Refurbishment
Flat roofs are our trade across South London, which is why this page argues for three options instead of the one that pays best: repair it locally, lay a new membrane straight over the old, or strip it back and renew it. Which one your roof gets is settled by an inspection, priced afterwards rather than guessed at, and set down with the reasoning attached.
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The short answer: Three routes exist for a worn flat roof: a localised repair, a new membrane laid over the old, or a strip back to the deck. An inspection settles which, because the choice depends on how much sound covering and dry boarding remain.
Straight talk
Right when faults are isolated and the covering is otherwise sound: a split at a lap (an overlapping seam), a cracked upstand (a turned-up edge at a wall), a failed detail. The cheapest option, and often all a roof needs.
Flat roof and leak repairsRight when the covering is worn out but the deck and insulation beneath are dry and well bonded. Our recommendation is liquid-applied waterproofing, HYDRONYLON worked over an inspected covering; a felt overlay is the exception, and the quotation gives the reason whenever it is one. Either way the strip-off is avoided. An overlay is the full system over an existing base rather than a reduced one: what changes is not the specification but what stays underneath it, and with that the age and falls the roof keeps.
Right when moisture has got beneath the membrane, the deck is damaged, or failure is widespread. Costs most, but resets the roof completely instead of covering a problem over.
Flat roof replacementEvidence
Whether you call it refurbishment or restoration, the decision is evidence, not preference. An inspection establishes the facts that matter: is the surface underneath dry, is the existing covering still stuck down, what state are the upstands and details in, and what can the structure take. Overlaying a wet roof traps moisture and buys a few years at the cost of the deck; stripping a dry one wastes money and fills a skip for nothing. The inspection exists so neither happens to you, and where the findings are wanted as a document for somebody else, a written condition survey is the paid option. Before you commission anything, the questions worth putting to any roofer are worth having to hand. On a large commercial roof where the inspection leaves all three options open, the assessment we carry out on large roofs weighs each one against measured evidence.
Converting to a warm roof costs least once the old covering is off, though an insulated overlay can make the change without stripping anything on a dry deck whose upstands are tall enough for the extra depth, and what that warm roof conversion involves on site has its own page.
Systems
Liquid is the route we recommend, and the reasoning is structural rather than a matter of taste. Overlaying in felt asks the building to hold a second sheet covering on top of the first, and every sheet brings joints with it, which is where flat roofs give way. Cold-applied liquid cures as a single piece with nothing to open, follows the details rather than being cut around them, needs no flame near anything combustible, and weighs a fraction of what it replaces.
That does not make liquid right everywhere, and the conditions on this page do not move: the existing roof still has to test dry through its layers, hold firmly to what it sits on and take preparation without breaking up. Where a roof genuinely suits a fresh built-up system instead, a felt overlay is specified and the quotation says why, whether that is the detail count, what is already up there or the weather the job has to be finished in. The system named in your quotation is the one the roof argued for. Where the roof you are overlaying is itself felt, the tests it has to pass are set out for existing felt roofs.
Money
We price each viable option in writing after inspecting the roof, and the logic is consistent: repair costs least; an overlay saves the strip-off, disposal and much of the disruption; strip and renew costs most and delivers a completely new covering. Where options are genuinely close, we say so and explain the trade instead of steering you to the dearest one.
The decision
Which of these you have is largely an accident of where the building stands. Interwar suburbia out towards Petts Wood and Orpington or New Malden and Tolworth is full of felted garage roofs; the mansion blocks and converted wharves nearer town, in Rotherhithe and Bermondsey for instance, throw up asphalt and concealed parapet work instead.
The three options above apply to whatever is already up there, but what is already up there changes the detail of the answer. These pages take each common covering in turn: how it fails, what an inspection checks on it, and where its own limits sit.
One building type reaches these three options from somewhere else entirely. The roof over a garage is usually the oldest on the property and frequently the only one nobody has ever renewed, so it arrives without the insulation finding that settles most of these arguments and decides on the boards alone.
Lead, concrete and glass reinforced polyester all turn up on London roofs too, and none of them has a page here yet. For each of them the work is repair, and an overlay wherever the substrate allows one, once an inspection has identified the surface and an adhesion test carried out up there has had its say. Concrete and screed are among the surfaces our liquid system's assessment names; lead and glass reinforced polyester are not, so what any guarantee then covers is written into the quotation. Ask about yours and you will get the same answer in writing.
Whichever of the three a roof ends up having, we offer a repeating maintenance visit on it once the work is signed off, quoted for that roof and chargeable from the first one. What sits inside that fee, and what is priced on its own, is set out under aftercare on the planned maintenance page.
Questions
No. If the deck, the structural boards a flat roof is built on, and the insulation underneath are dry, a localised repair or a full overlay is often the better answer, at a fraction of the cost and disruption of replacement. Replacement is the right call when moisture has spread beneath the membrane or the covering has failed across its whole area.
An overlay is a new waterproof layer installed over the prepared existing covering. One thing it does not dodge: renewing a covering right across a roof can bring its thermal performance into scope in the same way a strip and renew does, so the insulation question belongs in the same conversation. We recommend cold-applied liquid waterproofing, because it hardens into a single piece and asks almost nothing extra of the structure holding it. Torch-on felt over the top is the exception rather than the norm, taken where a roof suits it. Where the base underneath is dry and sound, either saves the cost, disruption and waste of tearing that base off.
When the inspection finds wet insulation or a damaged deck, when previous coverings have been layered too many times, or when the roof has failed widely rather than locally. At that point an overlay would trap the problem, so the honest option is to strip back and rebuild the covering properly.
With evidence from an inspection: whether the surface underneath is dry, how well the existing covering is still stuck down, the state of the details, and what the roof structure can take. The decision goes into the quotation with the reasoning, so every option, recommended or ruled out, arrives with the thinking that put it there.
There is no honest single figure: the cost depends on the option, the size, the access and what the inspection uncovers. The logic is consistent though: repairs cost least, overlays avoid the cost of stripping and disposal, and replacement costs most but resets the roof completely. You get each viable option priced in writing.
Review
Very professional. Highly recommend. We'll be using services again in the future.
That is exactly what an inspection answers. Tell us about the roof and we will take it from there.
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Coming out and pricing the work is free, and every quotation for an existing roof comes with photographs of it. A written condition survey carries a fee, agreed before the visit and taken off the price of the work if you go ahead.
