A roof rarely fails all at once. It declines in stages, and the early stages look like small jobs: a tile on the path, a stain on the landing ceiling, a patch of moss that keeps coming back. Each can be fixed on its own. The question is whether they are separate faults or one fault showing up in several places.
This guide lists the symptoms that, taken together, suggest the covering or its supporting layers are near the end of their working life. It describes what you can see, from the garden or from inside the loft, and what a proper survey adds. It does not explain why roofs fail; our page on why roofs fail covers the causes. For the whole job once you have decided, start at roof replacement.
Slips and cracks that spread across the slope
Every roof loses the odd tile or slate, especially after a storm. What matters is the pattern. A single slip near a chimney is a local fault. Slips that appear here, then over there, then back where you thought you had fixed them, suggest the fixings across the whole slope are tiring.
Look from the ground, ideally with binoculars, on a day when the light rakes across the roof. You are looking for slates or tiles sitting lower than their neighbours, gaps in the rows, broken corners and pieces on the lawn or in the gutter. On natural slate, the cause is often nail fatigue: the iron nails holding each slate corrode and let go, so the slates hang by little or nothing. Repairing one at a time with a copper tingle (a strip of metal that clips a slipped slate back in place) is reasonable while the problem is local. When the next slate beside it is loose, and the next, the repair bill is a fund for the new roof.
Cracked and flaking surfaces
Tiles can also crack across the face, flake at the edges or lose their surface layer. Slate can split along its grain and shed thin sheets, a fault called delamination. A few are normal. Large areas of it are not.
MyBuilder, in a guide updated in August 2026, puts a single slate repair at £60 to £120, and five to ten slates at £150 to £350. That is sensible money for an isolated fault. It stops being sensible when the same job comes round every winter.
What the loft tells you that the garden cannot
The most useful half hour in any roof assessment is spent in the loft, with a torch, looking up. Daylight is the first thing to find. Light showing between the slates or tiles means the covering is open, though a hairline of light at a gap in old boarding can also be a ventilation path, so context matters.
Damp timber and stains
Look at the rafters, the battens and the underside of the covering. Dark staining that follows a line down a rafter marks where water has run. Timber that is wet, soft or dusty-brown at the end grain needs probing with a blade. A little old staining that is dry and hard may be a repaired leak from years ago. Fresh, damp, spreading staining is a current one.
Underlay in poor condition
Underlay is the membrane laid beneath the covering as a second line of defence. Older roofs may carry bitumen felt gone stiff and ragged, with daylight coming through it, or no underlay at all. Where the underlay is perished, the covering above is doing all the work, and every slipped tile becomes a direct path for water. Underlay varies with the product and the roof, so we judge it by inspection rather than by age. We look at whether it is intact and whether it sags between the battens, and photograph it for you.
Take your own photographs of the loft if you can, with a note of the date. They give any surveyor a starting point and a record for later comparison.
Smell matters too. If you notice a musty smell, beads of water under the sarking boards or mould growing on timbers, tell us. Ventilation problems and leaks can look alike, and the cure for one is not the cure for the other.
Sagging, dipping and a roofline that has moved
Stand back across the road and look along the ridge, the line where the two slopes meet, and along the eaves. Both should be reasonably straight. A ridge that dips between its ends, a slope that bellies out, or an eaves line that waves are all signs that something beneath the covering has moved.
Common causes include rafters that have been weakened by decay, a purlin (a horizontal timber that supports the middle of the rafters) that has bent under load, or a roof that was never quite strong enough for the covering it carries. Heavy stone and slate roofs are especially unforgiving, since the weight bears on every timber all the time. Cotswold District Council's technical guidance records stone slate at about 1,000 kg per 10 m² of roof, so even a small loss of timber strength matters.
Wet, soft or bouncing
Sagging with signs of damp is more worrying than sagging alone. Old distortion that has not changed in decades is often tolerable. A new dip that has appeared since the last winter is not. Photograph the line with a fixed point beside it, such as a chimney or a neighbour's gable, and compare the picture a few months later. A tape measure held against a rafter inside the loft does the same job.
