, however, for bread ovens you don’t want to increase oven volume any more than you have to, as it reduces the concentration of steam — and steam is what causes the formation of an ideal crust. In addition, your door would have to get higher and higher in order to maintain the 63% ratio.
If you make a really large oven, it gets much trickier maintaining the right curvature of the dome to keep it from falling in (“large” might be 10 feet wide or more...). But otherwise, I use 16” as a standard height for 22”, 27”, 36”, and larger ovens. The largest I’ve built was 4 feet across, with a 16” dome.
At that size, I was very careful to make sure that the shape of the dome was truly catenary. In fact, I made a template by hanging a loop of heavy cord so that the ends were 48” apart, and the center hung down 16”. I traced the line, cut it out, and used the template to shape the sand form so that I would be sure of the strength of the dome.
The little pic is a postcard of a typical Southwestern horno — clearly more than 16” high inside the dome.