Roofs fail in familiar places. The covering shifts, the joints between roof and wall open, the mortar that holds the top edge in place crumbles, and the gutters that carry water away clog or sag. A roofer who climbs up to a house in Stroud, Nailsworth or Painswick is mostly looking at one of six things, and the list barely changes between a Victorian terrace and a 1970s semi.
This guide runs through those six repairs in the order they tend to turn up: loose tiles and slates, ridge and verge mortar, flashings, valleys, flat roof splits and guttering. For each we explain what failed, why, and what the fix involves. What damages roofs in the first place is a separate subject, covered in our guide to what damages roofs the most. Prices for these jobs are in the national ranges on our roof repairs page.
Slipped, cracked and missing tiles and slates
The commonest call is a tile or slate that has moved. Clay and concrete tiles hang from timber battens by a nib on the back, and many are also held by a clip or a nail. Natural slates are nailed or hooked. Stone slates, of the kind on older Cotswold-edge cottages, hang on wooden pegs. In every case the fixing is the weak point, not the covering.
Why they move
Nails rust, pegs rot and battens soften where damp has sat for years. Wind then lifts a tile a fraction at a time until it slides, or rain gets under a slate that has dropped a few millimetres and the rest of the course follows. Frost can split a porous tile. Boots are another cause. Old slates crack under anyone who walks across them to reach an aerial, a chimney pot or a blocked gutter.
The fix
Replacing one piece is simple when the neighbours are sound. A tile is lifted clear, the batten checked and the new piece fixed with a clip, or a slate is held with a tingle, a small strip of metal that clips the tail of the slate in place. Matching matters. A tile from a different batch will not sit in the same colour or camber, so we match size, thickness and age where we can. On a stone roof, the replacement is chosen from the same band of slate lengths so the courses keep their lines.
That is the point to stop patching. When fixings and battens are failing across an area, the honest repair is a strip and re-lay of that area, not a tile at a time.
Ridge and verge mortar
The ridge runs along the apex, capped by ridge tiles, with a slope falling away on each side. At a gable end, the covering finishes against the wall head; that rake of the roof is the verge. On most pitched roofs built before about the 1990s, both were finished in mortar: ridge tiles bedded on it, and the verge tiles or slates sealed to the wall head with it.
Why mortar fails
Mortar is rigid, and roofs are not. Timber moves with moisture and temperature, and the mortar gradually cracks, shrinks away and lets rain in. Once it has crumbled, ridge tiles can rock loose and fall. Birds pick at the gaps and moss grows in them. The failure is slow and easy to miss from the ground. A gust that moves a half-loose ridge tile is often the first anyone knows of it.
What the standard says
Under BS 5534:2014, ridge, hip and verge pieces are mechanically fixed, with mortar no longer trusted to do the holding alone. Marley, the tile maker, describes the 2014 revision as making clear that mortar's tensile strength could no longer be depended on. Dry-fix systems, tested to BS 8612, hold the ridge and verge with clips and fixings and do away with most of the mortar.
The repair
A repair can mean raking out failed bedding and re-bedding the ridge with new mortar and mechanical fixings, or stripping the ridge and fitting a dry-fix system. Re-pointing the verge, or re-bedding verge tiles, is the same kind of job. Either way, the mortar underneath the ridge pieces, called flaunching where it caps a chimney pot, is checked for the same shrinkage. The work needs a safe position at the top of the roof, usually a scaffold tower, because a ladder at the ridge offers no secure place to work.
Flashings: where roof meets wall and chimney
Flashing means a strip of metal, normally lead, dressed over the junction between the roof and anything upright: a chimney, a parapet, a dormer cheek, the house next door. Lead is the normal choice because it can be shaped to the junction and lasts. MyJobQuote's guide says correctly installed lead flashing can outlast 80 years, and heavier codes longer still.
What goes wrong
The metal itself rarely fails first. Its fixings do. Lead is tucked into a cut groove, or chase, in the brickwork, and held there with lead wedges and pointing. When the pointing falls out, the top edge lifts, and water runs behind it. Poorly made flashings fail earlier, especially where the lead was laid in lengths too long to allow for expansion. MyJobQuote advises 1.5 metre lengths for lead. Cement fillets, a hard mortar slope used in place of a flashing, crack and let go within a few years.
Steps and soakers
Along a sloping wall the flashing is stepped to follow the courses of the brick, and on a tiled roof small pieces of lead called soakers sit under each course of tiles and turn up the wall. These are hidden, and when a roof is re-tiled it is worth checking they are still intact. Tiled roofs with rotted soakers leak at the wall junction even if the flashing above looks sound.
