Insulation
Warm Flat Roofs and Insulation
A warm flat roof, with insulation boards on the deck under the new membrane, costs €130 to €190 a m², or €6,000 to €9,500+ for a 35 to 50 m² heated extension. Doing it when the roof is replaced costs least.
Warm, cold and inverted roofs, what the upgrade costs, and the SEAI rule.
Free, no obligation. One local company prices it, not five.
Warm, cold and inverted
Warm roof: the insulation sits on top of the deck, under the waterproof membrane, with a vapour control layer below it. The deck and joists stay warm and dry. It's what most roofers now fit on a heated room.
Cold roof: the insulation is between the joists, under the deck, with a ventilated gap above it. Common on older extensions. If the ventilation or the vapour control isn't right, moisture from the room condenses under the deck: see condensation.
Inverted roof: the membrane is on the deck and the insulation goes on top of it, held down by ballast or paving. Used on terraces and commercial roofs.
What a warm roof costs
The difference between a plain re-cover and a warm roof is the insulation boards, the vapour control layer and the taller trims and upstands. The roof gets thicker, so check the height at the wall, under windows and at a door onto the roof.
| Job | Typical cost | What moves the price |
|---|---|---|
| Warm roof on a heated extension, 35 to 50 m² | €6,000 to €9,500+ | Insulation boards, vapour control, taller trims |
| Warm roof system, a m² | €130 to €190 | Boards, vapour control, membrane |
| EPDM, a plain re-cover, a m² | €70 to €140 a m² | No insulation |
| GRP, a plain re-cover, a m² | €75 to €140 a m² | No insulation |
SEAI and flat roofs
SEAI's roof insulation rules count flat roofs: extensions, flat roofs and room-in-roofs are among the roof areas that must be insulated for a roof insulation grant, where that's physically and economically feasible. Grants are applied for before work starts, through SEAI or a One Stop Shop. Check the current amounts for your house on seai.ie before you sign anything.
Flat roof jobs we cover
Flat roof replacementExtensions, garages and dormers. €3,000 to €6,500 on a kitchen extension.More on flat roof replacement →
Flat roof repairLeaks, blisters, split seams, outlets. €250 to €900.More on flat roof repair →
EPDM rubber roofsOne sheet, no flame. €70 to €140 a m² laid.More on epdm rubber roofs →
GRP fibreglass roofsHard and walkable. €75 to €140 a m² laid.More on grp fibreglass roofs →
Torch-on felt roofsThe lowest cost. €55 to €90 a m² laid.More on torch-on felt roofs →Flat roofs 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
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Questions people ask
Is a warm roof worth it?
On a roof over a heated room, usually: the deck stays dry, condensation stops, and the room is warmer. On a garage nobody heats, a plain re-cover is fine.
Does a warm roof raise the roof level?
Yes, by the thickness of the insulation. The trims, the upstands at the wall and any rooflight kerbs have to suit the new height.
Can I get a grant for flat roof insulation?
SEAI's roof insulation rules include flat roofs. Check the current grant and apply before any work starts.
What is a cold flat roof?
One insulated between the joists, under the deck, with a ventilated gap above. Many older extensions are built that way.
Get a free price for your flat roof
One local flat roofing company, a look at the roof, a written price. Free, no obligation.