Box Gutter Overflow Requirements

If draining to a sump with a vertical overflow somewhere along the box gutter use this calculator.

Box gutter overflow requirements.

The hydraulic capacity of the overflow device must be no less than the design flow for the associated box gutter outlet. This effectively states that all box gutters must allow for 30mm of freeboard which is from the overflow point eg. The width of the rainhead is to be at least equal to the width of the box gutter and the box gutter needs to be sealed to the rainhead. The minimum width allowed for domestic projects is 200mm.

Overflow devices need to discharge to the atmosphere in such a way as. Hang the gutter lower the top of the bead must be 20mm below the top of the fascia to allow water to overflow safely over the bead. Use a 10mm spacer this creates a gap behind the gutter so water can overflow freely. Box gutters must be straight no bends.

The vba has provided several options for plumbers to make an installation compliant. Have a sole width which is not reduced discharge at the downstream end without. Trial box gutter width the minimum width allowed for domestic projects is 200mm. Rainhead overflow or specific box gutter overflow must be at least 30mm below the height of the back of the box gutter.

However any width can be entered. Have a minimum depth of 75mm at the high end. For commercial projects the minimum allowable width is 300mm. All domestic box gutters must be a minimum of 200mm wide and 75mm deep.

Sides must be vertical.