Box Gutter Overflow Design

Holes through the splash guard and the gutter.

Box gutter overflow design.

All domestic box gutters must be a minimum of 200mm wide and 75mm deep. You can find these precut gutter splash guards about 3 in brown and white aluminum at a home center but you could easily make your own out of aluminum or sheet metal and spray paint them to match your gutters. Box gutters sit within the façade or structure of the building. Eaves gutters form the outer perimeter of the roof and their shape allows excess water in high rainfall events to safely overflow over the outside lip of the gutter.

The hydraulic capacity of the overflow device must be no less than the design flow for the associated box gutter outlet. Overflow box gutters must have independent overflow provision discharging to the atmosphere. Failing to install appropriately designed box gutters and correctly sized and positioned overflow devices can lead to serious damage to buildings and contents especially in shed and flat house roof designs often resulting in hefty insurance claims which are a total burden. Outlets box gutter outlets must discharge through either a rainhead or sump.

This effectively states that all box gutters must allow for 30mm of freeboard which is from the overflow point eg. Overflow devices need to discharge to the atmosphere in such a way as to prevent damage to buildings and property. Eaves and box gutters. 2015 3 7 4 layout.

Making the box gutter wider will also reduce the box gutter depth. Drill rivet holes for the gutter splash guard. This is very important so that water will overflow externally to the building rather than flood into the roof cavity. A wider overflow needs less depth of overflow hence the box gutter depth will also be reduced.

The box gutter depth and the sump length are influenced by the size of the overflow. Roofs may be constructed with or without gutters. There will also be an overflow facility on the side or the end. A good box gutter design will have falls along its length together with sumps to collect water before it is fed into large downpipes.

Rainhead overflow or specific box gutter overflow must be at least 30mm below the height of the back of the box gutter. However a wider overflow may increase the length of the sump. There are two categories of gutters.