Browse Forums Building Standards; Getting It Right! 1 Nov 25, 2014 7:52 pm Just start this topic, so we can learn from the experts
here is response from my builder regarding downpipes (Melbourne south east) our gutter is Quad Gutter, slotted, I think it is standard Lysaght 115mm quad gutter, but will ask builder to confirm. Down pipes 100mmx50mm, roof pitch 22.5 • Downpipes cannot be spaced more than 12 meters apart. • Downpipes have a limit of 50 sqm per downpipe • The area of your roof space is 280.58 sqm • The roof catchment space is 331.0844 sqm o Please see my calculations below o 331.0844 / 50 sqm = 6.6 o Based on these calculations you will need 6.6 downpipes to manage the water flow. • Currently you have 8 down pipes. • Each one of your down pipes will be capable of 41.38555 sqm. Re: Downpipes general discussion 2Nov 26, 2014 11:25 pm fzxbeetle Just start this topic, so we can learn from the experts here is response from my builder regarding downpipes (Melbourne south east) our gutter is Quad Gutter, slotted, I think it is standard Lysaght 115mm quad gutter, but will ask builder to confirm. Down pipes 100mmx50mm, roof pitch 22.5 This is a good topic for discussion because stormwater and roof drainage is a common area of non compliance in the building industry that most often slips past inspections. fzxbeetle here is response from my builder regarding downpipes •Downpipes cannot be spaced more than 12 meters apart. Prior to May 2007, the Building Code of Australia (BCA) stated: The spacing between downpipes must not be more than 12 m. This was revised on the 1st of May, 2007 to... “3.5.2.5 Downpipes - size and installation Downpipes must - (a) not serve more than 12m of gutter length for each downpipe; and (b) be located as close as possible to valley gutters and, if the downpipe is more than 1.2m from a valley, provision for overflow must be made to the gutter; and (c) be selected in accordance with the appropriate eaves gutter section as shown in Tables 3.5.2.2.” In effect, the above meant that two downpipes each serving 12 metres of gutter could be fitted at either end of a 24 metre long verandah, i.e., 24 metres apart. It also confused building surveyors and others because many thought that the gutter length served defined compliance, not adherence to the maximum allowable roof area drained. On May 1 2013, the BCA was amended to once again state "The spacing between downpipes must not be more than 12 m." Australian Standards - AS/NZS 3500.3 Stormwater Drainage does not stipulate a 12 metre maximum distance between downpipes nor does it regulate a maximum 12 metre gutter length served by one downpipe. Eaves gutter roof drainage is best installed in accordance with AS/NZS 3500.3:2003 Stormwater Drainage, a Deemed To Satisfy (DTS) document referenced by the BCA but the BCA regs are often used in lieu of the more refined Australian Standards. The BCA 12 m rule means little at any rate as either the AS or the BCA can be quoted whenever suited as DTS solutions can include mixes of both the BCA and AS! HOWEVER, the Victorian Building Authority (VBA) has a variation in the Plumbing Code of Australia (PCA) under Part D1 that removes the BCA as a Deemed To Satisfy (DTS) requirement for roof drainage installations in Victoria. The PCA is also Part 3 of the National Construction Code (NCC); The BCA is Parts 1 and 2. I will wait for confirmation regarding the gutter make and type plus the cross sectional area before giving a further reply. The maximum roof area figures your builder has quoted that your downpipes can drain would require a minimum gutter cross sectional area of 6,600 sq mm and minimal 75 x 50 mm rectangular or 90 mm round downpipes if AS/NZS 3500.3 is being used by the builder as required in Victoria. Many people may look at the builder’s terminology and the figures posted by fzxbeetle and not understand them or know how the roof drainage areas are calculated. The following should help. Firstly, downpipes fitted to houses DO NOT drain equal roof areas. AS/NZS 3500.3 is a Deemed To Satisfy (DTS) manual for roof and stormwater drainage. It calculates eaves gutter compliance by using the region's 1:20 Average Recurrence Interval (otherwise known as a 1 in 20 year storm event), the gutter’s cross sectional area, the roof slope and the downpipe size to determine the maximum roof area that can be drained to each downpipe. Melbourne's 1:20 Average Recurrence Interval (ARI) is shown in AS/NZS 3500.3 as 130 mm/hour. The ARI is based on a 5 minute rain intensity and Melbourne's 5 minute average intensity is 2.1666 mm/min. Note that the BCA DTS provisions use a lesser 1:20 ARI of 127 mm/hr. There is a new method called an Intensity Frequency Duration (IFD) that takes statistics from over 4,000 weather stations and the more location accurate IFD is now preferred by many rather than the more regional ARI. Bashworth has some details on his blog plus I