Every Cornerstone roofing project carries a 10-year insurance-backed warranty, alongside the relevant material guarantee from the manufacturer.
Reliable, high-quality work before, during, and after the scaffold comes down.
Cornerstone Roofing installs new flat roofs and replaces old ones across Mid Sussex, on extensions, loft conversions, porches and summer houses through to commercial buildings. We fit six flat roofing systems: built-up felt, EPDM rubber, GRP fibreglass, single ply membranes, liquid applied membranes and green roofs, each set out further down this page. Because we fit all six, the system we recommend is the one that suits your roof, not the only one we know how to lay.
Replacing a flat roof means more than laying a new covering over the old one. The old roof is stripped back to the deck, the deck is checked and repaired where it needs it, and the falls, upstands, edge trims and outlets are put right before the new system goes on. How well a flat roof performs is largely decided at that stage, which is why we price it from a survey rather than from a plan.
Every new or replacement flat roof starts with a free site survey. We look at the deck, the falls and the existing covering, recommend a system, and set the specification and the scope out in writing before anything is booked in. Our flat roofing installations carry a 10-year insurance-backed warranty on workmanship alongside the relevant manufacturer guarantee on the membrane fitted.
If the whole roof needs doing, pitched sections included, see our roof replacement page. If it is a split seam, a lifted edge trim or perished flashing rather than a failed roof, our roof repairs service covers flat roof repairs across Sussex.
Our flat roofing systems are not limited to traditional uses. We install and replace them on:
Whatever the building, the same handful of things decide whether a flat roof lasts: the falls, the condition of the deck, the detailing at the edges and upstands, and a covering matched to how the roof will actually be used. We look at all four on site before recommending a system, so the quote you get is for the roof in front of us rather than a standard specification applied to every job.
Commercial flat roof installation and re-covering is a different job from a domestic one. The roof usually has to be replaced while the building stays in use, plant and access have to be worked around, and the contractor is expected to clear prequalification before anyone gets on site. We quote commercial flat roofing across Mid Sussex, a patch that sits mostly in West Sussex and runs over the county line into East Sussex. Single ply is the covering most commercial flat roofs are re-covered in: the single ply section below sets out how it goes on, and the accreditations that come with the work.
A flat roof that leaks in one spot after a storm is usually a repair. A flat roof that has blistered across the whole surface, that holds standing water long after the rain has stopped, that is splitting along the seams, or that is showing damp on the ceiling in more than one place, has generally passed the point where patching it is worth the money. Our flat roof repair guide sets out what usually fails and when a patch is still the sensible answer.
On a flat roof replacement the old covering comes off, the deck and any insulation get inspected while everything is open, and anything soft or saturated is dealt with before the new system goes on. That stage is what decides whether the new roof lasts, and it is precisely the part nobody can price without looking. A new flat roof on an extension or a loft conversion follows the same order of priorities: get the falls, the deck and the detailing right first, then choose the covering.
Not sure which of the two you are looking at? Book a free site visit and we will tell you which, in writing, with the reasoning set out so you can weigh it up yourself. If the property needs the whole roof done rather than just the flat section, we cover that on our full roof replacement and re-roofing page.
We install six flat roofing systems, set out below. They differ in how they are installed, how they handle foot traffic and complex detailing, how they look once finished, and how long they are expected to last. There is no single best flat roof: the right answer depends on the size and shape of the roof, what sits underneath it, whether anyone needs to walk on it, and the finish you want. Tell us what the roof has to do and we will recommend the system that suits it, then quote it in writing. Our flat roof materials comparison goes into more depth on how each system performs over time.
We install and re-cover flat roofs on blocks of flats, offices and commercial buildings as well as on homes. If you manage a block for its freeholder or residents, look after an office, or own a commercial unit, the roof usually has to be replaced while people carry on using the building underneath it, so access, hot works and weather protection are planned before the old covering comes off.
We are CHAS accredited at both Standard and Elite level. CHAS Standard covers the SSIP-recognised health and safety assessment that commercial sites and main contractors ask for, while CHAS Elite certifies us against the Common Assessment Standard, the broader industry prequalification that main contractors and public sector bodies increasingly require. The rest of the accreditations behind our commercial roofing in Haywards Heath and Mid Sussex are on our homepage.
Most commercial flat roofs are re-covered in single ply, the last of the six systems below. For a block of flats or an occupied office, we survey the roof on site and quote from what we find.
Built-up felt roofing is the traditional flat roofing system: layers of bitumen felt bonded together into one continuous waterproof build-up and finished with a mineral cap sheet. Modern torch-on felts are a long way from the thin single-layer roofs that gave felt its old reputation, and they remain one of the most cost-effective ways to cover a flat roof properly.
Felt is the covering we are asked to replace most often. A tired felt roof that is blistering, splitting or letting water through is usually stripped back to the deck and rebuilt rather than patched indefinitely, because each patch buys less time than the one before it. All of our torch-on work is carried out to Safe2Torch guidance, which governs how hot works are managed around the vulnerable details on a roof.
Ask us to quote a felt roof replacement and we will get the old covering assessed and the deck inspected first, so the quote reflects the roof you actually have.
EPDM is a synthetic rubber membrane laid as a single sheet, so on most domestic flat roofs there are no joints across the field of the roof at all. That is the whole point of it: seams are where flat roofs usually fail first. It is light, flexible, and resistant to UV and ozone, which is why it has become such a popular choice on domestic flat roofs.
Because it is fully bonded and stays flexible in cold weather, EPDM copes well with the movement a flat roof goes through over a year. It is a long-life covering, and we will give you the manufacturer’s expected service life and guarantee in writing alongside your quote rather than a headline figure that may not match the system actually being fitted.
