Rafter insulation
Rafter insulation puts rigid boards between the rafters, keeping a 50 mm air gap under the felt, with insulated plasterboard across the underside. The whole roof space stays warm. Finished, it costs €100 to €180 per m² of roof slope, and it is grant-aided only within a One Stop Shop upgrade.
Insulating along the slope of a pitched roof, so the attic is inside the warm part of the house.
Free and no obligation. Your plan goes to one contractor, not a list.
- €100–€180per m², finished
- 50 mmair gap kept under the felt
- 0.16W/m²K to aim for
- 6%of BER roofs are insulated this way
How it's built
- Check the felt. Older bitumen felt doesn't breathe, so the air gap under it must be kept open from eaves to ridge. Breathable membranes give more choice.
- Boards between the rafters. Cut tight, leaving the gap above. Rafters are often only 100 to 150 mm deep, which limits how much fits between them.
- A second layer under the rafters. Insulated plasterboard covers the timber, which would otherwise be a cold stripe every 400 mm.
- Seal it. Taped joints or a vapour control layer on the warm side stop moist air getting into the roof.
When to choose it
- The space under the roof is used, or will be.
- There are tanks, a cylinder, ducts or a boiler in the attic you want kept warm.
- The ceiling below is full of downlighters, or hard to get at.
It costs more than the attic floor because more area is insulated and it is finished in plasterboard. If the attic is only for boxes, the attic floor is cheaper and grant-aided.
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.
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.
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
What is the cost of rafter insulation in Ireland?
€100 to €180 per m² of roof slope for boards with an insulated plasterboard finish.
Is there a grant for rafter insulation?
Only through a One Stop Shop whole-home upgrade. SEAI's individual roof grant is for the attic floor.
Do I need an air gap behind rafter insulation?
Yes, 50 mm under the felt, from eaves to ridge, unless the roof has a breathable membrane designed to touch the insulation.
Warm roof or cold roof?
Insulate where the warmth should stop. If the attic is only for storage, insulate the attic floor and keep the attic cold and ventilated. If people use the space under the roof, insulate at the rafters, all round the room. A flat roof is usually insulated on top of the deck as a warm roof, ideally when it is re-covered.
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.