Mushroom System

In September 1914, the New Orleans architectural firm of Toledano, Wogan and Bernard was completing a new skyscraper in the Central Business District, the Johns-Manville Building (441 Gravier Street/225 Magazine Street).  The building employed a recently patented flat-slab construction system that allowed for thinner slabs, broader spans, and reduced shear. Minneapolis-based engineer Claude Allen Porter (C.A.P.) Turner (1869-1955) developed the system  after years working as a railroad bridge engineer for the Soo Line.

Turner's first documented mushroom system building was the Johnson-Bovey in Minneapolis (1906; razed). Milwaukee's Hoffman building (now Marshall) was completed the following year.(1)

In New Orleans, there was considerable interest in the Turner Mushroom System. J.T. Mann & Company was Turner's southern agent, and envisioned the Johns-Manville building its prototype.  The locally-published Building Review reported to the Louisiana Chapter of the American Institute of Architects:

"The building is the highest of its kind in this city and is of the Turner Mushroom system construction. It is fireproof, has a modern sprinkling system, extensive fire extinguishing devices and automatic door shutters. The walls of the building are stuccoed, trimmed with press brick and polychromatic terra cotta, models of which were colored in the architect's office, giving a general color scheme that presents a composition of refinement and good taste. The average test of the floors have proven a loading capacity of 600 pounds to the square foot in spans averaging 20x20 feet with a deflection of not more and in some cases much less than 1-8 of an inch."

(1) In 2002, the American Society of Civil Engineers declared it a National Historic Civil Engineering Landmark.

(2) "A New Turner Mushroom System Building." Building Review (19 September 1914), p. 8.

Images above: C.A.P. Turner, consulting engineer. Column Top Detail, Johns-Mansville Bldg., New Orleans, LA. Blueprint.  Toledano, Wogan & Bernard Office Records; "Testing Floor Load in the New Johns-Manville Mushroom System Building." Photographic reproduction. Building Review (19 September 1914), p. 8. Both Southeastern Architectural Archive, Special Collections Division, Tulane University Libraries.