Here is a step wise guide for you to help.
Box gutter sump depth.
The theoretical down pipe diameter is shown for reference purposes only.
The depth shown of the box gutter is the depth at the upstream end.
Choose an available dp size or any other size and enter that for the calculation of the sump.
This is a good size for the required flow.
The outlet must be no further than the diameter of the outlet to the centre of the outlet.
Box gutter gradients shall not be flatter than 1 200 for sole widths equal to or less than 600mm wide.
Sump with high capacity overflow device.
Starting at the gutter gradient intersection draw a line up the design graph for a freely discharging box gutter chart in your copy of the standard.
The depth shown of the box gutter is the depth at the upstream end.
This will give a sump depth about 150mm.
Choose an available size or any other size and enter that for the calculation of the sump.
To determine the box gutter depth is the first and foremost step for sizing components and materials for the roof drainage system which includes the rain heads and the box gutters.
The minimum size of a sump is 400mm x 200mm minimum width of box gutter and 150mm deep.
The suggested down pipe diameter is shown for reference purposes only.
The line will correspond to a minimum box gutter depth.