Short answer: in the UK, refurbishing a flat roof with a liquid-applied waterproofing system usually costs less than tearing the roof off and replacing it, because there is no strip-off, no waste disposal and less time on site. As a rough guide, installed refurbishment tends to fall in the region of £70 to £150 per square metre, depending on the system, the condition of the existing roof and access. A full replacement, by comparison, is usually priced per square metre too: roughly £150 to £250 per square metre for a like-for-like recover, rising to around £250 to £300 per square metre for a full warm-roof replacement that adds insulation and scaffolding, with London at the upper end.
Every roof is different, so treat every figure here as a rough guide only, not a price we can promise. The only accurate number is a written quote based on a survey of your actual roof.
Why refurbishment is usually cheaper than replacement
A full flat roof replacement is not just the new covering. The quote also has to cover stripping the old roof, skip hire and waste disposal, more scaffolding time, and almost always new deck boards, because once the old covering is stripped the boards underneath are rarely sound enough to leave in place. Those extras add up quickly.
Refurbishment with a liquid-applied system works differently. The new waterproofing is applied straight over the existing roof, provided that roof is sound enough to overlay. That removes the cost of tear-off and disposal, shortens the time on site, and avoids opening the building up to the weather. You are paying for preparation, materials and labour, not demolition. As long as the existing deck is structurally sound, the roof is not stripped back to the boards, so there is no risk of an unexpected deck replacement appearing mid-job once the roof is opened up.
This is also why refurbishment is often possible while the building stays in use. There are no hot works and no roof left open overnight.
A worked example
Figures depend entirely on the roof, but a worked example shows where the spread comes from. Take a 40 square metre extension roof:
- Refurbishment with a liquid-applied system, where the existing roof is sound enough to overlay: roughly £2,800 to £6,000 (about £70 to £150 per square metre).
- Like-for-like replacement, stripping the old covering, replacing the deck boards and recovering: roughly £6,000 to £10,000 (about £150 to £250 per square metre).
- Full warm-roof replacement, adding insulation to meet current building regulations, with scaffolding: roughly £10,000 to £12,000 (about £250 to £300 per square metre).
The wide spread is not vagueness. It is the difference between overlaying a sound roof, swapping the covering, and rebuilding the roof with new insulation. The more you strip off and rebuild, the more you pay. The replacement figures here assume new deck boards, which is one reason they sit above the headline numbers in many online guides. These are rough guides to show the shape of the cost, not quotes.
Why online price guides look lower
Most online cost guides quote a lower number than a real London contractor will, and it is worth knowing why. They usually price the covering only, on a sound existing deck, with no allowance for replacing the deck boards, which a genuine like-for-like replacement nearly always needs once the old covering comes off. Many also use national averages or material-only prices and leave out scaffolding, waste disposal, minimum job charges and VAT. London and the South East sit above national rates on top of that. A full quote that includes the deck and everything else will be higher than a headline figure, and more honest about what the job actually costs.
What affects the price
A few things move a refurbishment quote up or down:
- Roof size. Most systems are priced per square metre, so area is the main multiplier. Very small roofs can carry a minimum job charge, which raises the effective rate per square metre.
- Economies of scale. The bigger the roof, the lower the rate per square metre tends to be, because fixed costs like set-up, preparation and access are spread over more metres. A small roof almost always costs more per square metre and sits nearer the top of the range.
- Condition of the existing roof. A sound roof that needs cleaning and priming costs less than one that needs blisters cut out, splits repaired and ponding areas built up first.
- The substrate. Felt, metal, PVC and mineral surfaces each need different preparation and priming, which affects labour and materials.
- Detailing. Upstands, parapets, outlets, pipe penetrations and rooflights all take time to waterproof properly. A plain rectangle is cheaper per square metre than a roof full of detail.
- Access. A ground-level garage is straightforward. A second-storey roof needing scaffolding, or with restricted access, will cost more.
- Location. London and the South East typically carry a premium over national rates.
The honest way to compare cost
The cheapest quote on the day is not always the best value. A more useful measure is cost per year of service life, what you actually pay spread over how long the roof lasts before it needs attention again.
A cheap covering that needs redoing in a few years can work out more expensive than a more durable system that is left alone for far longer. When you compare quotes, ask what is guaranteed and for how long, not just the headline price.
When refurbishment is the right call, and when it isn’t
Refurbishment makes sense when the existing roof is structurally sound but the waterproofing has aged, is leaking at the details, or has reached the end of its life on the surface. Overlaying restores watertightness without the cost and disruption of replacement.
It is not the right answer for every roof. If the deck underneath is rotten, the insulation is saturated, or the structure itself has failed, those problems have to be dealt with first, and that can mean replacement. An honest contractor will tell you which situation you are in after a survey, rather than coating over a problem.
Where the HYDRONYLON® system fits
HYDRONYLON is a liquid-applied flat roof waterproofing system, applied cold straight over felt, metal, PVC or mineral roofs, with no strip-off. It cures into one seamless membrane, with the joints and details that usually leak first reinforced as part of the system.
It is installed only by HYDRONYLON Approved Contractors, who issue a 10-year product guarantee on the materials, and the system is certified under European Technical Assessment ETA-23/0735. Because there is no tear-off and no hot works, refurbishment is usually quicker and less disruptive than a full replacement.
How to get an accurate price
There is no substitute for a survey. The condition of your roof, its size, its details and access all change the figure, so a contractor needs to see it before quoting.
Whether you are a homeowner, a commercial property owner or a managing agent looking after a block, the system is applied by our Approved Contractors, who will survey the roof and quote for the work. You can find them on the Approved Contractors page.