Every roofing job begins with the same fork. Patching costs a fraction of re-covering, so the sensible instinct is to patch, and often that instinct is right. The trouble arrives when a roof is repaired a fourth time and the money spent on repairs begins to approach the cost of the job it was meant to avoid.
This guide is a way of deciding, not a list of warning signs. If you want the symptoms first, our page on the signs a roof needs replacing covers them. Here we work through five tests in the order a surveyor applies them: age set against condition, how far the failure extends, what lies beneath the covering, what each route costs over ten years, and what you plan to do with the house. Most roofs answer clearly by the third test.
Test one: age set against condition
Age on its own tells you very little, but it tells you where to look harder. Published lifespans give a rough frame. MyBuilder puts a slate roof laid properly at 80 to 100 years or more, and Marley, a tile maker, quotes roughly 60 years for its concrete tiles, with a caveat that the figure promises nothing. MyBuilder puts concrete tiles at 30 to 50 years before replacement, and clay at 40 to 60. Sources disagree because exposure, workmanship and maintenance differ from roof to roof.
The useful reading is this. A covering in the first third of its likely life with one failed section almost always wants a repair. A covering in the last third that is failing in several places is a different case, because each repair buys less time than the one before it.
Condition beats the calendar. A sixty-year-old slate roof with sound slates and a few rusted nails can outlast a twenty-year-old roof laid on thin tiles and poor battens.
How do you judge condition from the ground?
You can learn a fair amount without a ladder. Look along the ridge line for dips, which suggest tired timbers. Look for tiles that have lost their surface, a sign of crumbling concrete, and for slates that have slid below their neighbours. Binoculars from the garden show more than a phone photograph. Stand back far enough to see the whole slope at once, because a roof that looks even from across the road usually is. Anything that needs you to step onto the roof is a job for a surveyor, and our guide on how long a re-roof takes shows what the work looks like once you decide on it.
Test two: how far the failure extends
The next question is whether the fault is a single spot or a general condition. A cracked tile, a slipped slate, a lifted piece of flashing and a split in a flat-roof seam are all of this kind. A repair cures them, and everything around them keeps working.
General conditions are different. Slates held on by corroded iron nails will keep slipping, one after another, in lines across the slope. Concrete tiles that have lost their face and begun to flake absorb water rather than shed it. A flat roof blistered all over is telling you the felt has run its course, and a patch over one blister leaves the others where they were.
Can I replace only one slope?
Sometimes. If a single slope has failed and the other is sound, replacing that slope alone can be sensible, particularly on a house where one side faces the prevailing weather. It stops being sensible where the two slopes share a ridge, valley and abutment details that the new work has to tie into, since matching old and new coverings can be awkward. Our page on replacing one side of a roof sets out when it works and when it does not.
Does a bigger repair change the Building Regulations position?
It can. Planning Portal guidance sets two limits. Staying under 25 per cent of the total building envelope and under 50 per cent of the roof usually means no application to building control for the repair or re-covering. Pass either limit and approval applies. A partial re-cover therefore sits on a threshold, and our page on re-roofing and building regulations explains how the tests work.
Test three: what the underlay and battens are doing
The covering is the part you can see. The part that decides repair or replacement is often the part you cannot. Underlay is the waterproof membrane laid over the rafters beneath the tiles or slates. Battens are slim timber laths fixed across the rafters, and the covering is hooked or nailed onto them. Together they are the second line of defence, and they date from the same day as the roof.
If both are in good order, a repair above them is worth doing, because the roof has a working skeleton. If the underlay is torn or perished, or there never was one, as is common on older terraced houses, rain that gets past a defective tile reaches the loft with nothing to stop it. If battens are rotten, tiles cannot be refixed securely, and a repair becomes a temporary measure.
How can battens be checked without stripping the roof?
From inside the loft, shine a torch at the roof's underside. Daylight showing between tiles, dark staining on the timbers, and soft or crumbling battens each point to trouble. A moisture meter on the rafters shows whether damp is a one-off or a persistent condition. The survey photographs include the loft side for this reason, since the underside of a roof often tells you more than its upper face.
