The island home is entirely concrete: the floors, interior and exterior walls, and roof. The cantilever from the pier toward the left of this photo to the tip of the house over the water is 28 feet, believed to be the longest one Wright ever designed.
The island home is entirely concrete: the floors, interior and exterior walls, and roof. The cantilever from the pier toward the left of this photo to the tip of the house over the water is 28 feet, believed to be the longest one Wright ever designed.

Designed in 1950 for a specific site (a rock out-cropping passes right through the home) on an island in Lake Mahopac near Carmel, N.Y., this home is approaching completion. The structurally reinforced concrete design remains faithful to Wright's original plans, but improvements in concrete technology over the past 55 years are evident.

Building a concrete home on an island creates significant challenges. First, materials to make 950 cubic yards of concrete had to be moved over the ice in winter and by boat in summer. No large equipment could be safely moved to the site, so all the concrete was batched in small drum mixers with care taken to maintain a high level of quality control—strengths averaged 8000 to 9000 psi.

Two design features in the home represent concrete construction at its very best. A pier in the center of the 45-foot-long living room has a fireplace built into it. This pier supports a 28-foot cantilevered slab that extends over the lake with an outdoor 260-degree view. The pier also supports two unequal transfer beams that hold the ends of two unsupported 45-foot-long concrete ceiling beams, which in turn support the 6-inch-thick concrete roof over the living room. This is all made possible by post-tensioned reinforcement placed in the cantilevered slab, the transfer beams, the ceiling beams, and the roof deck.

The other feature that uses concrete to its best advantage is a 26-foot-diameter horizontal skylight in the front entry. The supports for the glass, which cross through the area making pie shaped window lights, are ornately formed, post-tensioned concrete beams that also secure the glass. Cabinetmakers used cabinetgrade plywood to build the intricate formwork. The contractor, Lidia Wusatowska-Leighton, took great pains with this centerpiece.

The home has 5000 square feet of living space. All the cast-in-place forms were built onsite because of the unusual shapes and angles. Some walls were shot-creted using the Tridipanel panel system—a 4½-inch-thick center sandwich of expanded polystyrene insulation with 2-inch-square galvanized mesh mounted on either side.