Water finds its way through a pitched roof in a handful of ways, and each one leaves its own clues. A tile that has slipped lets rain onto the underlay (the membrane stretched beneath the tiles). A valley, where two slopes run into one another and form a gully, collects the run-off of both and shows up any weakness in its lining. An abutment, the seam between roof and a rising wall or chimney, depends on lead or mortar that has to keep moving with the building. And the underlay itself, out of sight, can fail long before the tiles do.
The aim here is to separate the causes so the right repair is chosen the first time. If your leak comes from a roof laid at too shallow a slope for its tiles, that is a different problem, covered in our guide to tiles on a low-pitched roof. Everything else that sends water through a tiled roof is covered below. For the wider service, see pitched roofing.
Tracing a stain back up the slope
Water does not drop straight down. It runs along the top of the underlay, along rafters (the timbers running from ridge to eaves) and down the face of a chimney breast before it finally drips onto a ceiling. The stain you see can sit a metre or more from the entry point, so the first job on any leak is detective work, not repair.
We start inside, in the loft, armed with a torch, ideally on a dry day. Dark, damp patches on the timbers show the line the water has followed. A wet rafter tends to be wettest nearest the entry point. Daylight through the covering is a clue too, though a pinprick of light in an old roof is not always a leak. From there we go outside and look at what sits directly above the wet area: a tile with a cracked corner, a hip, a flashing, a gutter that has overflowed behind the fascia.
What to note before we arrive
Useful details cost nothing to collect. When did the stain appear: after heavy rain, after a windy night, or only when rain came from one direction? Does it get bigger in a storm and dry out slowly? A leak that only appears with wind-driven rain points to a gap that rain is pushed into sideways, such as a lifted tile or a poor abutment. One that follows any long wet spell points to something saturating slowly, like failed mortar or old underlay.
When the cause is not obvious from the loft or the ground, we survey the slope up close and take photographs of your own roof. You get the prints in the survey report, so the fault is plain to see.
Tiles that have slipped, split or gone
A tile that has slid out of line, cracked or gone altogether is the most visible cause of a leak, and often the simplest to fix. Clay and concrete tiles are hung from battens (the timber laths nailed across the rafters), usually with a nib at the head of each tile. Some tiles are also nailed or clipped. When a nail corrodes, a clip loosens or a batten rots, the tile can creep downwards and leave a gap above it.
The repair depends on how widespread the movement is. One or two slipped tiles can be lifted, re-seated and secured. A cracked tile is replaced with a matching one. MyBuilder's 2026 roof repair guide puts a minor repair at £100 to £300 and notes that repairs generally cost £150 to £1,500, with cost depending on access and extent. A single replacement slate is priced there at £60 to £120. These are third-party national figures. The figure on your quote comes from the survey.
When slipping is a symptom
One slipped tile on a sound roof is a repair. A whole run of slipped or cracked tiles is a message about what lies beneath. If the battens are soft, or the fixings have rusted through across a slope, replacing tiles one at a time becomes a way of spending money on a roof that is on its way out. We tell you if the pattern points that way, and show you the photographs, so you can weigh a repair against a larger job.
Matching matters, too. A replacement should be the same type, size and colour as the tiles around it, particularly on older homes where a modern tile will sit differently on the batten.
Underlay that has perished
Underlay acts as the back-up barrier. Wind-blown rain and snow get under tiles even on a sound roof, and the underlay carries that moisture down to the gutter. When it has torn, rotted at the laps or been pierced by old nails, water that was meant to drain away is free to reach the timbers.
Old bitumen felt can become brittle and split, especially at the eaves and along the ridge where it is stressed. Modern breathable membranes can be damaged during installation or by later work in the loft. A visible tear is one issue, covered in our guide to torn felt seen from the loft; the wider picture of what underlay does and how it ages is in our underlay guide.
Why a small tear can't be patched from above
Underlay sits beneath the battens, and the battens sit beneath the tiles. There is no way to reach it from outside without lifting the covering. A small local tear can be patched from inside the loft, though the remainder of the sheet, probably just as old, stays as it was.
Where the underlay is spent, the honest repair is to strip the tiles, fit new underlay and new battens, and re-lay the sound tiles. That is a bigger job than a leak repair, and we tell you so up front. Re-covering more than half the roof triggers the Building Regulations thresholds set out by the Planning Portal, which we cover in a later section.
Valleys, hips and ridges
A valley is the angle where two roof slopes meet, forming a gully that takes the run-off of both. It is lined with lead, a GRP (glass-reinforced plastic) trough, or in traditional work with specially cut tiles. We cover the types in detail in our guide to tiled roof valleys. For leaks, what matters is that the lining is the one place on a roof where water is concentrated rather than shed.
