Browse Forums General Discussion 1 Apr 06, 2020 4:02 pm Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Hi, looking for some advice regarding downpipes. We just finished our plan presentation and I noticed that in our western elevation we only have 2 downpipes. There are 2 more diverting from the upper roof draining into the ground floor roof but then this is only split between the 2 downpipes at either ends. The length of the ground floor roof is around 19 meters and the distance between the edge of the roof to the first floor wall is around 2.5 meters. Do I need another downpipe added maybe around the middle? Thanks. Re: Do I need another downpipe? 2Apr 06, 2020 4:45 pm Impossible to say given that no relevant information has been posted. The current downpipes are also not well positioned,..aesthetics subjugating function. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Do I need another downpipe? 3Apr 06, 2020 6:07 pm SaveH2O Impossible to say given that no relevant information has been posted. The current downpipes are also not well positioned,..aesthetics subjugating function. Thanks for the response. What info do you require and I'll do my best to try and get them. As for the downpipes positioning, is there a position that is always preferred for function or do I have to wait until plumbers start looking at it and depend on them to suggest the positioning and the need for extra downpipes? Re: Do I need another downpipe? 4Apr 06, 2020 11:00 pm jedigriever What info do you require and I'll do my best to try and get them. Unfortunately, your opening post's question is not as easy to answer as it may first appear. I'll give you some basic details and explanations to give you some grounding on roof drainage design. Eaves gutter compliance can be satisfied by adherence to either the Australian Standards (AS 3500.3) which is a Deemed To Satisfy (DTS) provision referenced in the National Construction Code (NCC) or by referencing 3.5 in Part 2 of the Building Code of Australia (BCA) which is also Part 2 of the NCC. You can download the NCC free of charge. The BCA Part 2 3.5 Roof and Wall Cladding is not recognised in Victoria because of the Victorian Building Authority (VBA) implementing a variation within the Plumbing Code of Australia (PCA) under Part D1 to remove the BCA as a DTS requirement for roof drainage installations. The PCA is also Part 3 of the NCC. I know that you are in NSW but I mention the VBA variation because I want to draw your attention to the BCA Part 2 3.5 roof drainage provisions being laxer when compared to the AS, the reason for the VBA variation. Because you are building a project home, your house will most probably be designed to the lesser BCA provisions unless you have entered into the contract that the AS 3500.3 is to be used and not the BCA. If not, then I can only comment on compliance to the lowest denominator. It must also be understood that compliance does not ensure good design but the overriding factor is that the installation must meet the needs of the NCC's Performance Requirements which have hierarchy. Unfortunately, this is something that builders and their trade persons often do not understand or choose to ignore. The gutters are sloped with high and low points with the downpipes being fitted at the low points and the high points determining the roof areas drained to each downpipe. You also have abutting walls which also have to be drawn into the calculations for roof drainage compliance to account for wind driven rain. Your roof slope also need to be factored for wind driven rain, for example, your 25 degree roof slope shown on the diagram subject the roof catchment areas to a multiplier of 1.23. To assess your roof drainage eaves gutter and downpipe compliance, I would need to know your region's 1:20 Average Recurrence Interval (ARI), your roof slope...(25 degrees), the abutting wall areas, the roof areas draining to each downpipe plus the eaves gutter and downpipe sizes. jedigriever As for the downpipes positioning, is there a position that is always preferred for function or do I have to wait until plumbers start looking at it and depend on them to suggest the positioning and the need for extra downpipes? This is a really interesting question as it brings up a fair bit of history of endemic poor roof drainage practices. The "High Front Guttering Advisory Committee Report on the review and use of high front guttering in New South Wales" (January 2011) may interest you as it also discussed how architects most often draw downpipes as nominal inclusions for aesthetic needs which is then left to the installer further down the food chain to design the installation for compliance. This is why display homes to this day rarely have downpipes visible from the street and why they are positioned at the end of walls for aesthetics even though the largest roof catchment areas are away from the end of the walls...as your's are and where your downpipes have been nominally positioned. https://www.fairtrading.nsw.gov.au/__data/assets/pdf_file/0010/369955/High_front_guttering_advisory_committee_report.pdf https://www.smh.com.au/national/nsw/hidden-report-confirms-gutter-debacle-20110725-1hx55.html Plumbers invariably install to the plan and the Building Surveyor will then sight and accept the plumbers Certificate Of Compliance as proof of compliance. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Building Standards; Getting It Right! It's all good. You can get both wye piece and the coupling with or without thread. 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