How much does a flat roof cost in Swindon? GRP from £800, EPDM from £900.
Flat roof costs in Swindon depend on the area, the system chosen, and the condition of the existing deck. GRP fibreglass and EPDM rubber are the two modern systems we install — both outperform traditional felt by decades. Here are the 2026 prices.
Porch or bay window top (up to 5m²): £800–£1,500. Single garage: £1,200–£2,500. Kitchen or dining room rear extension (10–20m²): £2,500–£5,000. Large extension or dormer (20m²+): £4,000–£8,000. These prices include full strip, deck inspection and replacement where needed, new membrane, edge trims, upstands and our 10-year workmanship guarantee on top of the manufacturer's 25–30 year system warranty.
GRP fibreglass costs approximately 10–15% more than EPDM rubber for the same area. The premium buys you a rigid, seamless, walkable surface that handles foot traffic better than rubber. EPDM is more flexible, easier to install on complex shapes, and slightly cheaper. Both last 25–30+ years. We recommend GRP for areas under 20m² and EPDM for larger areas — the practical differences beyond that are marginal.
Almost every house on Swindon's 1970s–80s estates has a rear extension with an original flat felt roof. These roofs had a 15–20 year design life and they are now 40–50 years old. The felt has cracked, the chipboard deck has swelled from moisture, and the falls were often inadequate from the start. We replace flat roofs in Walcot, Covingham, Eldene, West Swindon and Park North every week. The sheltered valley positions in Walcot and Chiseldon create humidity traps that accelerate felt degradation — flat roofs fail faster here than on the exposed western estates.
Complete strip of existing membrane and deck boarding. Joist inspection and treatment. New 18mm WBP marine-grade plywood deck. Tapered firring strips creating minimum 1:40 falls. Cross-ventilation installation. GRP or EPDM membrane with manufacturer system guarantee. Mechanical edge trims at 200mm centres. Minimum 150mm upstands at all wall junctions. New sealed outlet with leaf guard. Cleanup and guarantee documentation.
BS 6229:2018 (Flat Roofs with Continuously Supported Flexible Waterproof Coverings) specifies a minimum finished fall of 1:40 to prevent ponding. Standing water is the primary cause of premature flat roof membrane failure.
| Porch/bay (up to 5m²) | £800–£1,500 |
| Single garage | £1,200–£2,500 |
| Rear extension (10–20m²) | £2,500–£5,000 |
| Large extension/dormer (20m²+) | £4,000–£8,000 |
| Deck replacement (per m²) | £25–£40 |
| Additional outlet | £80–£120 |
Call 0179 329 7084
0179 329 7084"Kitchen extension flat roof had been leaking for three years despite two patches. They stripped everything, replaced the rotten deck, built proper falls and laid GRP. Three winters later — bone dry. Should have done it years ago."
"EPDM on the double garage. £1,800 including new deck and ventilation. Clean job, two days, 25-year guarantee. The old felt was letting water in every time it rained."
"Small porch flat roof — £950 for full GRP with new deck and edge trims. Done in a day. Looks smart, performs perfectly."
£800–£1,500 for a porch, £1,200–£2,500 for a garage, £2,500–£5,000 for a rear extension. Free quotes with no obligation. Prices reflect the southern England labour band. Conservation area properties in Old Town may cost 20-40% more due to like-for-like material requirements.
GRP fibreglass is seamless, rigid and walkable — ideal for areas under 20m². EPDM rubber is flexible and cost-effective for larger areas. Both carry 25–30 year manufacturer guarantees and massively outperform traditional felt. The cost difference is 10–15%. Choice depends on roof area, access and personal preference. See our GRP vs EPDM comparison.
2–3 days for most Swindon extensions. Single day for porches and garages. Most flat roof failures in Swindon occur on 1970s-80s rear extensions where original felt has exceeded its 15-20 year design life. BS 6229:2018 specifies minimum 1:40 falls for new installations.
If it was traditional felt on chipboard, it had a 15–20 year design life. Most Swindon examples are now 40–50 years old — well past their intended lifespan. Swindon's exposed plateau at 120m means storm damage is more frequent than in sheltered valley towns. Our crews carry the 12 most common tile profiles for same-visit repairs.
10-year written workmanship guarantee on every job covering labour, fixings and installation. Materials carry separate manufacturer warranties. GRP/EPDM: 25-30 years. Concrete tiles: 40-60 years. Natural slate: lifetime. We are NFRC registered with £5m public liability.
We inspect every board individually. Sound plywood is retained. Swollen chipboard — which is extremely common on 1970s-80s Swindon extensions — is always replaced with 18mm WBP marine-grade plywood. The deck condition determines whether boards need replacing, not an arbitrary policy.
Cold roof construction needs cross-ventilation to prevent condensation. We install this as standard on every flat roof replacement. Most flat roof failures in Swindon occur on 1970s-80s rear extensions where original felt has exceeded its 15-20 year design life. BS 6229:2018 specifies minimum 1:40 falls for new installations.
