A flat roof in Northampton costs £800–£1,500 for a felt garage roof and £1,800–£4,200 for an EPDM or GRP extension. Per square metre: felt £40–£80, EPDM £80–£120, GRP £95–£140. EPDM lasts 30–50 years and offers the best value. Free surveys on 0160 428 1189.
Flat Roof Cost Northampton · Northampton
Flat Roof Costs by Material and Size
Flat roof cost is driven mainly by two things: the size of the roof and the material. Roofers price flat roofs per square metre, and the material choice is the single biggest variable between a budget felt job and a premium fibreglass finish.
EPDM Rubber: £80–£120/m²
EPDM is the default choice for most Northampton garages, extensions and dormers. It comes in single sheets large enough that a typical extension has no seams at all, it is easily repaired, and it carries a 30–50 year serviceable life. It is the best value over the full lifespan for most properties.
GRP Fibreglass: £95–£140/m²
GRP is laid wet as a resin and glass-fibre laminate then top-coated to a hard seamless finish. It suits balconies, walk-on terraces and roofs where you might later mount solar panels. It needs dry conditions above 5°C to cure, so it is weather-dependent to install.
Felt: £40–£80/m²
Modern torch-on felt is cheapest upfront but shortest-lived at 15–25 years. It is a reasonable choice on a low-value outbuilding but poor value over 40 years because of the replacement cycles.
What the Headline Price Leaves Out
Strip-out and disposal of the old covering adds £300–£700 and is frequently missing from headline quotes. Insulation upgrades to meet building regulations, new decking where the old boards are rotten, and scaffold on a two-storey extension all add cost. Our quotes itemise every one of these so there is no surprise once the old roof comes off.
Local Knowledge
Flat Roofs on Northampton Properties
Flat roofs are everywhere in Northampton's housing stock - on the rear kitchen extensions added to 1930s semis in Kingsthorpe and Abington, on the integral and detached garages of the post-war Blackthorn and Rectory Farm estates, on 1960s–80s Duston estate outbuildings, and on the bay window tops of Victorian and Edwardian terraces in Semilong and Far Cotton.
The most common flat roof job we quote in Northampton is a failed felt garage or extension roof from the 1970s and 80s being replaced in EPDM. A single garage on the Duston estates, around 15m², typically comes in at £900–£1,400 in EPDM including strip-out of the old felt. A rear kitchen extension of 20–25m² on a Kingsthorpe semi runs £1,800–£3,000 depending on material and whether the decking needs replacing.
Bay window flat roofs on the Victorian terraces of Semilong and St James are a distinct job - small, but needing proper lead detailing where the flat meets the wall and the pitched roof above. These typically run £450–£1,200 depending on size, leadwork and access. Where a bay roof sits behind a parapet, drainage detailing matters more and pushes the price toward the upper end.
One local factor worth flagging: many Northampton extension flat roofs from the 1970s and 80s were built with inadequate falls, so water ponds rather than draining. On a replacement we can build in correct falls with tapered insulation, which costs a little more upfront but eliminates the ponding that shortened the life of the original roof. It is the kind of detail a cheap like-for-like replacement skips.
BS 6229, the code of practice for flat roofs with continuously supported flexible waterproof coverings, sets out the minimum 1:80 finished fall required for effective drainage - the detail that prevents the ponding common on older Northampton extension roofs.
Source: BS 6229:2018
Pricing
Flat Roof Prices in Northampton (2026)
Indicative 2026 supply-and-fit guide prices for the Northampton area, including strip-out unless stated. Confirmed in a free written quote after survey.
| Work | Typical Northampton Price |
|---|
| Felt (per m²) | £40–£80 |
| EPDM rubber (per m²) | £80–£120 |
| GRP fibreglass (per m²) | £95–£140 |
| Single garage roof (~15m²), EPDM | £900–£1,400 |
| Rear extension (20–25m²) | £1,800–£3,000 |
| Larger extension (~50m²), EPDM/GRP | £4,500–£8,500 |
| Bay window flat roof | £450–£1,200 |
| Strip-out and disposal | £300–£700 |
Prices are indicative 2026 guide figures for the Northampton area and confirmed in a free written quote after survey. Re-roofing work usually qualifies for the reduced 5% VAT rate.