Where the underlay and battens are spent, replacing them means taking the covering off, and at that point re-covering the whole roof usually makes more sense than relaying only a patch. If your loft is empty and you may convert it later, read about putting a new roof over an empty loft first.
Test four: what each route costs over ten years
Price comparisons mislead when they stop at the first invoice. A better habit is to add up what each route is likely to cost across a ten-year horizon.
MyBuilder's roof repair guide, updated 21 August 2026, gives national figures of £100 to £300 for a minor repair, £500 to £1,000 for a moderate one and £2,500 or more for a major one. Its new roof guide puts a full replacement at £5,000 to £12,000. Our separate guide to what a new roof costs sets out those figures in detail.
When do repeated repairs add up to a new roof?
Take a roof that needs a moderate repair now and another in two years as more slates fail. At MyBuilder's national figures, four moderate repairs over a decade cost £2,000 to £4,000, and that money buys no more life from the covering, since the underlying problem is still there. Against that, a replacement at the low end of the national range is £5,000, and it resets the clock. The sums do not always favour replacement, and a roof whose faults are genuinely isolated can be repaired cheaply for years. What the sums do show is that a roof demanding repair every year or two has stopped being a repair case.
Remember the costs around the job too. Scaffold, if a repair needs it, is charged once whether the work is small or large, so a series of small repairs that each need scaffold can cost more than one planned job. Checking whether a quote includes VAT and any scaffolding stops a repair looking cheaper than it is.
A repair that fixes a fault is good value. A repair that postpones a replacement for a year is a loan, and the interest is paid in the next storm.
Test five: what you plan to do with the house
The last test has nothing to do with the roof and everything to do with your plans. Two homeowners with the same roof can reach opposite answers.
Staying put for ten years or more
If you intend to live in the house for a long time, a replacement is an investment in the home you use. You gain the full life of the new covering, and every year without leaks, damp or repair visits is a year of the roof working as intended. A full re-roof also opens the door to other work, such as loft insulation, new fascias and gutters, or panels for solar. Stripping and renewing more than half the roof can bring a thermal upgrade into play under Part L, which is both an extra cost and a benefit, and our page on Part L and re-roofing explains when that happens.
Selling within a year or two
A buyer's surveyor will look at the roof, and a tired covering gives a buyer something to negotiate over. Replacing the roof before sale may not return its cost in the price, and a sound repair, with the work documented, is often enough to keep a sale moving. The right answer depends on the condition and on the market, and dated photographs from a roof survey give you something concrete to put in front of a buyer.
Whichever applies, put the dates in writing before you decide. Knowing roughly when you expect to move turns a vague worry about the roof into a sum you can actually work out.
Letting the property
A let house needs a roof that does not demand attention, and tenants rarely welcome scaffold at short notice. A planned replacement removes the risk of emergency call-outs on an occupied home, and the date is yours to choose.
Putting the five tests together
Taken in order, the tests give a fairly firm result. A young covering, a local fault, sound underlay and battens, repairs that cost less than a fraction of replacement and an uncertain length of stay add up to a repair. An old covering, a failure that runs across a slope, perished underlay or rotten battens, a history of recurring repairs and a long stay ahead add up to a replacement. Most roofs sit between, and the surveyor's job is to say which side they lean towards and why.
That judgement is why we survey before we quote. We would rather advise whatever work cures the problem and no more, so where a repair would hold, the written quote says so even though the job is smaller. Where it will not, the photographs from your own roof show you why, and the quote is a single total for the replacement. Nothing is decided on the doorstep, and you have time to read the photographs, ask questions and compare the quote with any other you hold.
If we do replace, the work comes with a written 10-year workmanship guarantee, which speaks to the fitting and not to the materials, and the site is cleared with the waste taken away. Our roof replacement page describes the process from survey to final clear-up.