Historic Structural Detail: Vaulting Upwards

by Don Friedman on February 8, 2016

I’ve mentioned the circa-1900 use of Guastavino vaulting to provide steel-free solutions to common structural problems. To repeat my early comment, even though we think of thin-shell masonry vault as a large-structure technique, it was used in various niches as an ordinary structural form. My favorite Guastavino structures are right-angle and switch-back stairs, where the vaulting creates beautiful sculptural shapes as it turns to follow the stair path. But even in straight stairs, Gaustavino vaults are fascinating:

351 Riverside Drive - guastavino vault - original plans

That’s an original construction detail for the entry stair to a house. (As always, click to enlarge.) The dark-orange rectangles are brick walls with arches in them to provide access; the dark-orange curves are called out as “3 course Guastavino”. The curves are drawn with variable radii, but a single radius is given for each, suggesting that this section is more diagrammatic than prescriptive. The tile vaults support unreinforced concrete fill, which is the base for the single-piece stone treads that are the usable stair. The common method of building this type of stair over a cellar space was to use a couple of sloped steel beams with steel plates or angles on top to provide direct support for the tread stones. Over the long run those steel stair supports tend to rust and have to be replaced, while the all-masonry solution still looks great after 110 years:

351 Riverside Drive - guastavino vault - DSCN2395

In this photo, we’re standing under the larger vault (the gray tiles are visible at the top of the picture) looking through the arched opening in the intermediate wall to the smaller fault (the red and brown tiles are visible through the arch).

The advantages of this system are pretty simple: the use of inexpensive materials, a relatively small need (compared to other materials) for falsework and temporary supports during construction, and very good long-term resilience when exposed to water. The system was gradually abandoned in favor of reinforced concrete, but r/c has only the advantages of being easier to analyze and being more familiar. Reinforced concrete might have better seismic performance for large structures – although I do not know that to be true – but that is unlikely to be true at this domestic scale. On an equal playing field, Guastavino is superior, but that is ultimately a meaningless statement: construction technology cannot be examined in a vacuum but must be taken in the context of the available trained labor force, the governing codes, and the ability of designers to work with the system. It took a few decades for concrete to displace tile vaults and it would probably take as long for us to attempt the reverse movement, if that is even possible.

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