Why are my gutters overflowing?
Overflowing gutters are commonly caused by leaves, moss or debris, blocked downpipes, damaged joints, incorrect falls or insufficient drainage capacity. Repeated overflow can soak walls, fascia boards and roof edges, so it should not be dismissed as only a gutter-cleaning issue.
Common causes of overflow
Most overflows come down to blockage, fall or capacity. Leaves, moss and grit collect at outlets; brackets sag so water sits rather than runs; or joints open up and let water escape before it reaches the downpipe.
Overflow at the same spot every time usually points to a local blockage or a dropped section. Overflow along a whole run in heavy rain more often points to fall or capacity.
Why it matters to the roof
Water spilling behind a gutter soaks fascias, wall heads and the bottom course of the roof — exactly the components you do not want permanently wet. Over time that shows as rotten timber and damp inside the wall rather than a dramatic leak.
Clearing and checking gutters is the cheapest maintenance on any house, and it prevents a category of damage that is expensive to put right.