Minneapolis' Calhoun Isles' stately, rounded condominium towers are actually 50-year old grain elevators converted into homes through renovation and new construction. Cracks in the concrete were repaired; windows, doorways, floors, and balconies were added; and roofs were removed and two or three new floors added to the tops. Stairway towers were added at the far end of each cluster of silos, and a new 11-story townhouse building (with parking garage behind) was built connecting the two clusters.


Openings for 1200 windows, 300 patio doors, and 100 interior doorways were saw-cut in stages for the full length of the silos, from bottom to top (rather than making rectangular cutouts for each window and doorway), thus eliminating the need to drill core holes in order to start sawing. To support each wall section while sawing and to keep it from breaking out and falling, shore posts were wedged between the floor slab and the bottom of the wall section. To keep the panel from crumbling if there were several cold joints or cracks, a 6-inch channel was bolted to it vertically.


Composite steel and concrete floor systems were considered, but were found to increase slab thickness without reducing cost. The floor slabs within the silos were thus made of cast-in-place concrete, 8, 9, or 10 inches thick, depending on the diameter of the silo. Floor systems/circular balconies were anchored to the inside/outside walls by structural angles attached by bolts epoxied into drilled holes.


Two-inch-thick, foil-faced urethane insulation was fastened to the outside of the silo walls with Z-shape studs made of 20-gage galvanized metal. Metal lath was placed over the insulation and screwed onto the Z-shape studs, and a 3/4-inch thick coating of beige-colored Portland cement stucco was applied.