Six faults found on British pitched and flat roofs, with the usual cause of each, what a lasting fix involves, and why the cause is always mended before the stain is touched.
Roof faults tend to go by a few familiar names: a slate that has slid, a flashing that has lifted, a ridge that has cracked, a gutter that has filled, a flat roof that has split. They are common because every roof meets the same enemies, which are water, wind, frost and time, and each fault sits at a place where one material has to join another.
A ceiling stain is only the end of the story. Rain that gets past the covering travels along the timbers before it falls, so the mark inside can sit metres from the hole. A repair that deals with the stain, or with the first thing that looks wrong, often leaves the real fault in place. The rule on every one of these problems is the same: find the cause, mend that, and only then make good the damage.
This guide covers British coverings only: slate, clay and concrete tile, lead, felt, rubber and fibreglass. Each section names the covering a fault affects and the repair that puts it right. For urgent trouble, our roof repairs and emergency page shows how to reach us.
Slipped, cracked and missing slates and tiles
This fault can announce itself with a piece landing in the garden. A slate is held by nails driven into the batten beneath, or by a clip, and a tile hangs from a nib or a nail. When the fixing rusts or the batten weakens, the slate slides down and leaves a gap. A cracked piece may keep out rain for months, then let go in a frost.
The fix is to lift the course above and replace the broken piece with a matching one, fixed properly. A repair that relies on sealant alone is a delay, not a repair. If many pieces are loose across one slope, the problem is the fixings and not the individual slates, and spot repairs will keep returning.
For typical UK costs, Which? Trusted Traders put £75 to £400 ex VAT on putting back one to six missing or cracked standard tiles, from a survey gathered in November 2025. Which? warns that its scale tops out for London and South East jobs, Kent being part of the South East. The price of your own repair is written after a survey, once somebody has seen how many pieces are loose and how hard the roof is to reach.
- One or two loose pieces on an otherwise sound slope: a local repair.
- A line of slipped slates in the same course: look for a split batten or failed nails behind them.
- Slipping across the whole slope: ask for a view on how long the fixings have left.
Our page on cracked roof tile repair goes through the steps.
Flashings, valleys and chimney joints
At every joint between roof and wall or chimney, a flashing seals the joint. It is normally lead, bent to the shape of the junction. Soakers, small folded pieces of lead slipped under each course of slates or tiles beside the wall, work with the flashing to carry water over the joint and onto the roof. When lead cracks, lifts or is smeared with a gunge of mastic, rain finds a way behind it.
A valley is where two slopes run together into one channel, so it carries the runoff of both. Leaves collect in it, and its lining wears. Leaks here can look like a fault in the middle of the ceiling, far from the wall.
Lead codes and chimney joints
Lead comes in thickness codes. Code 3 is the one for soakers, while the code for each other detail comes from the job's specification, so ask any quote to name the code it uses. Fixing a chimney joint properly means cutting the lead into the mortar joint, dressing it down and sealing it, not smearing a line of mastic.
MyJobQuote's guides give typical UK ranges of between £350 and £920 for chimney leadwork and around £540 for a valley. They are national averages, not Castle prices. Flaunching, the mortar bed on top of the stack, is also part of this junction story, since a cracked bed lets rain reach the brickwork.
See finding the source of a roof leak for how a roofer traces water back to a flashing.
Cracked ridge and hip mortar
Along the crest of a pitched roof runs the ridge, and the hips are the sloping lines that run down to the eaves from it. The tiles that cap them have traditionally been bedded in mortar. Mortar cracks as the roof moves and weathers, and once the bed fails, a ridge tile can rock or fall. Crumbs of mortar in the gutter, or a visible gap under the capping when you look through binoculars, are early clues.
Standards have shifted. Marley notes that after the 2015 amendments to BS 5534, mortar by itself no longer suffices to hold the covering on, and BS 8612:2018 is the standard for fixing ridge, hip and verge pieces dry. Mortar remains in use on ridges; what changed is that it should not be the only thing keeping the tiles down. A repair today may pair a mechanical fixing with a mortar bed, or use a dry-fix system, which holds the capping with clips and screws.
