Why Gutters Overflow and How to Fix It

Cause 1: the gutter is too small

A monsoon downpour sends a lot of water off a roof very quickly. If the gutter is undersized for the roof area draining into it, water spills over the front edge even when the gutter is perfectly clean.

The fix is a larger gutter profile, or more outlets so each length of gutter carries less water.

Cause 2: no fall

Gutters need a slight slope towards each outlet. If the gutter was set dead level, or brackets have moved over time, water sits in the gutter and overflows at the low point.

Re-setting the brackets to a string line restores the fall. Sometimes an extra outlet in the middle of a long run helps too.

Cause 3: too few downpipes

Too few downpipes is one of the most common reasons gutters overflow. Every metre the water has to travel along the gutter adds to the load at the outlet. Adding a downpipe shortens that distance and lets the gutter empty faster.

When it really is a blockage

Leaves, seeds and dirt collect at outlets and corners, especially under trees. Clear them before the rains, check that water runs freely down each downpipe and consider leaf guards where branches overhang.

Repair or replace?

Joints, brackets and outlets can usually be repaired. Replacement makes more sense when:

• The gutter is rusted through in several places
• The profile is too small for the roof
• Brackets have failed along most of the run
• Matching parts are no longer available

How to spot the cause yourself

Watch the gutter during heavy rain from a safe place on the ground. Water spilling evenly along the whole front edge points to an undersized gutter. Water spilling at one low point suggests the fall is wrong. Water backing up near the outlet often means the downpipe is blocked or there are too few of them.

Send us photos

Photos of the roof edge, the gutters and any overflow marks on the wall tell us a lot. Send them on WhatsApp with your location and we will suggest the fix.