We get calls every week from homeowners in Watford who are sick of their leaking flat roof and want something that actually works long-term. Nine times out of ten, we recommend EPDM rubber roofing. It's not the flashiest option — fibreglass looks a bit more polished — but for sheer reliability and value for money on a domestic flat roof, nothing beats it. The membrane is a single piece with no joints to fail, and it stretches rather than cracks when the building moves.
EPDM (Ethylene Propylene Diene Monomer) is a synthetic rubber membrane used for flat and low-pitch roofing. We primarily install the Firestone RubberGard system, which is the market leader, alongside ClassicBond and Permaroof as alternatives. The membrane is manufactured in large sheets — big enough to cover most domestic flat roofs in a single piece without any joins. That's what makes it so reliable: no joints means no weak points where water can find a way in. The membrane is bonded to the roof deck using a contact adhesive, with the edges tucked under aluminium trim or into a drip edge detail. We install EPDM as a warm deck system where possible, which means laying rigid insulation boards (Celotex or Kingspan PIR) on top of the existing deck and then the membrane on top of the insulation. This approach meets current Building Regulations Part L for thermal performance and means you get a better-insulated roof as part of the job. For properties in Watford, where a major town in south-west Hertfordshire with a wide range of housing from Victorian terraces to modern high-rise developments and suburban estates, EPDM is an excellent choice because it handles temperature extremes well — staying flexible in winter cold and not softening in summer heat. The membrane has a proven lifespan of 50+ years and comes with a manufacturer-backed guarantee of 20 years. It requires virtually no maintenance beyond keeping the gutters clear, and any accidental punctures can be patched with EPDM offcuts and adhesive.
Most EPDM installations we do in Hertfordshire are replacing old three-layer felt systems that have reached the end of their life. The felt cracks, blisters, and splits — especially at the joints between sheets and around upstands. Once the top layer goes, the lower layers follow quickly. Rather than patching felt yet again, EPDM gives you a permanent solution.
If water sits on your flat roof in puddles after rain, it's a sign the falls are inadequate. Standing water degrades most roof coverings faster and adds weight to the structure. When we install EPDM, we can build up falls using tapered insulation boards, ensuring water drains towards the gutters rather than sitting on the membrane.
Many older flat-roofed extensions and garages have little or no insulation, making the rooms below cold in winter and prone to condensation. A warm deck EPDM installation solves both problems — the rigid insulation boards go on top of the deck, bringing the roof up to current Building Regs standard and keeping the space below warmer and drier.
On older flat roofs, the upstand where the roof meets a wall is often the first point of failure. The felt peels away, the mortar fillet cracks, and water gets behind the covering. EPDM upstands are properly terminated with a mechanical batten bar or tucked into a raggle cut in the brickwork, giving a much more durable edge detail.
A typical garage flat roof replacement with EPDM in Watford costs £1,200-£2,000, depending on size and the condition of the existing deck. A rear extension flat roof — say 15-25 square metres — usually comes in at £2,000-£4,000. Per square metre, you're looking at £80-£120 fully installed with a warm deck insulation build-up. If the existing timber deck needs replacing (chipboard that's rotted, for example), that adds to the cost — new 18mm OSB3 sterling board typically adds £20-£30 per square metre including labour. Smaller jobs like porch roofs or bay window tops run £600-£1,200. These prices include all materials, labour, insulation, trims, and the manufacturer's guarantee registration. Scaffolding, if required, is extra at £400-£800 in Hertfordshire.
We use Firestone RubberGard EPDM membrane as our primary system — it's 1.14mm thick, manufactured in sheets up to 15m x 30m, and has the longest track record in the industry. For smaller jobs or budget-conscious customers, ClassicBond and Permaroof are excellent alternatives. Bonding adhesive is Firestone BA-2012 water-based contact adhesive. Insulation is Celotex or Kingspan PIR boards, typically 100-120mm thick to meet Part L requirements. Deck boards, where needed, are 18mm OSB3 (Sterling Board) with a smooth face. Edge trims are extruded aluminium from Freefoam or Manthorpe, in standard colours or powder-coated to match. All sealants are Firestone or Geocel products designed for use with EPDM.
We measure your flat roof in Watford, check the condition of the existing deck, assess the falls, and work out whether a warm deck or cold deck build-up is right for your situation. We'll talk you through the options and give you a written quote.
