In 40 seconds
Replacing a small flat roof such as a garage or single-storey extension typically costs around £1,000–£3,000 in the UK, with the price set mostly by the area and the covering. By material, installed prices run roughly £80–£120 per m² for EPDM rubber, £90–£130 per m² for GRP fibreglass, and £40–£70 per m² for felt. They also last for different lengths of time: a well-fitted EPDM roof lasts about 20–30 years, GRP fibreglass about 20–25 years, and felt about 10–15 years. Most replacements today are built as a warm deck, with insulation above the structure to meet building regulations. The honest answer is always a range, because it depends on your roof size, the covering and access.
Most flat-roofing guidance is published by firms fitting it, so the numbers tend to be optimistic and the trade-offs glossed over. The pages below give honest cost ranges for flat roofs only — garages, extensions and dormers — compare EPDM, GRP and felt fairly, explain how long each lasts, and cover the warm-deck basics, before you take a single quote.