Overlays
Fibreglass Over an Existing Roof
Sometimes. A new GRP roof can go over the old one only where the deck is checked and found dry and sound, and an overlay costs €1,800 to €5,000. Over a wet or rotten deck it traps the problem.
When an overlay works, when it doesn't, and how the deck is checked.
Free, no obligation. One local company prices it, not five.
An overlay can work if
- The deck is dry: no soft spots underfoot, no stains growing on the ceiling below.
- The deck is flat and firm enough to take a new board or the laminate.
- The roof's fall is right, so water still runs to the outlet.
- The extra height doesn't foul door thresholds, window sills or flashings.
A roofer can confirm the deck is dry with a moisture meter or a thermal camera, or by lifting a section. An overlay saves the stripping and the skip.
Strip it instead if
- The roof has leaked for a while: the deck boards are probably wet.
- It's springy or soft in places.
- There are two or more old layers already.
- You want insulation: that's a warm roof, built up from the deck.
Overlay or a new roof
| Job | Typical cost | What moves the price |
|---|---|---|
| GRP over the old roof | €1,800 to €5,000 | Only over a dry, sound deck |
| A GRP flat roof, garage or extension | €2,800 to €6,500 | Size, a new deck, trims on every edge, the outlet |
| New OSB3 deck where the old one has rotted | €30 to €50 a m² extra | How much of it is soft |
GRP jobs we cover
New GRP roofsStrip the old roof and lay GRP. €75 to €140 a m².More on new grp roofs →
Garage roofsThe commonest roof to go over to GRP. €1,800 to €5,200.More on garage roofs →
Extension roofsWith insulation over a heated room. €3,800 to €6,500 for 30 to 40 m².More on extension roofs →
Dormers and balconiesSmall roofs with lots of edges, and roofs you stand on.More on dormers and balconies →
GRP roof repairCracks, trims, outlets. €250 to €900.More on grp roof repair →Fibreglass roofing in every county
- Carlow1.4% flat main roofs
- Cavan0.8% flat main roofs
- Clare1.2% flat main roofs
- Cork2.5% flat main roofs
- Donegal1.0% flat main roofs
- Dublin3.0% flat main roofs
- Galway1.2% flat main roofs
- Kerry1.8% flat main roofs
- Kildare1.0% flat main roofs
- Kilkenny1.4% flat main roofs
- Laois1.2% flat main roofs
- Leitrim1.2% flat main roofs
- Limerick1.6% flat main roofs
- Longford0.9% flat main roofs
- Louth2.3% flat main roofs
- Mayo2.3% flat main roofs
- Meath1.3% flat main roofs
- Monaghan0.9% flat main roofs
- Offaly1.3% flat main roofs
- Roscommon1.2% flat main roofs
- Sligo1.4% flat main roofs
- Tipperary1.6% flat main roofs
- Waterford2.2% flat main roofs
- Westmeath1.5% flat main roofs
- Wexford2.7% flat main roofs
- Wicklow2.7% flat main roofs
Free quote
Get a price in 4 taps
Tap what you need and leave your number. It goes to one flat roofing company that covers your county, and they ring you back to arrange a look and a written price.
Questions people ask
Is it cheaper to put GRP over felt?
It can be: an overlay is €1,800 to €5,000 against €2,800 to €6,500 for a new GRP roof. It only makes sense over a sound deck.
Can GRP go straight onto felt?
Usually a new board goes over the old roof first, so the GRP is laid on a clean, dry deck. Ask the roofer what their system allows.
How do I know if the deck is wet?
Soft spots, a ceiling stain, or a roof that's leaked for months. The roofer can lift a section, or use a moisture meter or thermal camera.
Get a free price for a GRP roof
One local flat roofing company, a look at the roof, a written price. Free, no obligation.