have explained it previously (with links) on Homeone and the posts can be found by using the forum's search facility. The gutter's cross sectional area (that determines the gutter's carrying capacity) is measured from 10 mm below the gutter's lowest wall or from 10 mm below the slots when a slotted gutter is fitted. The roof slope is subject to ‘factoring’ to allow for wind driven rain. For fzxbeetle’s 22.5 degree roof slope, the factoring is 1.21. The builder has referred to “roof space” and a larger figure as “catchment space”. Roof space is the roof plan area as seen from above and the catchment space is the factored roof area. If you multiply the smaller roof space figure by 1.21, you will arrive at the larger roof catchment figure. Any wall abutting a lower roof must also be included in that lower roof's catchment calculations (to allow for wind driven rain) as is the area of gutter overhang. Gutters MUST be able to drain without overflowing during a minimum qualifying 1:20 ARI. This includes slotted gutters but oddly enough, many people think that a slotted gutter overflowing is ok. It isn't! Despite this, the BCA performance requirements do not state that eaves gutters must not overflow during rain intensities up to a minimum 1:50 ARIs, the next highest rain intensity bracket. Many new houses have gutters that overflow during rain intensities that are below even a minimum 1:20 ARI due to poor downpipe positioning yet the roof drainage is still (often) compliant! EDITED: Had written 75 x 70 mm downpipe instead of 75 x 50 mm downpipe. Now corrected. 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: Downpipes general discussion 3Nov 26, 2014 11:34 pm SaveH2O... thank you for that wonderful explanation. Re: Downpipes general discussion 4Nov 27, 2014 12:14 am Thanks tlb. Being an erudite gentleman, you may be interested in the 2011 Report to the NSW Parliament that I have linked below and I refer in particular to Operation Flow on pages 17-18 and the section 11 text on page 27. http://www.fairtrading.nsw.gov.au/pdfs/ ... report.pdf 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: Downpipe Compliance - general discussion 5Nov 28, 2014 8:55 pm Hi fzx, As you are still waiting for confirmation about your gutters and as I am going to be unavailable for the next few days, I will answer your questions in full based on your belief that you will have the Lysaght 115 mm slotted Quad gutter. fzxbeetle our gutter is Quad Gutter, slotted, I think it is standard Lysaght 115mm quad gutter, but will ask builder to confirm. Down pipes 100mmx50mm, roof pitch 22.5 The Lysaght 115 mm slotted Quad gutter's cross sectional area is 5,225 sq mm as per table 2, page 5 of the document linked further below. http://www.lysaght.com/files/dmfile/Lys ... p2014b.pdf Note that some information in the Lysaght document is not accurate, for example, the Melbourne 1:20 ARI is shown as 127 mm/hr and the roof slope factoring determination is incorrect. This is because they have used the BCA figures which have never applied in Victoria. For compliance with AS/NZS 3500.3, the maximum (1.21 factored) 22.5 degree pitch roof area (referred to by your builder as roof catchment space) that this gutter and a 100 x 50 mm downpipe can drain in a 130 mm/hr 1:20 ARI region is about 38 sq m. This is a 31.4 sq m roof plan area (referred to by the builder as roof space). 331 ÷ 38 = about 8.7 downpipes. This calculation assumes that the gutter will have a 1:500 or steeper gradient. fzxbeetle here is response from my builder regarding downpipes • Downpipes have a limit of 50 sqm per downpipe This information from your builder is ambiguous as it does not specify a gutter or downpipe size but it has to be accepted that the builder is referring to your gutter and downpipe sizes and your factored (roof catchment space) as they have stated elsewhere in their calculations. The statement and calculations they give do not apply to the Lysaght 115 mm slotted Quad gutter. As mentioned in a previous post, their above statement would apply to a gutter with a minimum cross sectional area of 6,600 sq mm and fitted with either 75 x 50 mm rectangular or 90 mm round downpipes. fzxbeetle here is response from my builder regarding downpipes • Each one of your down pipes will be capable of 41.38555 sqm. The above figure refers to the roof plan area (multiplying by 1.21 will give you 50 sq m). The calculation is not commensurate with the Lysaght 115 mm slotted Quad gutter. If the builder is installing Lysaght 115 mm slotted Quad gutters fitted with eight 100 x 50 mm downpipes to drain your roof area, the installation will not comply with AS/NZS 3500.3 Stormwater Drainage. If you are also having a water tank as a part qualifier for the Victorian 6 Star Standard, the downpipes need to be uPVC 90 mm round. EDITED: Added why the Lysaght table figures are not accurate. 