How Much Does a GRP Fibreglass Roof Cost? (UK Guide)

What you're actually paying for

A GRP roof is built up in layers on a dry timber deck: catalysed polyester resin with chopped strand matting (CSM) bedded into it, cured, then finished with a pigmented topcoat. The materials that scale with roof area are resin, matting, topcoat, catalyst and acetone for tool cleaning. The materials that scale with the perimeter are the edge trims, trim adhesive and jointing bandage.

The coverage rates are well established. A 600g CSM laminate takes about 1.5 kg of resin per m². Topcoat goes on at about 0.72 kg per m². The matting itself weighs what it says — 600g/m² matting is 0.6 kg per m², plus roughly 10% for cutting waste. Catalyst is dosed at 1–4% of the combined resin and topcoat weight depending on air temperature, and you'll use around 0.1 litres of acetone per m² keeping rollers and brushes workable.

Trims are the bit people forget to price. Every edge of the roof needs the right profile — a drip trim into the gutter, raised edge trims on the verges, wall fillets where the roof meets brickwork — and they're sold in 3 m lengths at around £13–16 each. On a small roof the trims can be 15–20% of the bill.

Materials cost per square metre

Working from live shop prices (all inc VAT): resin is around £102 for a 20 kg tub (about £5.10/kg), standard topcoat around £108–156 for 20 kg depending on grade, 600g matting around £7.80/kg, catalyst around £50.40 for 5 kg, and acetone around £33 for 5 litres.

Per square metre that works out at roughly: £7.65 of resin (1.5 kg), £3.90–5.60 of topcoat (0.72 kg), £4.70–5.20 of matting (0.6 kg plus waste), under 50p of catalyst and about 65p of acetone. Call it £17–20 per m² for the laminate itself, before trims and sundries.

The honest caveat: materials come in fixed pack sizes. Resin and topcoat are 20 kg tubs, catalyst is 5 kg or 25 kg, acetone 5 L or 25 L. A 15 m² roof needs 22.5 kg of resin, so you buy two tubs and carry spare. The smaller the roof, the more pack rounding inflates the per-m² figure — which is exactly why a per-m² price on its own is misleading.

Worked example: a 15 m² garage roof

Take a 6 m × 2.5 m single garage (15 m², 17 m perimeter) on our Protect tier (600g laminate, the most popular spec). Resin: 15 × 1.5 = 22.5 kg → 2 × 20 kg tubs, around £204. Topcoat: 15 × 0.72 = 10.8 kg → 1 × 20 kg tub, around £108–156. Matting: 15 × 0.6 kg plus waste ≈ 10 kg, around £78. Catalyst: (22.5 + 10.8) kg × 2% ≈ 0.7 kg → the 5 kg pack, around £50. Acetone: 1.5 L needed → 5 L bottle, around £33.

Trims for that roof: say a 6 m gutter edge (2 × A200 drip), two 2.5 m verges (2 × B230 raised edge) and a 6 m wall fillet at the back (2 × D260 plus 2 × C100 cover flashing). Eight 3 m lengths at £13–16 each is roughly £110–125, plus trim adhesive and jointing bandage.

All in, that garage lands around £600–650 in materials. That's the realistic DIY number — about £40–43/m² on a roof this size once pack rounding and trims are counted. A contractor supplying and fitting the same roof will typically quote £80–110+ per m², so doing the laying yourself roughly halves the cost.

What pushes the price up or down

Spec matters. Our Essential tier uses 450g matting (about 1.2 kg/m² of resin), which trims the materials bill and is fine for sheds and garden buildings. Premier tier adds a fire-retardant CrysticROOF topcoat and optional anti-slip — worth it near boundaries or on balconies, and it's why the topcoat range runs from around £108 up to around £156 per tub.

Complexity costs more than area. Skylights and upstands need extra bandaging and detailing. An L-shaped roof has more perimeter per m² than a simple rectangle, so more trims. And if the existing deck is rotten, new 18 mm OSB3 tongue-and-groove boarding is a separate line on the bill entirely.

Delivery is the last variable: resin, topcoat, catalyst and acetone are classed as hazardous goods and travel on a specialist ADR courier network, priced by postcode at checkout. Collection from our Boston, Lincolnshire depot is free.

Frequently asked questions