Roof drainage systems should be designed and detailed by a suitably qualified trade or professional in accordance with the bca and the australian standards.
Box gutter sizes australian standards.
Calculators for designing eaves gutters box gutters downpipes pipes and open channels etc to australian standards.
And the provision of appropriate overflow devices.
The minimum size of a sump is 400mm x 200mm minimum width of box gutter and 150mm deep.
Plumbers must install the box gutter system in accordance with as nzs 3500 3 as nzs 3500 5 hb 114 and hb 39.
And project managers must ensure that the building is constructed in accordance with the approved design.
Box gutters must be straight no bends.
For commercial projects the minimum allowable width is 300mm.
How to design box gutters to the australian plumbing code as nzs 3500 3 2015.
Sumps are to be appropriately sized in accordance with as nzs 3500 3 with a minimum length of 400 mm and when fitted with a high capacity overflow device with a depth of not less than 150 mm when either one or two box gutters enter the sump.
Quantity and placement of downpipes.
This is a video of a google slides presentation available here https docs.
Code box gutter requirements the minimum width allowed for domestic projects is 200mm.
Building permit involving the box gutter system relevant building surveyor.