Sagging is the symptom most likely to need more than a new covering. It is also where a survey earns its fee, because timbers can only be judged from inside and above. If rafters or battens have to be renewed, our guide to replacing roof timbers explains the work.
Leaks that return after repair
One leak, traced and fixed, closes the file. A leak that comes back, or a second stain on a different ceiling within a season or two, is the strongest warning there is. Water enters a roof at the weak points, and finding that more than one has failed implies that the common cause is the age of the materials.
It is worth knowing how hard it can be to trace a leak. Water often enters at one point and travels along a timber or the underlay before it drips, so the stain on the ceiling and the hole in the roof may be metres apart. A roofer who patches the stain's neighbourhood and finds nothing wrong has not necessarily fixed it.
Check these before blaming the covering
Not every leak is a covering failure. Chimney flashings, lead valleys, blocked gutters and failed roof window seals all produce ceiling stains. We check them first, because replacing a whole roof to cure a failed flashing would be a waste. Our page on repairing or replacing a roof sets out how that decision is reached.
MyBuilder's repair guide gives £150 to £1,500 as a typical range for a roof repair overall, with minor jobs at £100 to £300 and major ones at £2,500 and above. Past a certain point, repeated spending on one roof makes the cost of replacement look more reasonable, though the comparison is only fair once the survey has priced both routes.
Age, moss and the limits of looking
A birthday is not a verdict. Natural slate is quoted at 80 to 100 years or more by MyBuilder, and stone slate can last a century or more with upkeep, so an old roof can be a sound one. Concrete tile sits at 30 to 50 years in the same MyBuilder guide, though Marley quotes about 60 years while calling that no guarantee. A roof falling within those ranges deserves a closer look, not an automatic quote. A roof outside them, with sound fixings and dry timbers, may still have years left, and nobody should sell you a new one on the calendar alone.
Our companion guide on roof age versus condition goes into that balance.
Moss and lichen
Moss on its own is cosmetic in the first instance, and clearing it is cheaper than replacing anything. MyBuilder gives manual scraping at £5 to £10 per m², and adds that a pressure washer risks damaging delicate tiles. Heavy moss that has lifted tiles, blocked gutters or kept the roof wet for years may have shortened the covering's life, but it is a symptom to weigh, not a verdict.
The limits of a ground-level look
From the garden, you can see the covering's surface. You cannot see the underlay, the fixings or the timbers, and those decide the answer. That is why a survey is not optional once two or three of these signs appear together. Roof inspections typically cost £150 to £500 according to MyBuilder (standard £150 to £250, drone £200 to £400), and the written report is worth more than a verbal opinion over a fence.
How a survey confirms replacement
A proper survey answers four questions. Is the covering failing across its area or only in patches? Are the fixings sound? Is the underlay intact? Are the timbers dry and strong? The photographs come from your own roof, taken outside and inside the loft, so you can judge the evidence yourself.
The result is a clear recommendation, with evidence: repair this, monitor that, or replace the lot. Where a repair will do, the report says that, because a repair costs far less than a new roof. Where replacement is the sensible route, the quote you receive afterwards gives scaffold and stripping, materials and labour, waste and making good a price of their own. MyBuilder puts a full re-roof at £5,000 to £12,000 typically, and the scaffold alone at about £1,125. The exact cost depends on the size, access and covering, and on whether the timbers need work after the old covering is lifted, which is why we price the survey findings and not a guess.
What happens next
If the survey points to replacement, the sequence of work is described step by step in the roof replacement process guide. Consent can set the timetable, so if yours is listed or in a conservation area, start with the guide to re-roofing a protected home first.
The replacement carries our 10-year workmanship guarantee in writing. Ring 01453 933613, message us on WhatsApp, or use the enquiry form, and tell us which of the signs above you have noticed, with a photograph if you have one.