Roof valley leaks & repairs
In short
A valley carries the water off two roof slopes at once, so when it fails the volume is significant and the damage is quick. Most valley leaks come down to a split in the lead, a valley that is too narrow for the water it takes, or one packed with moss and debris.
Also called: Valley gutter leaking · Lead valley · Roof valley repair · Blocked valley
Signs you need this
- Damp on a ceiling or wall directly below where two roof slopes meet
- Visible splits, cracks or holes in the lead of a valley
- A valley packed with moss, leaves or mortar debris
- Water only coming in during very heavy rain
- Mortar filling or cement 'repairs' along the sides of a valley
- Bituminous paint or tape over a valley lining
A valley is the internal angle where two roof slopes meet, and it is the busiest square metre of any roof. Everything that lands on both slopes funnels into it, which is why a valley failure floods rather than drips, and why it damages structure faster than almost any other defect.
Traditional valleys are lead-lined, and lead fails in predictable ways. It splits where it has been laid in pieces that are too long — lead moves a great deal with temperature and a valley run as one continuous strip will fatigue and crack, always across the middle. It fails where it has been dressed too thin over a sharp arris. And it wears through at the bottom end where decades of grit-laden water have scoured it.
Then there is capacity. Valleys on Victorian roofs were sized for the roof as built. Add a rear extension whose slope discharges into the same valley, and it may simply be too narrow for what now runs down it — so in heavy rain the water backs up above the level of the slate laps at the sides and goes in sideways. That leak only ever appears in a real downpour, which makes it maddening to diagnose and obvious once you know.
Blockage is the other big one and it is preventable. Moss shed off the slopes, leaves off an overhanging tree, and mortar debris from a ridge or a chimney all collect in the valley because that is where everything goes. A packed valley holds water permanently against the lead and against the slate laps either side. Clearing valleys is part of ordinary maintenance and it is a fraction of the cost of the damage it prevents.
Mortar in a valley is a warning sign. Some older valleys were 'repaired' by filling the sides with mortar or by cementing the slates in, which restricts the channel further and cracks within a couple of frost cycles. Bituminous paint over a lead valley is the same story — it hides the split for a season and holds water against the metal underneath.
Replacement is a bigger job than it sounds because the slates or tiles either side have to come off to get at the lining. Done properly it means new lead of the right code, laid in appropriate lengths with proper laps and a tilt fillet, on a sound valley board, with the coverings cut and re-laid cleanly to the correct margin either side. GRP and fibre-based valley liners are also used and can be a sound answer, particularly where the geometry is awkward.
What the job covers
- Valley cleared and inspected along its full length
- Lead assessed for splits, fatigue and thinning
- Capacity checked against what actually drains into it
- New lead of the correct code, in properly lapped lengths
- Valley boards and any rotted timber beneath replaced
- Slates or tiles cut and re-laid to a clean, correct margin
What it costs
We don't publish a price for this yet, because a number pulled out of the air is worse than no number at all — your roofer has to honour it. On roofing it would also be close to meaningless: access is often the biggest single factor, and it varies enormously house to house. You'll get a firm price for your actual job when they ring you back, before any work starts. The quote itself is free and there's no obligation either way.
Common questions
Can a split valley just be patched?
Small, isolated damage can be patched properly with lead-welded repair, and that is a legitimate fix. What is not a fix is tape, bituminous paint or sealant over a split — those hold water against the lead, hide the crack, and make the eventual replacement worse. If the lead is fatigued along its length, patching one crack simply moves the failure a foot along.
Why does it only leak in heavy rain?
That is the signature of an undersized or partly blocked valley. In normal rain the water runs down the channel; in a downpour it backs up above the level of the slate laps either side and goes in sideways. The commonest cause is an extension that now discharges into a valley built for a smaller roof.
How often should a valley be cleared?
Annually if there are trees over the roof or much moss on the slopes, every two or three years otherwise. It is a cheap job that prevents an expensive one, and it is the single most useful bit of maintenance on any roof with valleys in it.
How long should a lead valley last?
Correctly specified lead, laid in the right lengths with proper laps, will do many decades — often the life of the covering. Lead laid as one long continuous strip fails far sooner, usually within ten to fifteen years, because thermal movement fatigues it. If yours has failed early, that is normally why.
Need this doing in Macclesfield?
Tell us the job and it goes straight to our local roofer — one call back, usually the same day. Free quote, no obligation.