Here is a step wise guide for you to help.
Box gutter sump depth.
Choose an available size or any other size and enter that for the calculation of the sump.
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.
The depth shown of the box gutter is the depth at the upstream end.
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.
This is a good size for the required flow.
These options give provisions for overflow to the box gutter.
The minimum depth required for the box gutters that make up this roof drainage system is 125 mm.
The line will correspond to a minimum box gutter depth.
The depth shown of the box gutter is the depth at the upstream end.
The suggested down pipe diameter is shown for reference purposes only.
The outlet must be no further than the diameter of the outlet to the centre of the outlet.
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.
This will give a sump depth about 150mm.
Choose an available dp size or any other size and enter that for the calculation of the sump.