Roofs rarely fail in one dramatic moment. They decline in stages, and the early stages look a lot like an ordinary repair job: a slipped tile, a damp patch that appears in a gale and dries by the weekend. The difficulty is knowing when a run of small faults has become one large one. This guide lists the signs that point to the end of a roof's life, and sets each beside the lookalike that only needs mending. Some can be spotted from the garden with binoculars. Others show in the loft, where the underside of the covering tells a plainer story than the top. None of this replaces an inspection on the roof itself, but it should help you describe what you have seen, and recognise when a conversation about a new roof is worth having.
Slipping and loose coverings across several slopes
One slipped slate is a repair. A scattering of them across a whole roof is a symptom. The distinction is where they are and why they moved.
Slates and clay tiles are hung on battens, the timber laths fixed across the rafters. Slates are held by two nails each, and those nails are the weak point. Over many years the iron corrodes in damp air until the head or shank gives way, and the slate drops a few centimetres or slides out altogether. When this is the cause, slipping is not random. It tends to start on the most exposed slope and to spread, because the nails there were all fitted at the same time and have all aged at the same rate.
From the ground, look for slates that sit out of line with their neighbours, for dark gaps in the courses, and for fragments in the gutters or on a flat roof below. Look at the ridge too. A ridge line that has dipped, or ridge tiles that have shifted, shows the bedding has failed along its length, which is a larger job than replacing one piece.
On concrete and clay tiles, the fixings are different. Plain tiles hang from nibs and are held by clips or nails at intervals, while interlocking tiles are clipped at the edges. The warning here is lifted tiles along the gable verge and low down at the eaves after a gale. If the same places keep being disturbed, the cause is often a fixing that has failed, not bad luck.
The test we apply is simple. We lift slates or tiles at several points and examine the nails and battens underneath. If the fixings are sound, we repair. If they are rusted through in several places, a new roof is the honest answer and patching only buys a season. Our page on repairing or replacing a roof works through that decision.
A perished underlay and what the loft shows
The loft is the best place to judge a roof, because it shows the back of everything. Go up on a dry day with a torch and study the underside of the roof before you look anywhere else.
The layer beneath the battens, laid over the rafters, is the underlay. It exists to intercept rain driven under the covering, along with condensation, and let both drain off. Older houses may have a stiff bitumen felt that has cracked, or no underlay at all, with the tiles or slates bedded straight onto lime hair-mortar called torching. Where felt has split or sagged between the rafters, water runs into the loft along the line of the tear. Where there is no underlay, daylight shows between the slates and fine dust or snow can blow in during winter.
What to look for is a short list. Daylight through the covering other than at a deliberate vent is one sign. Dark tide marks or damp patches on the rafters, felt hanging in folds, and the smell of damp timber are others. Nail points that have rusted and are shedding orange flakes on the underside of the battens show that moisture has been sitting there for years. So does white or green mould on the timber.
If these appear across more than one slope, the underlay has failed as a system, and a replacement means stripping the covering so that new underlay and battens can be fitted. That is the essence of a re-roof, and it is why a roof with a failed membrane cannot be put right from the top by adding tiles.
Condensation is the lookalike. Staining that sits in the colder corners of the loft, without any trail from the roof above, can come from warm air rising from the house and meeting cold timber. That points to ventilation and insulation, not necessarily to a new roof.
Sagging, dips and distortion
A roof should read as flat planes meeting at straight lines. When the planes bow or the lines wander, something underneath is moving.
Stand at the far side of the road and look along the ridge and across each slope. A dip in the ridge suggests a rafter pair, a purlin (the horizontal beam supporting the rafters at mid-span) or a ridge board is under strain. A slope that belly outwards between the ridge and the eaves can mean the rafters are spreading, or that the battens have rotted and the covering has lost its support. A bulge at the eaves can come from the wall plate, the timber at the head of the wall, having decayed where water has been running into it.
Distortion is a different category from a loose tile, because the cause is structural. Replacing the covering does not cure a sagging rafter. The roof has to be opened, the timber assessed, and repairs made before the new covering goes on. In some cases a short length of rafter is doubled up alongside the old one, or a section of wall plate is replaced. In others the movement is old and has stopped, and it only needs to be understood.
Take care with interpretation. Old houses are rarely true, and a handmade clay or stone-tiled roof has an irregular, undulating surface that is part of its character. Waves can be sound, which is why we compare what we see with the line of the ridge and eaves and with what the loft shows. A slope that has changed shape within your memory matters more than one that was always uneven.
If you see a new dip, new cracking in the ceiling below it, or doors and windows beginning to stick beneath a roof, ask for an inspection promptly rather than waiting for the next wet spell.
Leaks that return in different places
A leak is not in itself a sign that the roof is finished. Most leaks have a local cause and a local cure. What marks the end of life is the pattern.
