Most gutters overflow because they are blocked with leaves, moss or silt. Other common causes are blocked downpipes, gutters that have sagged or lost their fall, leaking joints, and gutters too small for the roof they drain. Overflowing water soaks walls and the roof edge, so it is worth finding the cause and fixing it before it leads to damp or rot.
The common causes
Blocked gutters
Leaves, twigs, moss washed off the roof, and silt from tiles all collect in gutters. Once the water can't flow, it spills over the front edge. Gutters near trees can block within a single autumn. Moss is a big culprit on many roofs, which our guide to moss on your roof covers in detail.
Blocked downpipes
If the gutter is clear but water still overflows near the outlet, the downpipe is often blocked, usually at a bend or at the bottom where it meets the drain. Birds' nests and balls on flat roofs can block outlets too.
Sagging or loose gutters
Gutters are held up by brackets screwed into the fascia. If the brackets break, rust or pull out of soft timber, the gutter sags. Water pools in the dip and spills over. Loose gutters are often a sign of rotten fascias, explained in our guide to when to replace fascias and soffits.
Wrong fall
Gutters need a slight slope towards the outlet. If they were fitted level, or have moved over time, water sits in them and overflows in heavy rain.
Leaking joints
Plastic gutters join with rubber seals that harden and shrink with age. Water drips from the joints, which can look like overflowing from the ground. Cast iron gutters can crack or rust at the joints.
Gutters too small for the roof
Some gutters are simply not big enough for the area of roof they drain, especially where an extension or dormer adds extra roof. Water shooting over the gutter in heavy rain, particularly at the inside corner of a valley, is a typical sign.
Valleys and roof details
Where two roof slopes meet in a valley, a lot of water arrives at one point in the gutter. If valleys are blocked with leaves, water can overflow or get under the tiles. Hidden gutters behind parapet walls are harder still, because blockages can't be seen from the street.
Why it matters
Overflowing gutters can cause:
- damp patches on inside walls and ceilings
- stained and green brickwork outside
- rotten fascias, soffits and rafter ends
- water pooling at the foot of walls, which can affect foundations and cause rising damp
- ice forming on paths in cold weather
Checks you can do from the ground
You can learn a lot without climbing a ladder. Next time it rains heavily, step outside and look for:
- water spilling over the front of the gutter, and where along the run it happens
- drips from joints or corners
- gutters that dip or lean away from the fascia
- plants or moss growing out of the gutter
- water gushing from the top of a downpipe or soaking the ground at its foot
- dark, damp patches on the brickwork below
Make a note or take photos. Knowing exactly where the overflow happens helps a roofer find the cause quickly.
How to fix it
Clear and flush
Clearing gutters and flushing downpipes solves most overflowing. A roofer can do this safely from proper access equipment and check the roof at the same time.
Realign and refix
Sagging gutters can be lifted, given the right fall and fixed on new brackets. If the fascia is rotten, it needs replacing first.
Reseal or replace joints
Leaking joints can sometimes be resealed. If the gutter is old and brittle, replacing a run is usually the better fix.
Upgrade the gutters
Where gutters are too small, fitting a deeper gutter, an extra downpipe or a better outlet can solve the problem. Leaf guards help on homes right next to trees, though they still need checking.
Listed homes and conservation areas
On a listed building, replacing cast iron gutters with plastic is likely to need listed building consent, and some conservation areas have extra controls. Check with your local council before changing materials.
Should you clear gutters yourself?
You can clear a bungalow gutter from a ladder if you are confident, with someone holding the ladder. For anything higher, or where the gutter is loose, it is safer to use a roofer.
In Essex, Hertfordshire and Cambridgeshire
Overflowing gutters are especially common in leafy towns and on exposed coastal roofs.
- Forest towns: With Epping Forest on the doorstep, Loughton roofs get a lot of leaves, twigs and moss, and gutters and valleys block. Waltham Abbey, with Epping Forest on one side and the Lee Valley Park on the other, sees the same.
- Tree-lined roads: Many of Chelmsford's tree-lined roads mean leaves and moss in gutters and valleys, which leads to overflowing gutters and damp patches if it is left. In Shenfield, mature trees fill gutters and valleys too.
- Hidden gutters: Older Wisbech roofs often have parapets, hidden gutters and lead valleys behind the front walls, which can block and leak without being seen from the street.
- Salt air: In Harwich, salty air off the sea rusts metal fixings and gutter brackets faster than inland.
How First4Roofcare can help
We clear, repair, realign and replace gutters and downpipes, and fix the fascias behind them where needed. See our gutter repairs service, or book a free survey and we will find out why yours are overflowing.