Fibreglass Garage Roof Cost & Kit Guide (UK)

Garage sizes and what they cost

A typical single garage is around 6 m × 2.5–3 m — call it 15–18 m². A double runs around 6 m × 5–6 m, so 30–36 m². Those numbers drive everything: at 600g spec you need 1.5 kg/m² of resin, 0.72 kg/m² of topcoat and 0.6 kg/m² of matting plus cutting waste.

A 15 m² single garage lands around £600–650 in complete materials: roughly £204 of resin (2 × 20 kg tubs), £108–156 of topcoat (1 tub), £78 of matting (~10 kg), £50 of catalyst (5 kg pack), £33 of acetone (5 L), and £110–125 of trims plus adhesive and bandage.

A 33 m² double roughly doubles the laminate but not the perimeter: about 50 kg resin (3 tubs), 24 kg topcoat (2 tubs), ~22 kg matting, and a longer trim run — expect £1,100–1,250 in materials. Compare either figure with fitted quotes of £80–110+ per m² and the DIY saving is obvious.

Which tier for a garage?

Protect (600g laminate) is the right answer for almost every garage — it's the standard domestic spec, comfortably takes the occasional foot traffic of gutter cleaning and aerial fiddling, and it's our most popular system by a distance.

Essential (450g) is a legitimate saving on a light prefab or sectional concrete garage where nobody will ever walk and the structure itself has a limited life. It cuts resin use to about 1.2 kg/m², saving a tub on many singles.

Premier (600g with fire-retardant CrysticROOF topcoat) earns its premium when the garage sits on a boundary — fire performance close to neighbouring property is increasingly what building control ask about — or when the roof doubles as a terrace, where the optional anti-slip finish matters.

The deck: where garage jobs are won

Almost every garage re-roof starts with overboarding or replacing the deck. GRP needs dry, rigid, clean board — the standard is 18 mm OSB3 tongue-and-groove, screwed at about 200 mm centres. Laminating over old felt, chipboard, or springy 12 mm ply is how GRP gets an undeserved bad name.

Check the fall while you're up there: 1:80 minimum towards the gutter edge, ideally 1:40. Garage roofs are often dead flat and pond; firring strips under the new deck fix it cheaply at this stage and never again.

Concrete-panel garage roofs are a different conversation — GRP wants a timber deck, so budget for timber bearers and boarding over the panels, or reconsider the system.

Trims for a typical garage

The standard garage layout: A200 drip trim along the low (gutter) edge, B230 raised edge along both sides, and either another A200/B230 or a D260 wall fillet plus C100 cover flashing at the back depending on whether the garage stands free or abuts the house.

For a 6 m × 2.5 m single: two 3 m A200s, two 3 m B230s per side (four total), and the rear edge's pair — eight to ten 3 m lengths at around £13–16 each, plus corner units at each junction, adhesive and bandage.

Attached garages need care where the roof meets the house wall: that's the D260 + C100 detail, with the cover flashing chased into a mortar joint. It's the one detail worth studying twice before you start.

Is a garage a realistic first GRP job?

Yes — it's the ideal one. Low, rectangular, small enough for one day, big enough to matter. Two people, a dry day between 5 and 30°C, all materials cut and staged the day before, and the catalyst table taped to the resin tub.

The realistic schedule: deck work one weekend, then trims, bandage, laminate and topcoat on the next dry day. Laminating a single garage takes 3–4 hours; the topcoat under an hour.

Read our step-by-step guide before you order, and be honest about the weather window — the material costs the same on a good day as a bad one, but only one of them gives you a 25-year roof.

Frequently asked questions