Lead comes in numbered codes by thickness. Leadworx calls Code 4 the standard choice for general flashing, with Code 5 the step up for heavier duty.
A chimney is the most frequent flashing repair. It has four sides, and each needs its own detail: a back gutter behind the stack, aprons at the front, and step flashings on the sides. We inspect all four from the roof, or by drone photographs where the access is awkward.
Valleys: the gutter at the meeting of two slopes
A valley forms wherever two slopes meet at a re-entrant corner and share their run-off. Everything that falls on both slopes runs down it, which makes it the most heavily worked line on the roof.
Three kinds of valley
One kind is a gutter lined with lead sheet, with tiles or slates cut to sit alongside it. A concealed or swept valley, traditional on Cotswold stone roofs, curves the courses of stone round the corner with no visible metal. A modern valley may use GRP or plastic valley trough sections. Cotswold District Council's guidance on stone slate roofs describes the swept version as built from specially cut slates, and calls close-mitred and open lead valleys cheaper but less satisfactory.
Causes of failure
Valleys block with leaves, moss and silt, and water backs up and runs under the covering at the sides. Lead cracks where it has been walked on, or where a poor lap has been stretched. Cut tiles along the valley edge are smaller and more likely to crack or slip. In a swept stone valley, a displaced skew can open a path for water straight to the timber below.
Repairing a valley
Clearing the debris is the first step and sometimes the whole fix. After that, the repair depends on the lining: patch or replace a cracked section of lead, re-lay displaced cut slates, or renew a failed trough. The work is more involved than a tile swap, because the courses either side of the valley have to be lifted to reach the lining, then re-laid and made to match. A leak at a valley often shows inside as a stain in the ceiling well below the actual fault, as the leak tracing guide explains in how roofers trace a roof leak.
Flat roof splits, blisters and ponding
Flat roofs on extensions, garages, porches and dormers produce their own set of repairs. They are not flat, in fact. BS 6229 calls for a design fall of 1:40, giving a finished fall of 1:80, according to Rockwool and IKO. Weak decks and ageing roofs sag, though, and water settles in the dips.
The usual faults
On built-up felt, the surface cracks as it ages and the layers lift in blisters. With EPDM, a rubber sheet laid whole, trouble starts at the seams and edge trims. GRP, which is glass-reinforced plastic or fibreglass, can crack along the board joints where the deck moves, or where a roof has been walked on heavily. Penetrations such as a rooflight kerb or a vent pipe collar are a third group.
Lifespans and what they mean
Published lifespans vary widely. MyBuilder gives 15 to 30 years for flat roofs generally; Less gives 10 to 20 years for built-up felt, noting a poor job might fail in under 10, and 25 to 40 years for GRP; GreenSpec gives 20 to 30 years for EPDM. Those are ranges, depending on workmanship and care, and no promise.
What repair can do
A split, a blister or a failed seam can be cut out and patched. Ponding is harder. Standing water speeds the ageing of any membrane, and a repair that leaves the dip in place only postpones the next failure. If the deck itself has gone soft, the answer is a new deck and covering, which is replacement rather than repair. Photographs taken during the survey mark the damp areas, so the decision rests on what you can see.
Gutters, downpipes and fascias
Gutters are not strictly part of the roof, but a roofer is called for them as often as for anything above. They sit at the bottom edge of every slope, and when they fail water is thrown against the wall, the fascia board or the eaves timbers.
What fails
Leaves, moss and silt fill a gutter until it overflows. Joints in older sections open as the seals harden. Brackets pull away from a rotten fascia and the run sags, so water pools instead of draining to the outlet. Makers of guttering ask for a gentle fall to the outlet, roughly 1:600 to 1:350 depending on the system, with brackets at set spacings. A sagging run breaks both rules and holds water.
The fascia behind it
Behind the gutter, the fascia board carries the brackets. Years of wetting soften it until screws no longer bite. If the board is soft, we flag it at the survey, because a new run bolted to rotten timber will soon sag again. Soffits, the boards under the overhang, can hide the same trouble from view.
Repair or replace
Clearing and re-sealing is a modest job. Re-hanging a run on new brackets, or replacing a cracked section, is next. Where the sections are brittle and joints repeatedly leak, a full replacement is more sensible, and it is often done alongside fascia work, so the access is set up only one time.
Sound repairs of any of these six kinds carry our written 10-year workmanship guarantee. When the cause of a stain is not obvious, our guide to what to do when a roof is leaking covers the first steps indoors.