Queensland Sheet Metal have PVC downpipes suit both industrial and residential buildings. The standard size PVC downpipes that Queensland Sheet Metal provide are 90mm and 100mm. All PVC downpipe accessories are available too.
As a general guide, in non cyclonic areas, for every 1m² of roof area drained, 70mm² of downpipe is required. This calculation is based on the assumption that the maximum rainfall does not exceed 125mm per hour.
It is considered the best practice to drain to different points, using smaller downpipes rather than to one large outlet. Where possible, downpipes should be spaced at not more than 12000mm centres.