Spray foam insulation
Spray foam is sprayed onto the underside of the roof at the rafters. It costs €50 to €100 per m², about €2,800 to €4,200 for a three-bed semi. Fitted badly, with no air gap under the felt, it can trap moisture against the rafters, it hides their condition, and it is hard to remove, so surveyors and some lenders ask about it.
What spray foam insulation is, why surveyors and lenders ask about it, and what to do if the house you own or want to buy has it.
Free and no obligation. Your plan goes to one contractor, not a list.
- €50–€100per m² at roof level
- €2,800–€4,200a three-bed semi's rafters
- €400–€800extra for vent cards
- 50 mmair gap it needs
The problem with it
- Moisture. Without a ventilated gap under old bitumen felt, moisture from the house can condense on the cold side and rot rafters and battens.
- Inspection. A surveyor can't see the timbers or the underside of the slates through foam, so a valuation may come with conditions.
- Removal. It is designed to stick, and taking it off is slow, careful work: often more than putting it on.
- Grants. SEAI's attic grant is for the attic floor, not foam on the rafters.
Open-cell and closed-cell foam
Open-cell foam is soft and lets water vapour through. Over a breathable membrane, with the air gap kept, the roof can still dry out. Closed-cell foam is rigid and blocks vapour. Sprayed straight onto old bitumen felt, it can hold moisture against the timbers where nobody can see it.
A surveyor wants to know which one it is, how thick, and whether the gap under the felt was kept. Ask the installer, or the seller, for the product and the date it went in.
Plan your roof insulation
A few quick taps, and your plan fills in as you answer: the right method for your roof, what it costs, the grant and the standard to ask for. Contact details come last, and only if you want a contractor to price it.
Insulation for a room in the roof, 30 m²: €3,000 to €5,400.
How the estimate is worked out
Attic floor insulation uses what SEAI-registered contractors were paid for each kind of home in 2026 and what an Irish installer charges, with the SEAI grant taken off. A room in the roof and a flat roof are priced per m² of the area you enter: rafter boards with a plasterboard finish, or a warm roof with a new membrane. VAT is included. Use it to plan with. It isn't a quote: a contractor prices your roof after a survey.
Thinking of having it sprayed?
For a cold attic, wool on the attic floor costs less, gets the SEAI grant and can be checked any time: attic insulation. For a room in the roof, rigid boards between and under the rafters, with the 50 mm air gap, do the same job and can be inspected later: rafter insulation.
If your house has it
Get it surveyed: the type of foam, whether there is a gap under the felt, and the state of the timbers where they can be seen. Open-cell foam over a breathable membrane with a ventilated gap is in better shape than closed-cell foam glued straight to old felt. Where it has to come off, removal is priced on the survey; then the roof is insulated properly, usually at the attic floor with a grant. Condensation and ventilation.
Where the insulation goes
Each roof in our drawings, with its own page: the method, the cost, the grant and what to watch for.
Attic insulationThe usual job: wool over the joists, a cold attic above, an SEAI grant towards it.Rafter insulationBoards between and under the rafters, so the whole attic stays warm.
Room in the roofSloping ceilings, knee walls and a small top ceiling, wrapped all round.
Insulating from aboveBoards over the rafters when the slates come off anyway.
Flat roof insulationA warm roof on the deck, or a cold roof with a vented gap.
Garage and extension roofsFlat or pitched, heated or not: what each needs.Questions before you insulate
Is spray foam bad for a roof?
Not always, but fitted with no ventilated gap it can trap moisture and hide rot. It is hard to inspect and hard to remove.
Will spray foam stop me getting a mortgage?
Irish lenders have said it isn't a reason for refusal in itself, but surveyors note it and a valuation may come with conditions.
How much does it cost to remove spray foam?
It is priced on a survey: the foam type, the area and the access decide it. It often costs more than fitting it.
Is there a grant for spray foam?
No. SEAI's attic grant is for insulating the attic floor.
Every guide and county page
Methods
Costs, grants and rules
Keep the heat under your roof
Pick the roof, what's there now and the home to see the method and the cost. When you want a firm price, your plan goes to a single vetted insulation contractor for your area.