Common failures are a split in the lead where it has been bent or has fatigued, a lining that has lifted, and moss or leaves that have dammed the gully so that water banks up beneath the tile edges. Debris is often the easiest fix: clearing the valley and checking the lining underneath. A split or lifted lining means cutting back the tiles either side and renewing the lead or the trough.
Ridge and hip tiles
The ridge is the horizontal line at the top where slopes meet, and a hip runs down an outward corner. Ridge and hip tiles were traditionally bedded in mortar. Over time that mortar cracks and falls out, and tiles loosen. BS 5534 was revised in 2014, and under it bedding mortar no longer carries ridge and hip tiles by itself; mechanical fixings are added. On a re-bed we therefore add fixings, or fit a dry-fix system, in which the ridge is held by clips and screws, not mortar and covered by BS 8612 for testing.
In MyBuilder's 2026 figures, re-bedding or swapping ridge tiles costs £300 to £600, while repointing a ridge or hip is £200 to £400, and dry ridge is £40 to £60 per metre. Both are national guides; your figure is set after the survey.
Abutments, flashings and chimneys
Wherever a roof meets something vertical, the junction has to be sealed against water that runs down the wall or the stack. A flashing is a strip of waterproof material, usually lead, dressed over the junction. A soaker is a folded lead tab slipped between tile courses, and stepped flashing follows a sloping wall in a series of steps. Together they form the abutment, and a chimney stack has one on every side.
Lead is durable but it is not permanent. MyJobQuote gives over 80 years for correctly fitted flashing, but lead that has been stretched by heat cycles, split at a corner or lifted by moss will let water in long before then. Cement fillets, sometimes called mortar flashings, crack because the stack and the roof slope shift independently; they are a repeated source of leaks around old chimneys.
Repairs by cause
A lifted section of flashing can be re-dressed and re-fixed. A split in the lead needs patching or replacing, and the lead code (its thickness) must suit the job. Leadworx describes Code 4 as the usual pick for ordinary flashing work. A mortar fillet is replaced with lead, not re-pointed in the hope that it will hold this time.
MyBuilder's 2026 chimney repair guide puts a flashing repair at £250 to £1,200, and MyJobQuote lists a chimney flashing patch at £150 to £250. The stack itself matters too: crumbling pointing or a cracked flaunching (the mortar collar around the pots) can leak into the flue and show as damp on the chimney breast.
Gutters, eaves and the problems that look like roof leaks
Not every wet ceiling starts on the roof slope. A gutter that has overflowed or sagged can send water down behind the fascia into the roof edge. A blocked outlet in a parapet gutter does the same. Check the gutters for plant growth and standing water before assuming the covering has failed. Guttering is normally laid to a slight fall towards the outlet, in the region of 1:600 to 1:350 depending on the system, so a gutter holding water along its length has probably moved.
Condensation that mimics a leak
Dripping from the underside of the roof, or damp patches on rafters and the underlay, can be condensation rather than rain coming in. Warm, moist air from the house rises into a cold loft and condenses on the first cold surface it meets. It is worth ruling this out before paying for roofing work that will not cure it. Our guide to roof ventilation and condensation sets out how to distinguish them and what cures the cause.
Flat-top sections and extensions
A porch, bay or rear extension often has a small flat or lean-to roof joined to the main slope. The junction between the two is another abutment, and the covering of the lower roof has its own lifespan. If the stain appears below one of these, it is worth surveying both roofs rather than only the tiled one.
If a repair is the answer, we deal with safety before anything else, and leaks and storm damage get priority.
Repair or replace, and the paperwork that follows
Many leaks end with a localised repair: tiles reset, a valley lining renewed, a flashing re-dressed. The test for a repair is whether the surrounding roof is sound enough to carry on. If battens are rotten, the underlay has perished or the tiles themselves are crumbling, a repair buys time but not a result.
Full re-roofs run from about £5,000 to £12,000 in MyBuilder's 2026 figures, and scaffold alone is about £1,125. A job of that size calls for a written quote that covers scaffold, the strip, materials, labour and clearance. We also explain what a partial re-cover means for the rest of the roof.
When Building Regulations apply
The Planning Portal says a building control application is not normally needed when under 25 per cent of the building envelope and under 50 per cent of the roof is affected. Approval is needed for a covering that adds 15 per cent or more to the weight, or whose fire performance is significantly different. Any consent is explained up front, and for notifiable work the Building Regulations paperwork is ours to handle. For a listed home, or one inside a conservation area, ask Stroud District Council's planning team before work starts; our guide on clay-tiled roofs on protected homes is a good place to begin.
Whatever the scale, we leave the site clear, remove the waste, and put our 10-year workmanship guarantee on paper.