Guttering That Overflows in Heavy Rain Is Usually Not Blocked

The single most useful thing you can do is stand outside during the next serious downpour and watch which part of the gutter overflows.

Overflow at one specific point, with the rest of the run coping, points to fall or a sag at that spot. Overflow evenly along the whole length points to capacity, meaning there is more water arriving than the gutter and its downpipes can move.

Overflow at the back of the gutter, running down the wall rather than off the front, is a different problem again and usually means the roof edge or the gutter to fascia detail is wrong.

A gutter is a holding channel, not a drain. All it does is get water to a downpipe, and the downpipes are what actually move it away.

Sydney storms deliver a great deal of water in a short time. A roof with too few downpipes for its area will overflow in a heavy fall no matter how clean the gutters are, because the water simply cannot leave fast enough.

This is the cause that gets misdiagnosed most often, because the obvious response to overflow is to clean the gutters, and cleaning a gutter does nothing for capacity.

A gutter has to run slightly downhill to its outlet. If it is level, or worse, if it runs away from the outlet, water sits in it permanently.

Standing water is a problem in its own right. It holds debris in place, keeps the steel wet and rusts the gutter out from the inside, so a fall problem eventually becomes a replacement problem.

You can usually see it after rain stops. If there is still water sitting in the gutter an hour later, the fall is wrong.

Gutter brackets fix into the fascia, and the fascia on an older house is timber.

If that timber has been sitting behind a rusted gutter it has taken on water, and softened timber does not hold a bracket. The gutter drops between the brackets, holds water at the low point, and overflows there in anything more than light rain.

This is why a sagging gutter is often a fascia job rather than a gutter job. Fitting a new gutter onto rotten fascia gives you a new gutter that will pull loose, so the board underneath has to be dealt with at the same time.

Gutter guard is genuinely useful under trees and largely unnecessary without them.

It earns its cost on a roof that fills with leaf every autumn, particularly where the gutter is difficult or dangerous to reach. It reduces how often the gutters need clearing, and it does not remove the need.

It is worth being clear about that, because guard is sometimes sold as a permanent solution. Fine debris still gets through, and a guard over a gutter with the wrong fall still overflows.

The old gutter comes off, the fascia is inspected and replaced where it has gone, new brackets go on at the correct spacing, and the new gutter is set to fall towards the outlets.

Downpipe positions and quantity are worth reviewing at the same time rather than replicating what was there. If the original roof was under-drained, replacing the gutter without adding a downpipe reproduces the original problem in new steel.

If the roof is being replaced as well, do the guttering with it. The fascia is exposed, the roof edge is being remade anyway, and coming back for it later costs considerably more.