Flat roofs over extensions, garages and dormers are where a large share of our leak call-outs come from, and the first question is always the same: what is this going to cost? The honest answer is that it depends far more on what is under the surface than on the crack you can see. But you should not have to ring a roofer completely blind, so here are the figures we work with across Kerry, Cork and Limerick in 2026, and what pushes a price up or down.
The short answer
Most flat roof repairs in Ireland fall into three bands:
- A localised repair to a crack, blister, split joint or lifted edge trim usually costs EUR 250 to EUR 900.
- Re-covering a small roof, such as a 20 to 30 square metre extension in new fibreglass (GRP), is typically EUR 2,000 to EUR 5,500, depending on the state of the deck.
- A new flat roof runs at roughly EUR 70 to EUR 140 per square metre depending on the system, the deck and the insulation, with access on top where it is needed.
Those ranges are wide for a reason. Two extensions on the same estate can be thousands apart once the old covering comes up and the deck underneath is either sound or soaked.
Typical flat roof repair prices in 2026
| Job | Typical cost | Notes |
|---|---|---|
| Crack, blister or split joint repaired | EUR 250 to 900 | Cut out, rebonded and sealed on a sound, dry deck |
| Edge trim or upstand detail redone | EUR 250 to 900 | Where most flat roofs actually fail |
| Skylight dome replaced on existing upstand | EUR 450 to 1,000 | Depends on dome size; upstand repairs priced separately |
| Emergency temporary cover | EUR 300 to 800 | Keeps the weather out until a proper repair can be done |
| Small roof re-covered in GRP (20 to 30 m2) | EUR 2,000 to 5,500 | Includes new deck where needed |
| New flat roof, per square metre | EUR 70 to 140 | System, deck and insulation decide where in the range |
These are guide figures for the south west, not quotes. Nobody can price a flat roof properly without standing on it and, ideally, lifting a corner to see the deck.
What decides the price
The deck underneath
This is the single biggest swing. A flat roof is only as good as the boards it sits on. If water has been getting in for a while, chipboard swells and crumbles, ply delaminates, and insulation turns into a sponge. A covering laid over a wet or soft deck fails with it, so the rotten section has to come out first. A repair that would have been a few hundred euro on a dry deck becomes a strip-out and re-deck if the leak has been left a few winters.
Upstands, outlets and rooflights
The middle of a flat roof almost never fails. The edges do: where the roof meets a wall, the gutter trim, the outlet and any rooflight or pipe coming through. A plain rectangle with one outlet is quick. A roof with a skylight, a soil vent, a parapet and two outlets has far more detail to get right, and that time is in the price.
The system
Fibreglass, liquid systems such as Lava 20, EPDM rubber and torch-on felt all cost different amounts and suit different roofs. See the next section.
Insulation
If anything habitable is underneath, re-covering is the time to bring the roof up to a proper warm deck, with insulation over the joists. It adds to the price on the day and pays back in heating and in a roof that does not suffer from condensation. See roof insulation.
Access, waste and weather
A single-storey extension off the back garden is straightforward. A dormer on the second floor needs proper access, and that is a real line on the quote. Strip-out means a skip or waste removal. And resin systems need a dry deck and the right temperature to cure, so winter jobs are booked around the forecast.
Cost by flat roof system
| System | Fitted price guide | Typical life |
|---|---|---|
| Fibreglass GRP | EUR 90 to 140 per m2 including a new deck | 25 to 30 years |
| Lava 20 liquid system | EUR 80 to 130 per m2, less with no strip-out | 20 to 30 years |
| EPDM rubber | Within the EUR 70 to 130 per m2 range for most roofs | 30 to 50 years |
| Torch-on felt | Within the EUR 70 to 130 per m2 range for most roofs | 15 to 25 years |
The cheapest system on the day is not always the cheapest over the life of the roof. GRP needs a new ply deck because it will not bond over felt or chipboard, which puts it at the top of the range, but it gives a seamless, walkable finish. A liquid system like Lava 20 can often go over the existing covering if it is sound and dry, which saves the strip-out. Our flat roofs page compares them in more detail.