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: Downpipes general discussion 6Dec 04, 2014 8:26 pm Below is a link to a document titled "Roof plumbing – roof drainage systems" by the NSW Department of Fair Trading. http://www.fairtrading.nsw.gov.au/pdfs/ ... _guide.pdf NOTE: The Office of Fair Trading guide is based on the former Victorian Plumbing Industry Commission’s Roof Plumbing Technical Solution Sheet 0.04. This is why the roof drainage calculation example uses the Melbourne 1:20 ARI of 130 mm/hr rather than the much higher Sydney 1:20 ARI of 210 mm/hr. The example used has... 1. A 6,125 sq mm gutter cross sectional area. 2. 130 mm/hr 1:20 ARI. 3. 100 x 50 mm rectangular downpipes. 4. A 1:500 gutter slope. 5. A 23 degree roof pitch. The example has the same specifications as fzxbeetle's specifications except that the example's gutter cross sectional area is about 17% larger. The example's gutter and downpipes have been calculated as compliant to harvest a maximum factored roof area of 47 square metres. The example's roof plan area is 185 sq m and the factored (x 1.21) roof catchment area is 223.8 sq m. 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: Downpipe Compliance - general discussion 7Dec 06, 2014 8:33 pm I am still waiting for any detail from Henley regarding my roof drainage design. The construction manager just keep telling me the gutter is standard gutter, and have no idea what is cross sectional area I suspect Henley will just tell me their design has plumbing compliant certificate and it should be fine sick of Henley now. won't recommend them to anyone here......... Re: Downpipe Compliance - general discussion 8Dec 06, 2014 8:47 pm The gutter is a standard gutter but it and the downpipe must be compliant for the maximum roof area drained, their claim of compliance for a 50 sq m roof catchment area for the (small) gutter discussed is nonsense if they are using AS/NZS 3500.3. EDIT: I think that it can be taken at this point that your builder is not using AS/NZS 3500.3 as mandated and are wrongly using BCA 3.5.2.2 that is NOT COMPLIANT for use in Victoria as previously explained. NOTE: BCA Part 3.5 - Roof and wall cladding - 3.5.2.2 shows that a 115 mm D gutter and a 100 x 50 mm downpipe are compliant to drain a maximum 50 sq m roof harvest area in an area where the rainfall intensity as per BCA table 3.5.2.1 is up to 160mm/hr. EDIT 15/05/2016 New home buyers in other States should seriously consider which Standard they have written into their contract. 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: Downpipe Compliance - general discussion 9Dec 06, 2014 11:24 pm You can view the section of the BCA about downpipes and gutters on my blog. http://bendigowaldorf.blogspot.com.au/2 ... s-and.html Re: Downpipe Compliance - general discussion 10Dec 06, 2014 11:28 pm The catchment area slope factor for eave gutters is... Re: Downpipe Compliance - general discussion 11Dec 08, 2014 5:55 pm fzxbeetle I am still waiting for any detail from Henley regarding my roof drainage design. The construction manager just keep telling me the gutter is standard gutter, and have no idea what is cross sectional area I suspect Henley will just tell me their design has plumbing compliant certificate and it should be fine You need to ask Henley whether they have designed the stormwater drainage in accordance with AS/NZS3500.3:2003 or whether they have used an Alternative Solution. If they have used an Alternative Solution, you then need to establish what that Alternative Solution is and whether it is certified for use in Victoria. The figures they have provided for your house are not compliant with AS/NZS 3500.3. No question! I have received the following written confirmation from a senior person in the Victorian Building Authority - Plumbing. "Plumbing practitioners in Victoria are required to install roof drainage installations in accordance with AS/NZS 3500.3 Plumbing and drainage Part 3: Stormwater drainage the relevant section of AS/NZS 3500.5 Plumbing and drainage Part 5: Housing installations as prescribed in the National Construction Code Volume Three - Plumbing Code of Australia (PCA) along with HB39 – 1997 Installation code for metal roofing and wall cladding and SAA/SNZ HB114:1998 Guidelines for the design of eaves and box gutters as prescribed within the Plumbing Regulations 2008. This is as a result of the VBA implementing a Victorian variation within the PCA under Part D1to remove the BCA as a Deemed to Satisfy requirement for roof drainage installations." There are many unsavoury aspects to the BCA Acceptable Construction Practice 3.5.2.3 and 3.5.2.4 and 3.5.2.2 tables (a), (b) and (c) posted below. I will go over just a few. As per fzxbeetle's house, the BCA deems that his gutter and downpipes can harvest a 50 sq m roof catchment area, the AS calculation shows a maximum roof catchment area of about 38 sq m. fzxbeetle's gutter cross sectional area is 5,225 sq mm and would be