Last reviewed: 2026-08-08
A leaking flat roof that is patched rather than replaced costs more over five years than a replacement. Each patch costs £200–£400 but the underlying felt continues to deteriorate between patches. Water entering through the membrane between patches soaks the deck, saturates the insulation, and eventually causes structural damage to the joists. We regularly strip flat roofs where the chipboard deck has swelled to double its original thickness from years of moisture absorption. At that point, every board must be replaced at £25–£40 per square metre — adding £500–£800 to the replacement cost that would not have been incurred if the roof had been replaced when the membrane first failed. The junction between the flat roof and the house wall is the most common leak point — if your flat roof leak appears at the wall line, the upstand flashing has almost certainly failed and the membrane itself may be close behind.
GRP fibreglass: seamless single-piece layup with no joints. Rigid when cured — walkable for maintenance access. Resin topcoat provides UV protection and a clean finish. Ideal for areas under 20m² where the seamless property is most valuable. Manufacturer guarantee: 25–30 years (Topseal, Cure It). EPDM rubber: large sheets bonded to the deck with adhesive. Flexible — accommodates minor structural movement without cracking. Lighter weight than GRP. Better for larger areas where GRP layup becomes impractical in a single session. Manufacturer guarantee: 20–25 years (Firestone, ClassicBond). Both systems massively outperform traditional felt, which has a 10–20 year lifespan versus 25–30+ for modern systems. The cost difference between GRP and EPDM is typically 10–15% — not enough to drive the decision. Choose based on area size, access needs and personal preference.
A well-installed modern flat roof needs minimal maintenance but benefits from annual attention. Clear debris from around outlets and upstands every autumn. Check for ponding after heavy rain — water should drain within 24 hours. Inspect edges and upstands for any lifting or separation. For GRP, avoid dragging heavy objects across the surface. For EPDM, keep solvents and oils away from the membrane. Do not pressure wash either system. These simple checks take 15 minutes and can identify minor issues before they develop into problems that threaten the guarantee.
Twenty years of continuous service to Swindon homeowners means we have fixed roofs on every type of property in every neighbourhood. We have seen every roofing problem this town produces — from the nail sickness crisis on the post-war estates to the listed building conservation work in Old Town and the Railway Village. We know which materials last in Swindon's exposed conditions and which fail prematurely. We have a reputation built entirely on doing good work at fair prices — no advertising, no cold calling, just honest workmanship that speaks for itself. We are NFRC registered, carry five million pounds of public liability insurance, and provide a written 10-year workmanship guarantee on every job. We do not subcontract and we do not employ commission-based salespeople. Our own experienced team handles every project from the initial survey through to completion and sign-off. Call 0179 329 7084 for a free, no-obligation survey and quote.
From £150, no call-out fee.
More →Full re-roofs, 10yr guarantee.
More →GRP/EPDM, 25yr guarantees.
More →Same-day 24/7 response.
Call Now →Cleaning, repairs, replacement.
More →Repointing, flashings, stacks.
More →Biocide, 3-5yr protection.
More →uPVC roofline, ventilation.
More →Fitted to your roof.
More →Code 4 flashings, valleys.
More →Repair, matching, re-roofing.
More →Surveys from £120, fee credited.
More →Here is how to tell if you need this service — and when you might not.
When it is not the answer: If the problem is minor and localised, a targeted repair may be more cost-effective. We assess honestly during the free survey.
We inspect the relevant roof area, photograph everything, and explain what needs doing.
Itemised specification with materials, labour and access costs clearly separated.
Our own team carries out the work to specification. Daily cleanup, weathertight each night.
Walk-through, 10-year guarantee issued, site cleared.
| Job | Typical duration |
|---|---|
| Minor work | Half day - 1 day |
| Standard job | 1-3 days |
| Complex / large scope | 3-5 days |
Weather dependent — we never compromise quality for speed.
Access method depends on the specific job — ladder, tower scaffold or full scaffold. Always itemised in your quote. Scaffold is specified for: work above single-storey height, multi-day jobs, chimney and ridge access — always itemised in your written quote, never a hidden extra.
Pavement scaffold and skip permits go through Swindon Borough Council. On restricted streets in Old Town, the Railway Village and parts of Rodbourne, we coordinate access to minimise disruption. Allow a few working days for permit processing.
All work carries our written 10-year workmanship guarantee. Materials carry separate manufacturer warranties on top.
If a fault appears in covered work, we come back and put it right. No quibbling, no re-charge.
External work during standard hours. We sheet below and clean up each day. You do not need to be home. You do not need to stay home for external work — we just need access agreed in advance.
Work runs year-round where conditions allow. We build weather margin into every schedule and never leave a roof exposed. Swindon's exposed plateau at 120m produces more frost days and stronger gusts than sheltered valley towns — we factor this into every schedule.
Trusted Swindon roofers. Call 0179 329 7084.
0179 329 7084