Compare these two situations. In the first, a stain appears below a chimney during heavy rain, the lead flashing around the stack is found to have lifted, and once it is redressed the ceiling stays dry. The roof is sound and the fault was in one detail. In the second, a damp mark appears in the back bedroom one winter, is traced to a slipped slate and fixed, then another appears over the stairs the next winter, and a third in a different room the winter after. Each repair was correct and each leak was real, but together they show a roof that is failing in more places than a roofer can chase.
| What you see | Usually means |
|---|---|
| Stain below a chimney in driving rain | A lifted flashing: a repair |
| Different room stained each winter | Wider failure of covering or underlay |
| Drip along a valley or parapet gutter | Lead split or thinned: relining or repair |
| Stains in the cold corners only | Condensation: ventilation and insulation |
Keep a simple record. Note the date, the weather, the room and the position of each stain. A roof leaking only in driving rain from one direction points to a flashing or an exposed edge. One that drips in any prolonged wet points to the covering or underlay across a wider area. Leaks around valleys and parapet gutters, the lead-lined channels that carry water off between slopes and behind walls, belong to a third group. Lead that has split at a joint or cracked at a fold can be repaired, but lead that has been patched repeatedly and has thinned and creased across its length is often better relined.
Also read the ceiling below. A new brown stain with a tide line, plaster that bubbles or flakes, and paint that blisters without any plumbing above are all moisture arriving from the roof. If the stains are in several rooms, speak to a roofer before the timber is affected.
Surface decay: tiles and slates that are wearing out
The covering itself ages, and its failure is visible if you know what to look for. Each material wears in its own way.
Natural slate
Good slate stays hard and rings when tapped. Poor or tired slate delaminates, meaning it splits into thin layers from the tail upwards, and goes soft and powdery at the exposed corners. Some slates carry iron inclusions that rust and leave orange streaks. If many slates across a slope show flaking edges, the supply of sound slate to reuse is limited, and a re-slate with matching new or reclaimed slate is the sensible course.
Clay tiles
Clay is durable, but it can be damaged by frost. Water absorbed into the body of a tile freezes and flakes off the surface in a process called spalling. A tile that has lost its glaze or face and shows a rough, pale underside is nearing the end. Clay tiles that are sound can often be sorted and reused when the roof is stripped.
Concrete tiles
Concrete tiles lose their surface coating over time, which exposes the cement and sand beneath and makes the colour fade and the texture grainy. This is not harmful in itself, though a heavily eroded tile absorbs more water and becomes heavier. A crack straight across a tile, as opposed to chipped edges, hints at foot traffic or poor ageing.
Stone tiles
Natural stone tiles may laminate in the same way as slate, with the faces flaking off. Because stone tiles are heavy and sit on substantial timbers, their replacement is a specialist job, and an assessment should always include the roof structure.
Surface wear alone seldom decides the question. It matters when it is widespread and it coincides with the other signs. When replacement is the decision, our guide to materials for a new roof compares what can go back on.
Signs that look worse than they are
Not every warning is one. A fair account of the evidence includes the things that alarm people without justifying a new roof.
Moss and lichen are the commonest. They look neglected and can hold moisture against the surface, and heavy growth can block gutters and lift the edges of tiles. But a mossy roof can be perfectly sound under the green. Removing moss is a cleaning job, and it is worth knowing that some cleaning methods can damage delicate tiles. Growth is a reason to look more closely, not a verdict.
An old stain on a ceiling with no sign of recent damp is often the record of a leak that was mended years ago. Check it with a damp meter, not just by eye, and see whether it changes after rain. A single missing tile after a storm is usually the cheapest fault in the book. Leaning on a chimney that has pulled away from its flashing is similar: the fix is local, and it belongs with the chimney work, not the roof as a whole.
Rising energy bills are sometimes listed as a sign. They can be, but they depend on insulation and heating more than on the covering, and a new roof is not the first remedy for a cold house. The same goes for noise in the wind: a rattling tile or loose ridge can be fixed without replacing anything.
The other category is the roof that is old but working. Age is not a defect. A roof laid with sound materials and well fixed can keep going long after it has passed an age at which you might expect it to fail. We look at how long different coverings tend to last in our page on how long a roof lasts.
What to do once you have seen the signs
If you have recognised two or three of these signs together, the next step is an inspection, not a decision. A roofer needs to go up and inside, because the cause decides the answer. We survey for free, we photograph your own roof so the evidence is yours to see, and we put the findings in writing. If a repair will hold, we will say that and price it. If the roof is at the end, you receive a fixed price for replacing it.
It can help to know what the alternatives are before the visit. A new covering laid directly over the old one, called an overlay, is sometimes proposed on cost grounds, and we explain when it does and does not make sense in our answer on roof overlays. On a listed house the covering becomes a consent matter too, and listed building consent has to come from B&NES Council. The World Heritage Site is the whole of Bath, whereas its conservation area is roughly half.
For safety, do not climb onto a roof to inspect it, and be careful on a loft ladder. Binoculars from the ground and a torch from the hatch show a great deal. Note anything you see, take dated photographs, and keep a record of when stains appeared.
Our roof replacement work aims to leave the roof matching what was there before. If you are unsure whether the signs add up to replacement, photograph them from the garden every few months so any change is easy to compare.