considered in table 'b'. as gutter type C. Table 'a' shows that in a 140 mm/hr ARI area, a 50 sq m roof catchment area can be serviced by either gutter types A or C as designated in table b. Table b shows that gutter type C must have a minimal cross sectional area of 5,200 sq mm and gutter type A must have a minimum cross sectional area of 6,500 sq mm. My question is "why does the smaller gutter have the same roof harvest area compliance as the bigger gutter? One more (of many others) to ponder about..... The biggest gutter shown in table b is type E with a minimum cross sectional area of 9,000 sq mm. Table c shows that a 100 x 50 mm rectangular downpipe can be used with a type E gutter and table a shows that a type E gutter can drain a 70 sq m roof harvest area in a 175 mm/hr ARI region. In comparison, the Australian Standards calculations show that a 9,000 sq mm cross section gutter must as a minimum be fitted with either a 100 x 75 mm rectangular or a 100 mm round downpipe and in a 175 mm/hr ARI area, it can only service a maximum roof harvest area of 55 sq m. 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: Downpipe Compliance - general discussion 13Dec 09, 2014 9:28 pm I would certainly make it formal and something along the lines of what is below. Heading # ##### ###### Dear ########## I have concerns with the claims ###### has supplied me about the roof harvest area that my downpipes can service. It is my understanding that my downpipes will be 100mm x 50mm rectangular and the gutters will be the Lysaght 115mm quad slotted gutter. I believe that this gutter's cross sectional area is 5,225 sq mm. The information I was given by ####### stated that the downpipes can service a 50 sq m roof catchment area and a 41.38555 sq m. roof space. I have since received information that those claims are not compatible with the calculations as per AS/NZS 3500.3:2003 Plumbing and drainage part 3: Stormwater Drainage if the 100mm x 50mm downpipes service the Lysaght 115mm quad slotted gutter. Can you please clarify the following: 1: Confirmation that my downpipes are designated to be 100mm x 50 mm rectangular and the gutters to be the Lysaght 115mm quad slotted. 2. Will my roof drainage installation be installed as required in Victoria in accordance with AS/NZS 3500.3 Plumbing and drainage part 3: Stormwater drainage? 3. Are your calculations based on a BCA Alternative Solution and Tables a, b and c in BCA 3.5.2.2 and if so, are you aware that the Victorian Building Authority has implemented a Victorian variation within the Plumbing Code of Australia under Part D1 to remove the BCA as a Deemed to Satisfy requirement for roof drainage installations? Thanking you for your anticipated early response, Yours etc... 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: Downpipe Compliance - general discussion 14Dec 09, 2014 10:05 pm Thanks I also request them to reply formally in writing regarding site drainage and DPC hopefully I can get something and will post it here 1 according to your previous email, our site drainage storm water pipes are single DN 100mm. please confirm whether the drainer use 100mm or 90mm on our site, and confirm if flexible connector has been used according to engineer plan and our tender. single DN 100mm pipe can only drain max flow capcacity of 450lpm as per AS2200 dring a 1:20 ARI. our roof catchment space is 331.0844 sqm, 1:20 ARI is 130 mm/hr, giving an average 5 minute rain intensity of 2.1666 mm/minute. the flow off our roof is caculated as 331.08x2.1666 =717lpm . again our site drainage of single DN100mm pipe connected to LPOD wont compliant with AS2200. 2 according to AS3700 and Austral bricks, DPC should be visible, however , Henley next gen spec do not compliant with this, please confirm in writing this is acceptable alternative solution, and certified by building surveyor in Vic. please provide evidence of this. Re: Downpipe Compliance - general discussion 15Dec 09, 2014 10:51 pm The link below is a QLD Government document that simply explains the AS2200 calculations. There is not much else available on the net unfortunately. A lot of industry 'professionals' unfortunately have no knowledge of this Standard. http://www.dsdip.qld.gov.au/resources/n ... er/136.pdf The concern I have with your house as per another thread is... 1. You need 2 x 100mm pipes to service the house stormwater drainage and pits. 90 mm PVCu stormwater pipes will not be compliant as per AS2200 provided that AS2200 is referenced in your contract. Nevertheless, the plumber should still be aware of the pipes capacities as per AS2200 and use his professional best judgement in the system's design. 