Barnet at a glance
- Postcode districts
- N20, N11, N14, N12, EN4, N3, EN5, NW7 and 1 more
- Council area
- London Borough of Barnet
- Building approval
- London Borough of Barnet building control, or a registered building control approver
- Guide price region
- London (+20% on West Midlands rates)
Why choose GRP fibreglass roofing in Barnet?
GRP is a good fit in Barnet for roofs with awkward shapes, short runs of upstand and lots of corners, because every detail is laminated in place rather than cut and glued. Where a sheet membrane would need many joins, fibreglass forms one continuous skin across the whole roof.
Around Barnet, flat roofs are common on Victorian and Edwardian terraces with flat-roofed back additions and on mansion blocks and purpose-built flats with large flat roofs. The Thames basin is one of the drier parts of Britain at roughly 730 mm of rain a year, but summer heat is the bigger test here: dark membranes on south-facing roofs swing a long way in temperature.
How much does a GRP fibreglass roof cost in Barnet?
Guide price in Barnet: £3,600–£6,450 for a 20 m² extension roof in GRP with a new deck and insulation, including VAT at London rates. The fixed price comes after a free survey for new and replacement roofs.
| Job | Guide price inc VAT |
|---|---|
| Extension (20 m²), GRP, new deck + insulation | £3,600–£6,450 |
| Dormer (8 m²), GRP, scaffold | £1,700–£3,200 |
| Single garage (18 m²), GRP fibreglass | £2,150–£3,900 |
| Single garage (18 m²), EPDM rubber | £1,900–£3,350 |
| Extension (20 m²), EPDM, new deck + insulation | £3,350–£5,850 |
Why do GRP roofs crack, and can weather affect the installation?
GRP usually cracks where the structure moves and the laminate cannot, typically along board joints, at the junction with trims, or where a roof meets a wall. Weather during laying is the other big factor, because resin cures by chemical reaction and that reaction is sensitive to temperature and moisture.
How we reduce the risk of cracking:
- boards fixed at close centres so the deck does not flex;
- joints taped and reinforced with an extra strip of mat;
- wall junctions finished with a separate trim or flashing, not laminated hard into the masonry;
- roofs over a certain size divided with movement details where the system calls for them.
And how weather is managed:
- no laminating in rain, on a damp deck, or when dew or frost is likely before the resin sets;
- catalyst levels adjusted for the temperature, so resin neither stays tacky on a cold day nor kicks too fast in summer heat;
- the roof sheeted over if a shower threatens a fresh laminate.
That is why a GRP date can move at short notice. A day's delay costs far less than a laminate that never cures properly.
What's included?
- Removal of the old covering and disposal of waste
- Coloured UV-stable topcoat, with anti-slip finish on request
- New OSB3 or plywood deck, fixed at close centres
- Moulded GRP trims, kerbs and upstands
Building regulations in England
Replacing more than half of a flat roof over a heated room usually counts as renovating a thermal element, so the roof is insulated to around 0.16 W/m²K where that's technically and economically feasible, and the work is notified to building control: the council or a registered building control approver, unless a registered competent person self-certifies it. A roof on a new extension is built to 0.15 W/m²K. Patch repairs, and most unheated detached garages, don't trigger the upgrade. Structural changes, or a new covering that adds 15% or more to the roof's weight, also need approval. More on the rules.
Which nearby areas do we also cover?
GRP fibreglass roofing in Barnet: questions
Do you cover Barnet?
Yes. Barnet is part of our London coverage, including postcode districts N20, N11, N14, N12, EN4, N3 and 3 more. Surveys and roofs are carried out by vetted roofing teams working under S&K Property Investments and Improvement Ltd.
Who checks building regulations for a flat roof in Barnet?
Where the work needs approval it goes to London Borough of Barnet building control, or a registered building control approver. We tell you at the survey whether your job needs it and deal with the paperwork as part of the quote.
How much does a GRP fibreglass roof cost in Barnet?
£3,600–£6,450 for a 20 m² extension roof in GRP with a new deck and insulation, at London guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
Can GRP be laid over an existing felt roof?
Generally no. GRP needs a clean, dry, rigid timber deck, so the old felt is usually stripped and the boards replaced before laminating.
Does GRP smell when it is being laid?
Yes, the resin gives off a strong styrene smell while it cures. It usually fades within a day or so, and we advise keeping nearby windows closed while the team works.