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FALLS IN FLOOR FINISHESIn this article Colin Cass looks at issues related to falls in floors, and changes to the Australian Standardsoninternal and externalwaterproofingand the BCA.Fall, slope or gradient, whatever you call it, how much is enough to effectively remove waste water from a floor?There appears no simple answer to this simple question. The water removal needs of a shower floor are different to those of a toilet floor, and different again from an exterior balcony. The type of tile also affectsthe “run off” of water. Too much fall doesn’t look good, and a slip hazard can be created, too little, and water may stay in puddles.Traditionally tilers tended to incorporate more than the minimum required, as problems seldom come from too much fall, complaints definitely come from too little. Low amounts of fall put increased pressure on tilers to be accurate in screeding the bedding mortar, as even a slight deviation from plane could leave a hollow that would hold water, and this is couldbe regarded as adefect.But tile sizes are getting bigger and bigger, and particularly with tileslarger than 300mm x 300mm, tilers encountered problems of incorporating reasonable falls and avoiding tiles lipping as their large flat surfaces didn’t fit the “dish” to thefloorwaste.Large tiles in shower recesses can belaid with crossways or transverse cuts radiating from the waste so lipping was minimised, however, these transverse cuts were often considered ugly, so lessfall is oftenincorporated toavoid these cuts. The increase in use of polished porcelain tiles and polished natural stone has also seen a change in the surface tension of the tile finish. How can one expect all the water to flow to the drain, when the surface causes beading by its very nature. No amount of slope would see all the water run off. Think of the angle of a car windscreen, water still beads there, in fact it beads on vertical window glass, so complete and immediate run off is unrealistic.How is fall measured?While itis sometimes referred to in “degrees” and sometimes as a certain measurement over a certain distance, most construction specifiers stipulate it as a ratio. For example 1:100 means for every 100 units along a floor, the floor should fall by 1 unit, 1:60 is steeper as the floor would fall 1 unit in only 60 units, and a 1:1 ratio would be a 45° angle. [1:100 is 10mm per lm, while 1:60 is 16.6mm per lm and 1:50 is 20mm per lm.]What do the Codes say?
The codes related to tiling and waterproofing are very vague when it comes to prescribing an amount of fall. Until 2007 AS 3958.1 “A guide to the installation of ceramic tiles” referredonly obliquely to falls in statements like “where possible, falls in the floor should be formed in the base concrete so that anapplied screed is of uniform thickness.”, or “slope, where essential, should be in the sub-floor” Ratios are never mentioned.AS 3958.21992“A guide to the selection of a ceramic tiling system”, in clause 4.4.6.2 states, in an equally non committal manner;“FALLS: Where it is necessary for the finished floor surface to be provided with falls to drainage outlets and the like, where possible these falls should be constructed in the supporting structure.” These standards are guides, but AS 3740 “Waterproofing of wet areas within residential buildings” is a “deemed to comply” standard, and it is called up as a method of meeting the “performance requirements” of the Building Code of Australia (BCA). This standard calls for falls in showers to be between 1:60 and 1:80and not less than 1:100 in areas outside the shower in its appendix B, and the BCA 2008 reproduces the appendix almost word for wordas clause 3.8.1.14“Falls in shower floors”. It says:The entire shower areamust be constructed so that water flows to the waste without ponding.It then provides the following explanatory information:1. The ratio of fall achieved in a floor may vary depending on the following:(a) finished height requirements at doorways(b) height of fixtures or fittings(c) dimensions of the tiles used; adequate falls become more difficult to achieve as the size of tiles increases.(d) area of the floor to be drained(e) requirements of persons with a disability2. The recommended ratio of fall within showers is between 1:60 and 1:803. The recommended ratio of fall in other wet areas is between 1:80 and 1:100.4. In some cases the fall in the floor finishes in the same area may vary.5. Where falls steeper than 1:100 are not achievable, the effectiveness of the floor drainage should be confirmed to ensure that water does not remain on the finished floor in a manner that can adversely affect the health and amenity of the building occupants or deteriorate building elements.Unfortunately, neither the BCA nor AS3740 provide a definition of ponding. Therefore, in an effort to provide an objective measure of when ponding that breaches the intention of the BCA has occurred, I havedeveloped the following definition. •“Ponding can be said to occur when an area of more than about 400 square centimeters of water remains on any single area of the