The short answer
A small valley repair such as clearing debris and refixing a few tiles usually sits in the minor band that MyBuilder prices at £100 to £300. Relining a valley with new lead or a GRP trough is a bigger job, often moderate to major, and on a two-storey house scaffolding of around £850 to £1,200 can be the largest single cost.
What a roof valley is, and why it fails
Picture the inside corner where a rear extension roof runs into the main roof: that crease is a valley. Rain from two slopes funnels into one narrow channel there, so the lining takes far more water per metre than the slates or tiles around it. Valleys are lined with lead on older roofs, with preformed GRP or plastic troughs on many newer ones, and some tiled roofs use special valley tiles.
They fail in a handful of ways. Debris builds up and water spills over the edge of the lining. Lead cracks at laps and bends, or thins with age. GRP troughs crack or lift at their edges. The mortar bedding the cut slates or tiles along each side perishes, and the tiles slip. Our guide to the most common causes of roof leaks puts valleys in context with the other usual suspects.
Typical costs by type of repair
A valley repair is priced on survey, because the work ranges from a short visit to a partial strip of the roof. The bands below come from MyBuilder's roof repair guide, updated in August 2026, and Checkatrade's October 2026 repair guide, and show where valley work tends to fall.
| Job | Typical national range |
|---|---|
| Clear a blocked valley, refix a few slates or tiles | £100 to £300 (minor repair) |
| Re-bed cut tiles along a valley, patch a lead joint | £500 to £1,000 (moderate repair) |
| Strip both sides, new lead or GRP valley, relay | £2,500 or more (major repair) |
| Scaffolding for a two-storey house | £850 to £1,200 |
These are typical figures across the UK, not prices for your roof. A written quote after someone has looked at the valley is the only figure worth planning around.
What moves the price up or down
Access is the first factor. A valley on a single-storey extension can often be reached from a ladder or a small tower; one between two slopes on a three-storey Victorian house needs a scaffold, and the scaffold may cost more than the valley work itself.
The lining comes next. Relining with lead means cutting and dressing new sheet, usually Code 4 or 5, with laps long enough to stop water running back. A GRP trough is quicker to fit and suits many tiled roofs. Listed buildings and conservation areas usually call for lead.
Then there is the covering either side. To replace a valley lining, the slates or tiles along both edges have to come off and go back on, and some will break. Natural slate and handmade clay tiles cost more to replace than modern concrete tiles. Rotten boards or battens under the valley add to the job, and you only find them when the old lining comes out.
Repair or replace the valley?
If the lining is sound and the problem is debris, a cracked joint or a few slipped tiles, a repair is the sensible answer. If the lead has cracked in several places, has worn thin, or was laid with laps too short to keep water out, patching one crack usually just moves the leak along. That is the point to reline the whole valley.
GRP troughs that have cracked are normally replaced rather than patched, since a repair on a cracked trough rarely lasts. Whichever route you choose, ask to see photographs of the valley before you agree, so you know what you are paying for. A good photo shows the full length of the valley, the lead or trough itself, and the tiles along each edge. Our page on whether roof repairs are worth it covers the same question for the roof as a whole.
Where valleys sit on Swindon houses
On the Victorian and Edwardian terraces around the town centre, valleys usually appear where a back addition, the narrower rear wing that holds the kitchen and bathroom, meets the main roof. They are often lead, often old, and sometimes shared with the house next door, so a fault on one side can soak the other.
On larger villas in Old Town and on hipped bungalows, valleys form wherever the roof turns a corner. Post-war and modern estates have fewer valleys, but extensions and porches added later often create new ones, sometimes with a plastic trough laid in a hurry. Dormer roofs bring their own small valleys and soakers where the dormer cheeks meet the main slope.
Knowing where your valleys are helps you check them: look for them from the garden after heavy rain, and in the loft for damp timber directly underneath.
Keeping a valley working
Most valley trouble starts with blockage. Leaves, moss and twigs collect in the channel, water backs up, and the overflow finds its way under the slates. Clearing the valleys once or twice a year, especially after leaf fall, prevents a lot of repairs. Trimming branches that overhang the roof helps too, and so does a quick look from the garden after any big storm.
Please do not climb onto the roof to do this yourself. A roofer can clear valleys and gutters on the same visit, and check the lining while they are up there. If you suspect a valley is already letting water in, our roof repairs team will trace it and price the fix in writing.