Attic insulation
Attic floor insulation means laying mineral wool between the ceiling joists and a second layer across them, to about 300 mm, so the rooms below keep their heat and the attic stays cold and ventilated. It costs €1,800 to €2,101 for a semi-detached house before an SEAI grant of €1,500.
Insulating the attic floor, the way most Irish homes are done: what goes in, what it costs after the grant, and what the contractor must keep clear.
Free and no obligation. Your plan goes to one contractor, not a list.
- 300 mmof mineral wool, in two layers
- 0.16W/m²K, the level to reach
- €1,500SEAI grant, semi-D
- 1 dayfor most attics
What attic insulation costs, with the grant
| Home | Attic insulation | SEAI grant | Left to pay |
|---|---|---|---|
| Detached house | €2,400 to €2,700 | €2,000 | €400 to €700 |
| Semi-detached or end-of-terrace house | €1,800 to €2,101 | €1,500 | €300 to €601 |
| Mid-terrace house | €1,600 to €2,200 | €1,400 | €200 to €800 |
| Top-floor apartment | €1,200 to €1,515 | €1,100 | €100 to €415 |
VAT included. A semi-detached house with nothing much in the attic now usually lands near the middle of its range. Boarded floors, a water tank to lift and downlighters in the ceiling below push it up. By home, by attic size and at the higher grant rate: attic insulation cost. Who qualifies and how to claim: the attic insulation grant.
What a good job includes
- Two layers, crossed. One between the joists, the next across them, so the timber doesn't leave cold stripes.
- Eaves kept open. Trays or vents at the eaves stop the wool blocking the air that keeps the roof timbers dry.
- Tank and pipes lagged. The attic gets colder once the floor is insulated, so the water tank and pipes need covering, but not under the tank.
- The hatch done. An insulated, draught-stripped hatch, or the heat goes straight up through it.
- Walkways raised. Boarding laid on the joists crushes the wool. Raised legs keep the full depth under a storage floor.
- Wiring and downlighters checked. Cables are lifted on top, and light fittings get covers that let them stay cool.
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.
Attic floor insulation, semi-d or end of terrace: €1,800 to €2,101 before the €1,500 SEAI grant, so about €300 to €601 to pay.
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.
How the day goes
- Before: the grant is approved, and the attic is cleared, or the contractor quotes to lift what's stored there.
- Morning: eaves trays go in, the old wool is checked and levelled, and the first layer is laid between the joists.
- Afternoon: the second layer goes across, the tank and pipes are lagged and the hatch is insulated and draught-stripped.
- After: the contractor signs the declaration of works so you can claim the grant.
When the attic floor isn't the answer
If the space under the roof is used, as a bedroom, an office or a playroom, insulating the floor of it leaves that room cold. Insulate at the rafters instead, all round the room. Room in the roof insulation.
If the attic holds a heat pump cylinder or ducts you want kept above freezing, insulating at the rafters keeps them inside the warm envelope too.
Where the insulation goes
Each roof in our drawings, with its own page: the method, the cost, the grant and what to watch for.
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
How much does attic insulation cost?
€1,800 to €2,101 for a semi-D and €2,400 to €2,700 for a detached house, VAT included, before the SEAI grant. Attic insulation cost.
How thick should attic insulation be?
For new work, the Building Regulations ask for 0.16 W/m²K in a pitched roof, whether it is insulated at the ceiling or along the slope, and 0.20 W/m²K in a flat roof. About 300 mm of mineral wool on an attic floor gets there.
Can new insulation go over the old?
Yes, if the old layer is dry and even. Damp, compressed or patchy wool should come out first.
Does attic insulation need ventilation?
Yes. A cold attic needs air at the eaves or through vent tiles, so the roof timbers and felt stay dry.
How much is the grant for attic insulation?
SEAI's individual grant for roof insulation is for the attic floor: €2,000 for a detached house, €1,500 for a semi-D or end of terrace, €1,400 for a mid-terrace and €1,100 for a top-floor apartment, with higher amounts for first-time buyers of an older home and some people on welfare payments. Rafter and room-in-roof insulation are grant-aided only as part of a One Stop Shop whole-home upgrade.
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.