We install EPDM both on new flat roofs and as the replacement covering once an old felt or asphalt roof has been stripped off.
A green roof puts a growing layer over the waterproofing. Sedum blankets are the usual choice on domestic roofs, with deeper build-ups where the structure allows. They insulate, they slow the run-off from heavy rain, and they turn a flat roof that was dead space into something worth looking at from the window above it.
A green roof is only ever as good as the waterproofing underneath, so the membrane, the drainage layer and the green build-up are specified together as one system rather than bolted on to each other. The deck also has to carry the extra weight, wet as well as dry, which is one of the first things we look at on site.
If you want the insulation and ecological benefits, raise it at the free visit and we will tell you honestly whether the structure suits it.
GRP, or fibreglass, is laid wet over a new timber deck and cures into one seamless sheet with no joints and no welded laps. It is hard-wearing and walkable, which makes it the system to ask about where a flat roof doubles as a balcony or a terrace, or where it gets crossed regularly for access.
GRP takes colour-matched trims and a choice of finishes, so it tends to get picked where the roof is in view from a window or from the garden. It does need a sound, dry deck and settled weather to lay properly, which is part of why we survey a roof before quoting it rather than pricing flat roofs off a plan.
We install GRP on new flat roofs and as a replacement covering.
Liquid roofing is applied wet and cures into a seamless, fully bonded membrane that takes the shape of whatever it is laid over. That makes it the answer for the roofs sheet systems struggle with: pipe penetrations, plant plinths, awkward upstands, box gutters, parapets, and roofs with a lot of detail packed into a small area.
A liquid roof coating is also the least disruptive way to bring an existing roof back into service where the covering is tired but the deck below is sound. Liquid systems can be applied over many existing substrates, including felt, asphalt and concrete, so in the right circumstances the old roof stays where it is and the building carries on being used while the work goes on above it.
What is underneath decides whether coating is genuinely the right call or whether you are better off replacing the covering outright. We will tell you which of the two we would do, and why, before you commit to either.
Single ply membranes are the standard covering on commercial and industrial flat roofs: factory-made sheets, mechanically fixed, adhered or ballasted, with the laps hot-air welded rather than glued. They go on quickly, they are light enough for large spans and for existing structures, and they take the movement a big roof goes through in its stride.
It is the system to specify where a commercial or industrial roof needs re-covering, and it works equally well on a large or complicated domestic flat roof. Work of this kind usually arrives with prequalification attached, which is where our accreditations earn their keep: Cornerstone Roofing is CHAS Standard and CHAS Elite accredited for health and safety, a member of the National Federation of Roofing Contractors, and Trustmark registered. Access on the larger jobs runs through The Cornerstone Group, which includes a dedicated scaffolding company.
If you are pricing a commercial re-cover or specifying single ply on a new build, send us the drawings or the roof area and we will quote against them.
We install, replace and repair flat roofs throughout Mid Sussex and the surrounding villages from our base in Scaynes Hill, on homes, extensions, conversions and commercial buildings alike. If your property is nearby but not on the list, it is still worth asking.
Flat roof costs depend on the size of the roof, the membrane chosen (built-up felt, EPDM rubber, GRP fibreglass, single-ply, liquid-applied or green-roof systems), insulation upgrades, edge details, and any structural deck repairs needed once the old covering is stripped. Rather than quote a misleading ballpark, we book a free site visit and provide a written quote based on your specific roof.
Flat roof timescales depend on the size of the roof, the membrane being installed, site access, the weather, and the condition of the deck and insulation underneath. Smaller roofs such as porches, garages or single-storey extensions are often wrapped up in a few days, larger residential or commercial flat roofs typically run for a few weeks, and projects involving full deck or insulation rebuilds can take longer. We’ll give you a timeline in writing alongside your quote.
There is no single ‘best’ flat roof material. The right choice depends on the roof’s use, the appearance you’re after, the lifespan you’re aiming for, and the budget you want to plan around. We install built-up felt (cost-effective, well-proven), EPDM rubber (long-life, single-piece membrane), GRP fibreglass (seamless, tough, walkable), single-ply membrane (commercial-grade, fast install), liquid-applied membranes (great for awkward shapes and tricky detailing), and green roofs (insulating, ecological). We’ll talk you through the trade-offs at the free visit.
Watch for pooling water that doesn’t drain within a day or two, blisters or bubbles in the surface, cracks, splits, lifting seams, exposed felt or fibres, damp staining on internal ceilings, and a covering that’s noticeably brittle or chalky to the touch. Where damage is localised on a sound deck, a targeted repair is usually enough. Widespread blistering, recurring leaks or a saturated deck normally point to a full replacement.
Yes. Flat roof repair is one of our most-requested services across Sussex, covering everything from leaking porches and blistered garage roofs to split seams on single-storey extensions and failed parapet details. We work throughout Mid Sussex from our base in Scaynes Hill, including Haywards Heath, Burgess Hill, Cuckfield, Hurstpierpoint, Hassocks, Lindfield and the surrounding villages.
If the deck underneath is sound and the damage is localised (a split seam, a small puncture, perished flashings, lifted edge trims), a targeted repair will usually keep the roof watertight for years. We only recommend a full replacement where the membrane has widely failed, the insulation is saturated, or the deck has rotted, and we’ll always set out the trade-off in writing so you can decide.
Our flat roof installations come with a 10-year insurance-backed warranty on our workmanship, alongside the relevant manufacturer guarantees on the membrane fitted (EPDM, GRP, single-ply and similar systems all carry their own product-level warranties). The full terms are set out in writing alongside your quote.