The verge, where the slope finishes beside a gable wall, is treated with equal care. A dry verge system replaces the mortar that once sealed the ends of the tiles, and the MyJobQuote figure below covers fitting one.
| Item | Figure | Source |
|---|---|---|
| New ridge tile | £80 to £300 ex VAT | Which? |
| Ridge tiles | £225 to £550 | MyJobQuote |
| Dry verge system | £500 to £2,000 | MyJobQuote |
Those figures come from a Which? survey of November 2025 and MyJobQuote pages from October 2026. What your ridge costs depends on its length, how easily it is reached and the state of the bed, and the written price comes after a survey.
Blocked, leaking and sagging gutters
Gutters rarely get attention until they overflow. A blocked outlet sends water over the front edge or down the wall, where it soaks brickwork and can reach the fascia, the board carrying the gutter, and the soffit under the eaves. Over time that causes damp patches inside, rot in the roofline timbers and green staining on the wall.
The causes are leaves, silt, moss washed down from the roof and plain neglect. Joints leak when the seal perishes, and a gutter sags when brackets rust or the fascia behind has gone soft. A gutter needs a slight slope to its outlet: Brett Martin suggests 1 mm for every 600 mm, so a dip that holds standing water is a fault in the fall.
- Overflow in rain from the middle of a run points to a blocked outlet or a sagging section.
- Dripping at a joint means a failed seal, which can be refitted.
- A gutter pulling away from the wall needs new brackets, and perhaps a sound fascia to fix them to.
On cost, Which? gave a typical UK range of £75 to £350 ex VAT to clear all the gutters on a property, while MyJobQuote gave around £1,000 to £1,600 for a replacement. Neither is a Castle price, and both are national figures. Gutters over a footpath or on a neighbour's side need care, and work at height from a ladder should be left to those equipped for it. A gutter that keeps filling after a clear-out usually has a cause upstream, such as moss shedding from the slope above.
Split, blistered and ponding flat roofs
Flat roofs are not flat: a good one has a slight fall towards the outlet. They fail by splitting along a seam, blistering where moisture is trapped, or holding water in a dip. Edges and upstands, the short vertical faces where the covering climbs a wall, are the weak points.
Published lifespans vary. HomeBuilding gives felt 10 to 15 years and Less 10 to 20. For EPDM, a rubber single-ply membrane, HomeBuilding says 25 to 30 and Less says 30 to 50. For GRP, glass-reinforced plastic, the ranges are 25 to 30 and 25 to 40. A flat roof at the end of its range that is leaking in several places is a replacement conversation, and one with a single split may only need a local repair.
Water that stands a day after rain suggests the fall is wrong. BS 6229:2025 covers membrane roofs and the minimum finished fall is read as 1:80; IKO advises a design fall of 1:40 for single-ply roofs. Lead roofs follow BS 6915 through Approved Document C and not BS 6229.
- Look at the surface for blisters, splits and bare patches.
- Check the outlets for debris and the edges for lifting.
- Look at the ceiling below for stains that follow rain.
Checkatrade's June 2026 repair guide gives EPDM rubber repairs at £120 to £170 per m². Its rates apply only to repairs of up to 3m² and are exclusive of VAT, so they are never a basis for pricing a whole roof.
Damp, condensation and the cause behind the stain
Not every wet patch is a leak. Warm, moist air from kitchens and bathrooms condenses on cold surfaces in a loft with little ventilation, and the drips can mimic a hole. BS 5250:2021 is the current standard on managing moisture in buildings, and a roof that lacks air movement can grow mould on the timbers long before a tile fails. Our answer on condensation or roof leak helps you tell the two apart.
The general discipline is the same as for every fault above. Trace the water to its entry point, fix that, then dry out and redecorate. A roofer who offers to seal a stain, or to coat the roof without looking at what is under it, is treating the symptom.
| Problem | Usual cause | Lasting fix |
|---|---|---|
| Slipped slate | Rusted nail, split batten | Replace piece, refix |
| Lifted flashing | Cracked lead, failed seal | Renew in lead |
| Loose ridge | Cracked mortar bed | Rebed or dry-fix |
| Overflowing gutter | Blocked outlet, bad fall | Clear, reset, reseal |
| Ponding flat roof | Fall, worn membrane | Repair or recover |
A good repair ends with photographs of what was found and a total written price that the roofer gives after the survey, so you can see what you are paying for before work starts. If the roofer cannot show you where the water got in, ask for the survey to carry on until they can, because a repair made without that answer is a guess. Keep the photographs with the paperwork, since the same page of the roof may need attention again in years to come and the photographs prove what was done.