2. The two 100mm pipes should not connect to a single 100mm PVCu pipe because the combined flow capacity during a 1:20 ARI will be excessive. Re the 130mm/hr ARI, this is as per the Australian Standards. Henley have used a lesser 127mm/hr for your roof drainage calculations as per the BCA Table 3.5.2.1. It would be wise to communicate in writing and be aware that the ARI for the roof drainage is 130mm/hr, not 127mm/hr as stated in the BCA. The BCA is NOT REFERENCED in Victoria for stormwater drainage. I am not aware of an Alternative Solution for AS2200 and would be surprised if there is. I actually think that the mathematics used for AS2200 are faulty in any case because they don't calculate flow rates as per the pipe's true internal diameter, only the nominal diameter (DN). I have copied the text below off another post on another thread. You might find it interesting but regulations are regulations and compliance is compliance...no matter what common sense suggests. The 100 mm uPVC SN6 DWV pipe has an internal volume (8.53 litres per metre) that is about 46% greater than the common use 90 mm uPVC stormwater pipe with 1.8 or 1.9 mm walls and an internal volume of 5.84 litres per metre. This is because the 90 mm stormwater pipe has an internal diameter (ID) of 86.2 mm whereas the much stronger (3 mm thick walls) 100 mm SN6 DWV pipe has an ID of 104.2 mm. AS2200 requires the nominal diameter 100 mm uPVC DWV pipe to have a maximum flow rate of 450 lpm (which is 0.88 metres per second) whereas the flimsy nominal diameter 90 mm uPVC stormwater pipe is mandated as 360 lpm (which is 1.03 metres per second). A bit strange one might say! When you do the calculations for pipes with a true 90 mm ID and a 100 mm ID, the respective internal volumes are 6.36 and 7.86 litres per metre.This in turn equates to respective flow rates of .94 and .95 metres per second when flowing at 360 and 450 litres per minute. Taking this further... If the 90 mm (86.2 ID) uPVC stormwater pipe was mandated for a maximum flow rate of .94 metres per second, the litres per minute flow rate would be 5.89 x .94 x 60 = 332 litres per minute, not 360! If the 100 mm (104.2 ID) uPVC SN6 DWV pipe was mandated for a maximum flow rate of .95 metres per second, the litres per minute flow rate would be 8.53 x .95 x 60 = 486 litres per minute, not 450! It is my opinion that the calculations for 90 mm ID and 100 mm ID uPVC pipe should not be transposed to nominal sized 90 mm uPVC stormwater pipe and 100 mm uPVC SN6 DWV pipe. The standards should, in my opinion, apply to the pipe's true ID and not their nominal ID, indicated as DN. The pipe's strength should also be taken into account. Farcical situations such as highlighted here where thin walled DN90 (actual ID is 86.2 mm) PVC stormwater pipe is understood to have a 17% higher velocity rating (1.03 metres per second) than the considerably stronger DN100 (actual ID is 104.2 mm) PVC DWV pipe (.88 metres per second) should never happen. EDIT: AS2200 now shows DN 100mm pipe to now have a flow rate of 480 lpm with a 1:100 gradient. Plumbers should consult AS2200 when designing stormwater flow capacities but few do. This allows under capacity systems to be installed yet those systems are still deemed to meet 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. Re: Downpipe Compliance - general discussion 16Dec 10, 2014 8:22 am Jiminy ! That does seem to be a very bad error on their part SaveH2O. If the regulators can't even get the basics right what hope has the average plumber out on site got ? Stewie Re: Downpipe Compliance - general discussion 17Dec 10, 2014 3:53 pm Question... not related to the drainpipes, but to the stormwater pipes that they are connected to. Our builder has admitted that our stormwater discharge pipe runs uphill to the legal point of discharge. The LPOD is 300mm above the stormwater pipe. How do they fix that? Re: Downpipe Compliance - general discussion 18Dec 10, 2014 4:38 pm Pumped systems require two pumps set up to operate alternately at each start and there are a number of regulations concerning high level sirens, minimum pit size etc. The regs are covered in AS3500.3 section 9. The best alternative is to have a charged detention system. Your place would be best served by having 2 interconnected but spaced tanks. Your other existing problem is the ag drainage. The design problem is the site cut levels, not the LPOD. I hope that they don't expect you to pay for their mistake, their social conscience should decree that they compensate you but good luck with that one! 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: Downpipe Compliance - general discussion 19Dec 10, 2014 9:23 pm If you want to download the ARI tables from AS3500 please visit: http://goo.gl/6bsB29 Re: Downpipe Compliance - general discussion 20Dec 11, 2014 6:33 pm Finally, Henley agree to add another two downpipes to compliant with AS3500. Well done, SaveH2O, Thanks Henley believe our site drainage is ok and they refer to below document to support their claim http://www.vba.vic.gov.au/__data/assets ... utters.pdf 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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