Why gutters overflow (and what to do about it)
Overflowing gutters are usually easy to diagnose and fix. Here's the field guide.
Most common causes
1. Blocked downpipes or gutters
Leaves, moss, bird nests, tennis balls. The fix is clearing them out and installing guards.
2. Insufficient gutter fall
Gutters need a 5-10mm fall per metre towards the downpipe. Sagging brackets or house settlement can cause back-fall where water pools and overflows.
3. Gutter capacity too small
Older 4-inch gutters struggle with modern intense rainfall. 5-6 inch gutters handle more.
4. Downpipe blockages at ground level
Where the downpipe enters the drain, leaves can compact and cause a backup. Usually fixable with a drain rod.
5. Eaves alignment
If the lowest row of tiles overhangs the gutter too much, water overshoots. If too little, water runs behind the gutter into the soffit.
When to call a roofer
DIY works for: clearing debris, checking brackets, testing downpipe flow.
Call a roofer for: realigning sagging gutters, replacing sections, fitting larger capacity, fixing persistent overflow at eaves.
A gutter clean is usually £60-£120. Replacing a full gutter system on a Wimbledon semi is £600-£1,200. Both small jobs that prevent much bigger ones.