When one box gutter empties into another

In short: Box gutter failures discharge inside the building, which is what makes them different.

What a box gutter is

A gutter that runs inside the roof instead of along its edge, moving water out of sight.

One box gutter discharging into another, along with sump and overflow provision that did not match the roof above.

The receiving gutter was sized for its own catchment. Adding another roof area to it means it runs full in a storm it was never designed for.

A high capacity overflow exists so that a blocked sump becomes a visible nuisance outside rather than water inside the ceiling.

A drone pass, and direct access where it is safe. None of this is visible from the ground.

Written by the Owner Inspections team from inspections carried out in Box Hill. Licensed building practitioners, NSW Fair Trading licence 366177C.

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Questions Box Hill owners ask about this

Is this a design fault or an installation fault?

It can be either, and the report says which the evidence supports. That distinction matters when responsibility is being allocated.

How urgent is it?

It is a handover item to press hard, because the failure mode is internal water and the fix is far cheaper before you have paid.

Does ponding matter?

Where the gutter is designed to drain and does not, yes. Standing water finds laps and fasteners.

Will I ever notice it myself?

Realistically only during a heavy storm, at which point you are already dealing with the consequence.