Liquid roofing for flat roofs in London
Liquid roofing waterproofs a flat roof by sealing over the covering you already have, rather than stripping it off. If you are weighing up how to fix a failing London flat roof, this page sets liquid roofing against the other options so you can see where it fits. HYDRONYLON® is a certified liquid roofing system, supplied by HYDRONYLON LTD and installed across London by Approved Contractors, so the step from here is to reach a contractor who fits it.
Your options for a failing flat roof in London
When a flat roof starts to leak or pond, there are really three routes: replace the covering, patch the failures, or seal the roof with a liquid-applied membrane. Each suits a different situation, and the right one depends on the state of the roof underneath. Here is how they compare for a typical London flat roof.
| Full replacement | Patch repair | Liquid roofing | |
|---|---|---|---|
| The existing roof | Stripped off and taken away | Left as it is | Stays in place, sealed over |
| Time on site | A week or more | Hours | A few days |
| Flame on the roof | Often needed | Sometimes | None, cold applied |
| Waste | Old roof to the skip | Little | None |
| The building below | Often closed off | Brief interruption | Usually stays in use |
| What you are left with | A brand-new covering | One area fixed, for now | One seamless membrane over the whole roof |
| Relative cost | Highest | Lowest now, but it recurs | Below a full replacement |
Full replacement makes sense when the structure or deck is past saving. Patching has its place for a single, isolated fault. Liquid roofing sits between the two: it treats the whole surface in one membrane, over a covering that is sound enough to stay, without the cost and upheaval of a full strip-off.
When liquid roofing is the right choice, and when it isn’t
Liquid roofing is a good fit when the existing covering is worn but the structure below it is sound: the deck is solid, the roof is dry underneath, and the failures are at the surface, the laps, seams, upstands and details. In that case sealing over the roof gives you a fresh, continuous waterproof layer for a fraction of the disruption of a re-roof.
It is not always the answer. If the deck is rotten, if water is already trapped in the build-up, or if the roof needs rebuilding for other reasons, an overlay only buries the problem. That is why a HYDRONYLON Approved Contractor surveys the roof first and will tell you honestly if liquid roofing is not the right call. A photo of your roof, sent by email, is enough to start that conversation.
The HYDRONYLON system, in brief
HYDRONYLON is a complete, certified system rather than a single product: a primer matched to your substrate, mesh reinforcement and a top coat, assessed together under European Technical Assessment ETA-23/0735. It is supplied by HYDRONYLON LTD, a British company, and the system itself is certified to a European standard, installed only by Approved Contractors in London, with a 10-year product guarantee on the materials, issued to the contractor who carries out the work. You can see the full build-up for each roof type on the applications page, and the step by step on the system page.
Liquid roofing projects in London
Real London flat roofs sealed with the HYDRONYLON liquid roofing system.
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Leaking felt roof sealed in Shepherd's Bush, London W12 Felt · 65 m² · 6 August 2025 A worn felt flat roof in Shepherd's Bush, London W12 was leaking into the flat below. See how the HYDRONYLON liquid-applied system sealed all 65 m² in four working days, with no strip-off. Read case study → -
Leaking lead and parapet roof sealed in Whitechapel, London E1 Lead & parapet · 78 m² · 18 August 2024 A pitched parapet roof on Whitechapel Road in London E1 was leaking through cracked, worn lead into the flats below. See how the HYDRONYLON liquid-applied system sealed the lead, parapet copings, valleys and details, with no lead replacement or tear-off. Read case study →
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Frequently asked questions
Is liquid roofing as good as a new roof?
For a roof whose structure is sound, a certified liquid roofing system gives you a fully waterproof surface without replacing the roof. It is assessed as a complete system and backed by a 10-year product guarantee on the materials. Where the deck itself has failed, a new roof is the better route, which is something the survey will establish.
Liquid roofing versus EPDM or fibreglass?
EPDM rubber and GRP fibreglass are coverings in their own right, usually fitted as part of a new roof. Liquid roofing is different: it goes over your existing covering and forms one continuous layer, with none of the seams a sheet system relies on. Which is right depends on whether you are replacing the roof or sealing the one you already have.
Can liquid roofing go over my existing flat roof?
In most cases yes. It is designed as an overlay for a sound covering, whether felt, metal, concrete or PVC, so the existing roof stays in place. The contractor confirms during the survey that the roof is sound enough to seal over rather than strip.
How long does liquid roofing last?
As a certified system, HYDRONYLON carries a 10-year product guarantee on the materials, an independently assessed working life. The result on your roof depends on the condition it goes onto and the contractor who applies it, which is why it is fitted only by Approved Contractors.
How much does it cost, and who installs it?
Cost depends on the roof's size, condition and detailing, so an Approved Contractor quotes on your roof. As a guide to what drives the price, see how much flat roof refurbishment costs. HYDRONYLON LTD supplies the system; the work is carried out by Approved Contractors across London.