Repair, overlay or replace?
Repair makes sense when the leak is in one place, the rest of the covering is in reasonable order and the deck is dry and firm. Most flat roof call-outs end here, and our fibreglass flat roof repair page explains how we bond a repair into an older GRP roof.
Overlay with a liquid system makes sense when the old covering is tired all over, there are several small leaks, but the deck and insulation underneath are still sound and dry.
Replace when the deck is soft in more than one spot, the insulation is wet, the roof holds standing water because the fall has gone, or it has already been patched several times. At that point every repair is money spent chasing the next leak.
Signs a flat roof is past repairing:
- The roof feels spongy or gives underfoot
- Puddles still sitting two days after rain
- Leaks in more than one place, or moving around
- Cracks and crazing across the whole surface, not just at the edges
- Stains on the ceiling below spreading even in dry spells
Cheap fixes that cost more later
- Bitumen paint or sealant over the crack. It may stop a drip for a season, but it hides the problem while the deck keeps getting wetter underneath.
- A new covering over a wet deck. Water trapped under a new membrane has nowhere to go. The new roof blisters and fails with the old one.
- Felt or GRP laid straight on chipboard. Chipboard swells the first time it gets wet. Flat roof decks should be exterior-grade ply.
- Ignoring the fall. A flat roof is never truly flat. If water is ponding, the fall needs to be built back in, or any new covering will be sitting in a puddle.
How to compare flat roof quotes
A one-line quote with one number on it is not a quote. A proper one should spell out:
- whether the old covering is being stripped or overlaid
- how much of the deck is being replaced, or how unexpected rot will be priced if it is found
- upstands, trims, outlets and any rooflight
- insulation, if any, and its thickness
- access, skip and waste removal
- whether VAT is included (construction work is charged at 13.5% where the contractor is VAT-registered)
- what the guarantee covers and for how long, in writing, and whether there is a manufacturer guarantee on the system as well
Be wary of a price well below the others. It usually means the deck has not been allowed for, and it comes back as an extra once the old roof is off.
Flat roof repair cost: questions we get asked
How much does it cost to repair a flat roof in Ireland?
A localised repair to a crack, blister, joint or edge trim usually costs EUR 250 to EUR 900. Re-covering a 20 to 30 square metre roof is typically EUR 2,000 to EUR 5,500, and a new flat roof runs at roughly EUR 70 to EUR 140 per square metre depending on the system, deck and insulation.
Is it cheaper to repair or replace a flat roof?
If the leak is in one place and the deck is dry and firm, a repair is far cheaper and the right call. Once the deck is soft, the insulation is wet or the roof has been patched several times, replacement usually works out cheaper than paying for repair after repair.
Can you put a new flat roof over the old one?
Sometimes. A liquid system such as Lava 20 can go over existing felt or GRP if what is underneath is sound and completely dry. Fibreglass GRP cannot: it needs a new ply deck. A new covering over a wet deck will fail, so the deck always gets checked first.
Can a flat roof be repaired in winter?
Yes, but resin-based repairs need a dry surface and temperatures above about 5 degrees to cure, so we book them around the forecast. In the meantime a temporary cover can keep the weather out.
How long does a flat roof repair last?
A repair bonded into a sound roof should last as long as the rest of the covering around it. A repair on an old roof that is failing all over buys time rather than solving the problem, and we will tell you which one yours is.
Get a real price for your flat roof
Everything above is a planning range. To get a figure you can rely on, send us a photo of the roof and the stain inside on WhatsApp, or ring 085 220 1422. We survey free across Kerry, Cork and Limerick, check the deck, and give you a fixed written price with a written guarantee. If the roof is leaking right now, read what to do when a roof leaks in heavy rain first, or get in touch here.