The old covering comes off. We check every inch of the timber deck for rot or damage and replace any boards that aren't sound. The deck needs to be clean, dry, and flat before the new system goes on — any imperfections show through the membrane.
For a warm deck build-up, rigid PIR insulation boards are laid and mechanically fixed. If a new deck layer is needed, 18mm OSB3 goes on top. We create the correct falls so water drains towards the gutters — no ponding.
The EPDM membrane is laid out, positioned carefully, and bonded to the deck with contact adhesive. The edges are folded into trims or terminated at upstands. Every edge detail is finished properly — this is where most flat roof failures happen, and we don't cut corners.
Aluminium edge trims are fitted, all penetrations (pipes, vents) are sealed with purpose-made EPDM boots, and the manufacturer's guarantee is registered. We walk you through the finished job and explain what (very little) maintenance is needed going forward.
Flat roofs are common across Watford on rear extensions, garages, dormers, and bay window tops. Watford is a major town in south-west Hertfordshire with a wide range of housing from Victorian terraces to modern high-rise developments and suburban estates. Many of these flat roof sections were originally covered in bituminous felt in the 1960s-80s and have been patched multiple times since. The South East of England gets enough rainfall to test any flat roof, and the freeze-thaw cycles in Hertfordshire are particularly hard on old felt — water gets into cracks, freezes overnight, and opens them up further. EPDM handles this brilliantly because the rubber stays flexible well below freezing. The thermal movement in building structures — which causes rigid coverings to crack — is absorbed by the elasticity of the membrane.
EPDM is proven to last over 50 years in real-world conditions. Compare that to 10-15 for felt. It's a one-and-done job — you won't be calling us back for a replacement in your lifetime.
A single sheet of rubber over your entire roof. No seams to split, no joints to fail, no overlaps where water can creep in. It's why EPDM rarely leaks when installed properly.
Every EPDM installation we do in Hertfordshire comes with a written guarantee from the membrane manufacturer — typically 20 years. That's on top of our own workmanship guarantee.
We install EPDM as a warm deck system wherever possible, meaning your flat roof meets current Building Regs for insulation. The room below stays warmer, drier, and cheaper to heat.
EPDM has a proven lifespan of 50 years and beyond. The Firestone RubberGard system has been in use since the 1960s, and the earliest installations are still going strong. The manufacturer's guarantee is typically 20 years, but the realistic expectation is well beyond that. It's the most durable domestic flat roofing system available.
A garage roof typically costs £1,200-£2,000. A rear extension roof runs £2,000-£4,000. Per square metre, expect £80-£120 fully installed with insulation. These prices include everything — membrane, insulation, edge trims, adhesives, and labour. The cost is a bit more than felt but a fraction of the cost over the roof's lifetime, since felt needs replacing every 10-15 years.
Both are good systems but they suit different situations. EPDM is better for larger roofs and areas with significant building movement (it stretches rather than cracks). It's also more cost-effective for straightforward rectangular roofs. Fibreglass is better for smaller areas with complex shapes, balconies you'll walk on regularly, and where you want a particular finish colour. We install both and can advise which suits your situation.
In some cases, yes — if the existing covering is flat and firmly adhered, and the deck underneath is sound, we can overlay. But it's often better to strip back to the deck so we can inspect the timber, add insulation, and start with a clean, flat surface. Overlaying an existing roof that's got bumps or soft spots just transfers the problems to the new membrane.
Virtually none. Keep the gutters clear so water drains away, sweep off any heavy debris accumulation, and check the edge trims once a year. That's it. There's no coating to renew, no joints to reseal, no felt to re-bond. It's genuinely fit-and-forget.
We use Celotex or Kingspan PIR (polyisocyanurate) rigid insulation boards, typically 100-120mm thick. These go on top of the deck in a warm deck configuration, which means the structure stays warm and dry and condensation risk is minimised. The insulation thickness is calculated to meet Building Regulations Part L requirements for your specific project.
You can walk on it for occasional maintenance — clearing gutters, checking a TV aerial — without any issues. But EPDM isn't designed as a walkway surface. If you need a flat roof you'll use as a terrace or balcony with regular foot traffic, fibreglass GRP with a non-slip topcoat is the better option. For occasional access, EPDM is absolutely fine.
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