Question 1

How much does a fibreglass roof cost in Ireland?

Accepted Answer

A GRP flat roof on a garage or extension costs €2,800 to €6,500, and €3,800 to €6,500 on a 30 to 40 m² kitchen extension. Laid, GRP runs €75 to €140 a m². The cost guide breaks it down.

Question 2

Is GRP the same as fibreglass?

Accepted Answer

Yes. GRP is glass-reinforced polyester: glass fibre mat set in resin and finished with a coloured topcoat. Roofers use both names for the same roof.

Question 3

How long does a fibreglass roof last?

Accepted Answer

25 to 35 years when it's laid on a sound deck in dry weather. See how long it lasts .

Question 4

Can GRP go over my old felt roof?

Accepted Answer

Sometimes, if the deck underneath is dry and sound: €1,800 to €5,000. See GRP over an existing roof .

Question 5

What if it rains on the day?

Accepted Answer

Nothing goes down in the wet: GRP laid on a damp deck fails. A good roofer keeps a sheet on site, stops, covers the roof and comes back on the next dry day.

Question 6

Will there be a smell?

Accepted Answer

Yes, while the resin and topcoat cure, for a day or so. Keep windows near the roof shut while it's laid; it goes once the roof has cured.

Question 7

What guarantee do I get?

Accepted Answer

Ask for two in writing: the roofer's workmanship guarantee (10 years is common for a good one) and the material guarantee on the GRP system (often 20 to 25 years).

Question 8

Who comes out to look at the roof?

Accepted Answer

One flat roofing company that covers your county. One company only, not a list.

Question 9

Why must fibreglass roofing be laid on OSB3 boards rather than marine plywood?

Accepted Answer

OSB3 tongue-and-groove sterling board has an open wood-strand surface that absorbs catalysed polyester resin deeply, locking the GRP laminate into the timber. Plywood has dense glue lines and smooth face veneers that can delaminate from rigid resin under summer heat.

Question 10

Does a fibreglass flat roof expand or make clicking noises in hot weather?

Accepted Answer

A properly consolidated GRP roof laid on 18mm T&G OSB3 with a 25mm perimeter expansion gap at abutment walls moves quietly as a single unit. Clicking noises usually happen only when thin boards were under-fixed with smooth nails instead of ring-shank nails or decking screws.

Question 11

Can you walk on a GRP fibreglass flat roof or use it as a balcony?

Accepted Answer

Yes. Standard 450g/m2 GRP handles normal maintenance foot traffic for window cleaning or chimney access, while daily-use balconies and terraces are upgraded to 600g/m2 or double-layer 450g/m2 laminate with a quartz non-slip gritted topcoat.

Question 12

What weather conditions are needed on the day a GRP roof is laid?

Accepted Answer

The OSB3 deck must be bone dry and air temperature must sit between 5C and 30C with no rain until the resin and topcoat cure (typically 45 to 90 minutes per coat). On damp Irish days, the roofer strips and prepares in stages under temporary weather cover.

Question 13

How easy is it to repair or extend a GRP fibreglass roof years later?

Accepted Answer

Very straightforward: the existing grey topcoat is sanded back to raw laminate with 40-grit abrasive paper, wiped clean with acetone, and new resin, chopped strand mat and topcoat are chemically bonded directly onto the original layer.

Question 14

What colour is a standard fibreglass flat roof finished in?

Accepted Answer

Over 90% of Irish domestic GRP roofs are finished in dark slate grey (RAL 7015) or lead grey (RAL 7043) to match natural slate and uPVC guttering, though any BS or RAL pigment can be mixed into the topcoat.

Question 15

Which counties do you cover?

Accepted Answer

All 26. Each request goes to one flat roofing company that covers your county. If no company covers you, we'll tell you straight.

Question 16

Are GRP prices different by county?

Accepted Answer

Yes. Dublin runs 15 to 25% above rural prices and the commuter belt 5 to 15% above.

Question 17

Where are flat main roofs most common?

Accepted Answer

Dublin has the highest share of houses with a flat main roof, 3.0%, and Cavan the lowest, 0.8%.

Question 18

Is GRP good for a balcony?

Accepted Answer

It's the usual choice, with the heavier mat and an anti-slip topcoat.

Question 19

What does a dormer roof in GRP cost?

Accepted Answer

A small GRP roof is €2,800 to €6,000. Scaffolding or a tower at height adds to it.

Question 20

Can a balcony over a room be GRP?

Accepted Answer

Yes, if the build-up under it is right: falls, insulation if the room is heated, and a proper threshold detail. That's one for the roofer to look at.

Question 21

How much is a GRP roof on an extension?

Accepted Answer

€3,800 to €6,500 for 30 to 40 m²; €6,000 to €9,500+ as a warm roof over a heated room.

Question 22

Should I insulate when the roof is replaced?

Accepted Answer

Over a heated room, usually yes: it's the one time the deck is open.

Question 23

How big can an extension be without planning?

Accepted Answer

45 m² at the rear under the 2026 regulations, with conditions.

Question 24

Is GRP good for a garage roof?

Accepted Answer

Yes. It has no seams, takes foot traffic for gutter cleaning, and suits a small plain roof. EPDM and felt are the lower-cost options.

Question 25

How long does a garage roof take?

Accepted Answer

Often a day or two in dry weather.

Question 26

Do I need planning to re-roof my garage?

Accepted Answer

Not to re-cover it the same way. Raising it or changing to a pitched roof is a question for the council.

Question 27

Is GRP dearer than EPDM?

Accepted Answer

A little: GRP is €75 to €140 a m² laid, EPDM €70 to €140 a m²; a whole GRP roof €2,800 to €6,500 against €2,500 to €5,800 in EPDM.

Question 28

Why do GRP prices vary so much?

Accepted Answer

Size, the state of the deck, insulation, access and the number of details: trims, upstands, outlets, rooflights. A small dormer with three walls round it can cost more a m² than an open garage.

Question 29

Is a cheaper quote missing something?

Accepted Answer

Often the new deck, the trims, the skip or VAT. Ask for every item in writing, so you compare the same job.

Question 30

Does GRP roofing carry 23% VAT?

Accepted Answer

No. Roofing work on a house is at the 13.5% rate.

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