Round downpipes are available in a range of different sizes to suit both domestic and commercial applications. The most common downpipe size used for domestic application is 90mm in diameter. Other custom sizes may also be available on request. Available in a range of UniCote colours, UniZinc, galvanised, stainless steel and copper and they come in 1800mm and 2400mm lengths.
The below formula will provide you with a general indication in non cyclonic areas how much downpipe is required. This is assuming that the maximum rainfall does not exceed 125mm/hour.
Every 1m2 of roof = 70mm2 of downpipe is required.
We recommend draining to different points using smaller downpipes rather than only one large outlet. Downpipes should be spaced at no more than 12000mm centres where possible.
For a more accurate information, please read the Australian Standards – Installation Code for Metal Roofing and Wall Cladding SAA HB39-1997.