![]() The roof areas drained to each downpipe is determined by the gutter's high point (HP) and the HP also determines the gutter's slope.īecause you are having replacement guttering and downpipes, the replacement must meet current compliance. Unfortunately, I still don't know whether the gutters are standard or slotted but I can work around that to answer your queries.Įaves gutter roof drainage compliance references an area's rainfall intensity during a 1:20 Average Recurrence Interval (ARI), the gutter's cross sectional area (carrying capacity), the downpipe size, the roof slope (to factor wind driven rain) and any abutting walls (from an upper roof area) to determine the maximum compliant ' roof harvest area' that can be drained to each downpipe. Not sure which would be the correct way to proceed. There is a clear discrepancy between the roofers recommendation and AS3500. I also see there is a CSIRO method for shorter runs. Can anyone recommend, should I be engaging an engineer to make sure we get the right size gutters and downpipes/connection details or are roofers generally ok to do this sort of thing. Its all become a lot more complicated than I expected. The roofer thinks he is designing to HB 35 which is correct. ![]() We have a 70m2 catchment on each side of the house (rectangular roof, gable ends) with a 30 degree slope going into 1 downpipe. I decided to delve a little deeper and found that AS3500 actually goes into alot more detail than this and that in fact we need a much larger gutter and downpipe to comply with this standard. When I asked what size he was proposing the size he proposed for the gutter is 125mm high front quad. ![]() His response was that all you need is 1 downpipe per 90m2. As a last minute check I asked the roofer about whether he would be undertaking the calculations to make sure the replacement gutters and downpipes are the correct size. We have received a quote to replace the gutters at our place (as wella s replacement of metal roof to extension at the back) and had chosen someone for the work. ![]()
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