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Designing Plaza Hardscapes Considerations from insulation and waterproofing to structural support by Kurt R. Hoigard, PE, SECB, FASTM, and Brian T. Lammert, SE, PE, CDT All images courtesy Raths, Raths & Johnson OUTDOOR PLAZAS PROVIDE OPEN SPACES THAT BREAK UP THE MASSING OF NEIGHBORING BUILDINGS AND PROVIDE A RESPITE FROM BUSY SCHEDULES. IN URBAN ENVIRONMENTS, THEY ARE FREQUENTLY CONSTRUCTED OVER UNDERLYING OCCUPIED SPACES USED FOR PARKING, STORAGE, CONFERENCE ROOMS, AND CLASSROOMS. LANDSCAPE TREATMENTS TYPICALLY INCLUDE PLANTERS, TREES, AND PAVING OF VARIOUS TYPES FOR PEDESTRIAN AND/OR VEHICULAR TRAFFIC. THE RESULTING CONSTRUCTION IS A COMPLEX SANDWICH OF MATERIALS RANGING FROM THE LANDSCAPE AND HARDSCAPE COMPONENTS VISIBLE AT THE SURFACE TO THE STRUCTURAL ELEMENTS KEEPING THE PLAZA FROM FALLING INTO THE OCCUPIED SPACE BELOW. The materials and components used in plaza construction over occupied space must provide thermal resistance, water management, structural capacity, a durable wearing surface, and an attractive finished appearance. Designers select product characteristics to fulfill these functions, typically relying on technical data and recommendations from product manufacturers. The authors have found the available published manufacturer technical data is inadequate for designing plazas to which heavy loads will be applied. When not properly accounted for in the plaza design, the interaction of the various materials and components can result in unplanned movement and damage to the exposed hardscape materials. Plaza damage that has been investigated by the authors attributed to hardscape/substrate stiffness interaction include concrete topping slab cracking, paver cracking, paver edge raveling, and paver joint deterioration. 46 the construction specifier | april 2014 CS_April_2014.indd 46 3/18/2014 3:07 PM