Design features and best practice in podium deck waterproofing : Examples and perspectives from UK industry

Podium decks — a basement roof at, or around, ground level which is not covered by superstructure — are an increasingly common feature in the modern built environment. This increase may be partly attributed to growing awareness of the need for sustainability. Green roofs, sustainable urban drainage, water attenuation and even parks and farms are being located on top of podium decks. Waterproofing of these podium decks is vital in order to use the space created beneath and also to prolong the life expectancy of the structure. This research analyses the available best practice guidance and then compares the key waterproofing design features with opinions from industry. Opinions are gathered first through 78 questionnaire respondents and then interviews with four experienced respondents with unusual views. These findings are then compared with case studies of podium decks with waterproofing failures. This research suggests that robust podium deck waterproofing design comes from the following choices in the fundamental features of waterproofing design for podium decks: a) reinforced concrete structural deck; b) fully bonded waterproofing membrane; c) waterproofing laid to a gradient to falls; and d) provision of a drainage void over the waterproofing layer. As a result of these findings, this paper calls for more authoritative best practice guidance on podium deck waterproofing design in a bid to reduce pressures in procurement that lead to weaker waterproofing design choices. This research may be of interest to built environment professionals because it identifies some fundamental features of podium deck waterproofing design and clarifies which design choices are perceived to deliver more robust waterproofing than others.