Flat roofs on extensions, garages, and outbuildings across Aylesbury are failing at scale — particularly on the post-war estates where felt roofs have reached the end of their serviceable life. We replace them with GRP fibreglass or EPDM rubber systems that carry a 20–25 year warranty.
Across Southcourt, Quarrendon and other post-war areas of Aylesbury, the rear kitchen and bathroom extensions built in the 1950s, 1960s and 1970s were covered with three-layer felt flat roofs. These systems have a design life of 15–20 years. Many of them are now 40–50 years old and well beyond serviceable condition. Blistering, splitting at seams, ponding water, and complete felt breakdown are the patterns we see repeatedly on this housing stock.
The right replacement system depends on the use of the roof, the deck condition, and any falls that need correcting. GRP fibreglass is our most popular choice for residential extensions: it lays as a single seamless membrane with no joints to fail, takes foot traffic, looks clean and tidy, and carries a manufacturer-backed 25-year product warranty when correctly installed. EPDM rubber is an excellent alternative where budget is a priority or where the deck has minor movement — it is flexible, durable, and performs well on both warm and cold roof constructions.
Single garage flat roof (standard 3x5m): £900–£1,600. Single-storey extension 20–30m²: £1,800–£3,500. Larger extension or flat-roof dormer: £3,500–£6,000+. Costs depend on deck condition, system choice, and drainage requirements. All surveys and quotes are free.
GRP fibreglass flat roofs are trafficable and can accommodate occasional foot access for maintenance. EPDM and felt systems are not designed for regular foot traffic. Where regular access is needed — for a roof terrace or to access plant — we can specify and install a suitable protection layer or paving system as part of the job.
Need a quote today? Our team covers all of Aylesbury and the surrounding area.
Call 0129 670 6028Flat roofs fail differently from pitched ones. Here is how to tell whether yours needs replacing — and whether the deck is the real problem.
When it is not the answer: If the failure is a localised split on an otherwise sound roof with a dry deck, a repair — not a full replacement — is the honest fix. We prove the deck condition before recommending either. Read the full guide.
We probe the deck at multiple points for moisture and check the falls, then show you the readings and the honest repair-or-replace picture.
GRP or EPDM specified to suit the roof, with any deck replacement shown as a clear contingency, not a surprise.
Most single garages and extensions are booked and completed inside a day or two.
Old covering stripped, deck made good, GRP or EPDM installed with perimeter and outlet detailing.
Site cleared; 25-year manufacturer warranty and 10-year workmanship guarantee issued in writing.
| Job | Typical duration |
|---|---|
| Single garage, GRP | 1 day |
| Rear extension, GRP | 1–2 days |
| Large flat roof, EPDM | 2–3 days |
| With deck replacement | add 1 day |
GRP needs dry, above-minimum temperatures to cure, so cold or wet spells can push a booking — EPDM is more weather-tolerant.
Most flat roofs are single-storey and reached from a tower; scaffold is quoted only where the roof is high or awkward. Scaffold is specified for: first-floor and higher flat roofs, or where safe edge protection is needed - always itemised in your written quote, never a hidden extra, and we arrange it.
Aylesbury's mix runs from post-war and 1970s estate semis on Bedgrove, Southcourt and Quarrendon — open-access, straightforward scaffold — to the tight lanes of the Old Town conservation area and the village cores of Long Crendon and Bierton, where pavement space is limited and scaffold needs planning. Pavement scaffold and skip permits go through Buckinghamshire Council; allow a few working days on streets like Church Street, Parson's Fee, Temple Street where space is tight.
| Job | Typical range | Notes |
|---|---|---|
| Single garage, GRP | £1,400–£2,200 | 16–18m² |
| Rear extension, GRP | £2,000–£3,500 | 20–30m² |
| Large flat roof, EPDM | £3,000–£5,000 | 30–50m² |
| Deck replacement, if needed | £40–£70/m² | Where saturated |
| Insulation upgrade | £400–£1,200 | Building Regs thermal element |
Worked example: A GRP re-cover on a Bedgrove rear extension with a sound deck runs about £2,600, completed in a day and a half.
No deposit on repairs under £500; staged payment on full replacements, nothing before materials on site. VAT included.
Covering HP17, HP18, HP19, HP20, HP21, HP22 and surrounding postcodes.
Both GRP and EPDM carry 25-year manufacturer warranties, with our 10-year workmanship guarantee on top of the installation.
If a fault appears in covered work, we come back and put it right. No quibbling, no re-charge.
A day or two of work over a garage or extension, largely external — minimal disruption to the house. You do not need to stay home for external work - we just need power and access agreed in advance.
GRP is temperature and moisture sensitive during cure; we schedule around the forecast. EPDM can be laid in a wider weather window. The Vale of Aylesbury sits open to the prevailing south-westerly weather across flat farmland, and the low-lying clay around Southcourt holds damp longer in autumn, slowing drying times.
"Flat roof on our rear extension in Southcourt had been letting water in for two years. Got a GRP replacement and it looks completely different β clean, solid and warm. The team were tidy and finished in one day."
"Garage flat roof was a complete write-off β felt had split along every seam. New EPDM system went on in a morning. Four years later and still perfect β not a drop of water."
"Did a full survey including falls assessment and deck condition check before quoting. Found one section of decking that needed replacing and told us upfront. Very honest and the GRP finish is flawless."
We cover Aylesbury and a 15-mile radius. Click your town for local pricing, housing-specific advice, and availability.
We cover Aylesbury and a 15-mile radius. Click your town for local pricing, housing-specific advice, and availability.
A correctly installed GRP fibreglass flat roof carries a 25-year product warranty and a practical lifespan of 30β40 years with minimal maintenance. The Vale of Aylesbury climate is not unusually harsh for flat roofing, but ensuring correct falls and drainage is critical β ponding water accelerates degradation on any system.
If the roof is less than 15 years old and the deck is sound, a targeted repair is usually viable. If the felt is cracked, blistered or delaminating across more than 30% of the surface, a full replacement is more cost-effective. We assess the deck condition and falls during our free survey and give you an honest recommendation.
In most cases, replacing a flat roof like-for-like is permitted development and does not require planning permission. If you are changing the height or altering the footprint, permission may be needed. Properties in conservation areas around Aylesbury town centre may have additional restrictions β we check during the survey.
The original three-layer built-up felt systems used on 1950sβ1970s Southcourt and Quarrendon extensions had a design life of 15β20 years. UV degradation, thermal movement, and water ingress at seams cause gradual breakdown. Blocked outlets that allow standing water accelerate failure significantly. By the time most of these roofs reach 40β50 years, they are well beyond economic repair.
A standard rear extension of 10β20mΒ² typically takes one full working day for a GRP installation β preparation and priming on day one if the deck needs drying, lay-up and topcoat on day two. Larger roofs or those requiring deck replacement take longer. We give you a realistic programme in the quote and never leave a flat roof open overnight.
Technically yes β GRP and EPDM are both walkable surfaces when specified to the correct standard. Whether it's permitted development or needs planning permission depends on the extension size, your property type, and whether it overlooks neighbouring gardens. We'd always recommend a Pre-Application Enquiry with Buckinghamshire Council before designing a roof terrace on an existing extension.
The three most common causes are: deck saturation before installation (damp OSB that swells and moves under the new membrane); poor edge and upstand detailing (water tracks behind the membrane at perimeter joints); and using the wrong system for the thermal movement profile of the building. Our GRP installations are primed and laid in one continuous operation to avoid deck exposure, and all edge details are formed in fibreglass rather than cut and sealed.
No call-out fees. No obligation. Just an honest quote from a local Aylesbury roofer.
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