Insulating a roof from above
When a pitched roof is stripped for new slates or tiles, rigid insulation boards can be laid over the rafters, under new battens and the new covering. The rooms below keep all their headroom, the rafters can be left on show, and there are no cold stripes. It raises the roof by the thickness of the boards.
When the slates or tiles come off anyway, the insulation can go on top of the rafters instead of under them.
Free and no obligation. Your plan goes to one contractor, not a list.
- 0 mmlost from the rooms below
- 1scaffold for the roof and the insulation
- 0.16W/m²K to aim for
- 2jobs done at once
How it works
- Strip the old covering down to the rafters, as for any re-roof.
- Lay a vapour control layer over the rafters, then rigid boards across them.
- Fix counter-battens and battens through the boards with long screws, and a breathable membrane over the boards.
- Re-slate or re-tile, with deeper fascias and verges to finish the extra thickness.
What to check first
The roof gets thicker, so the fascia, the gutters and the joint with the neighbour's roof on a semi or terrace need detailing. On a protected structure, or where the change in height is visible, ask the council. Price the insulation with the re-roof so you aren't paying for a second scaffold later. Not re-roofing? Insulate from inside instead: rafter insulation.
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.
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.
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
Can you insulate a roof from the outside?
Yes, when the roof is being stripped: boards go over the rafters under new battens and slates.
Does over-rafter insulation raise the roof?
Yes, by the thickness of the boards and battens, so the eaves and verges are re-detailed.
Is it better than insulating between the rafters?
Thermally, yes: no timber breaks the layer and no headroom is lost. It only makes sense when the roof is coming off anyway.
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.