Paving Systems Over Plaza Waterproofing Membranes: The Importance of Membrane-Level Drainage

March 30, 2009
Publication: RCI Interface

Abstract: Subsurface drainage in any paving sys­tem is critical to its long-term performance, particularly in freeze-thaw climates. "Paving" is a broad term that includes both continuous (i.e., asphalt or Portland cement concrete) and unit paving systems (i.e., brick, stone, or precast concrete pavers, installed either in an open-joint configura­tion or with filled joints). While each of these systems performs differently, they all allow some water to seep through cracks or joints. Where the paving is installed on grade, this incidental water typically seeps down into the ground, aided by gravel lay­ers and/or perforated pipes where appro­priate. However, when paving is installed over a waterproofing membrane, moisture that pene­trates it can become trapped in the paving and cause drainage and durability problems. Paving installed over waterproofing membranes can be found on pedestrian or vehicular plaza decks over below-grade parking garages or occupied space, and also on rooftop terraces and bridge decks. These applications require membrane-level drainage (see Figures 1A and 1B). Designers mus make provisions for water that infiltrates the paving and collects on the mem­brane to travel laterally to a drainage outlet.|Plaza drainage systems such as paverpedestals, prefabricated drainage compos­ites, and bilevel drain fixtures have long been available, but we continue to see fail­ures in paving systems over waterproofing where membrane-level drainage was not provided. This article presents examples of problems the authors have observed on existing plaza decks, and it reviews princi­ples for designing successful membrane-level drainage in new or remedial designs to prevent premature deterioration of the paving.

Keywords: Plaza Waterproofing