64 RCI 0514

RCI May 2014

FLAT ROOFING & FLEX SYSTEMS Paul Barker, technical director at Triflex: “It would also appear that those asking questions believe that zero means zero, i.e. zero pitch means zero falls, or in the simplest terms, completely flat” At the recent Ecobuild exhibition at ExCel London, in addition to sustainability, green credentials and the environment generally, a large proportion of the questions dealt with by the Triflex team related to zero pitch or completely flat roofs, both exposed and inverted. Whether the questions came from architects, specifiers, surveyors or contractors, it appears that there are various different pre-conceptions towards the implications of completely flat construction. What is also clear by the level of interest by those designing, specifying or waterproofing these roofs is that there may be potential benefits – whether economic, green or construction programme related, or other – and on this basis the question is unlikely to go away. It would also appear that those asking questions believe that zero means zero, i.e. zero pitch 064 MAY 2014 RCIMAG.COM Falling to zero Paul Barker, technical director at Triflex, discusses the issue of exposed and zero pitch on completely flat roofs means zero falls, or in the simplest terms, completely flat. Issues with zero pitch Whether or not a roof is designed to be zero pitch, it is generally accepted that the majority of roofs will be subject to some standing / ponding water, particularly during or following heavy rainfall. There are a number of reasons why this may not be desirable, including: Waterproofing: There is a greater potential for water penetration if the waterproofing fails as a result of standing water / ponding, or is damaged / compromised in the area of the standing water / ponding. Structural: The weight of the water can create an increased load on the structure, leading to potential deflection, and ultimately could lead to structural issues. Safety: Water in any trafficked environment creates an increased risk of slips, trips and falls, particularly in the winter when the water can freeze. Standing water can also allow a build-up of algae and other matter which can make the surface more slippery. U-Values: Thermal performance may be affected by the presence of water, specifically in inverted build-ups. BS 6229:2003: This defines a roof as “having a pitch not greater than 10º to the horizontal”. For liquid waterproofing systems, BS 6229 states that the minimum finished falls at any point should be 1:80 for exposed waterproofing applications, yet goes on to state: “For certain specialist systems designed solely for buried applications, such as garden roofs, podia, and some car parks, specific reference should be made to the manufacturer’s Standing water on a flat roof: Issues surrounding standing water / ponding affect a wide range of the roofing industry, from architects and specifiers to surveyors and contractors


RCI May 2014
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