Sumps

Sumps must be at least the same width as the gutter and have an outlet positioned below the sole of the gutter to increase the head of water at the outlet.

Sump – Same Width as Gutter

Sump, Same width as the Gutter

 

Internal sumps must have overflows. These are often a secondary pipe overflow, with the outlet height positioned above the level of the primary outlet. Internal sumps must also be sealed against the sides and sole of the gutter.

Sump with Obvious Overflow

Sump with Overt Overflow

 

An internal sump should have a guard that prevents debris from blocking the outlet. A removable aluminium expanded-metal box can be fitted at a minimum of 40 mm below the sole of the gutter. Because the top is flat, it is unlikely that the entire surface area of the outlet can become blocked, so it is preferable to balloon-type guards. A leaf guard should have a horizontal surface area of at least four times the size of the downpipe outlet area and should be installed at roughly mid-height of the sump depth. Gratings can cause sump blockage, and this can reduce the outlet capacity.

Sump with a Leaf Guard

Sump with Leaf Guard

 

Gratings or guards should be designed so that any debris will float, and hail, or obstructions, such as a tennis ball, will not wedge and block the guard. Gratings or guards should be cleared of accumulated debris regularly as part of normal maintenance.