Garage and extension roofs
A heated extension or converted garage needs its roof insulated like the house: a warm flat roof at €130 to €190 per m² with a new membrane, or rafter boards at €100 to €180 per m² finished under a pitched roof. An unheated garage only needs it if you want to cut condensation or use it as a workshop.
Flat or pitched, heated or not: what each needs before you spend money on it.
Free and no obligation. Your plan goes to one contractor, not a list.
- €130–€190per m², warm flat roof
- €100–€180per m², pitched, finished
- 0.20W/m²K, flat roof
- 0needed in a cold store
Heated rooms
A kitchen extension, a garage converted into a bedroom or an office, or a garden room used all year: the roof is insulated to the same level as new work on the house, and the walls and floor are too. Converting a garage: see garageconversion.ie for the planning and building rules.
Unheated garages and sheds
A cold garage doesn't need its roof insulated, but metal or fibre-cement sheets drip condensation onto cars and tools. An anti-condensation lining, or a breathable membrane and boards under the sheets, stops it. Old fibre-cement sheets may contain asbestos: have them checked before anyone drills or cuts them.
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.
A warm flat roof, 20 m²: €2,600 to €3,800.
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.
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.Questions before you insulate
Should I insulate my garage roof?
If the garage is heated or used as a room, yes. If it is a cold store, only to cut condensation.
How much does it cost to insulate an extension roof?
As a warm flat roof with a new membrane, €130 to €190 per m²: €3,300 to €4,800 for 25 m².
Can I insulate under a corrugated garage roof?
Yes, with an anti-condensation lining or boards under a breathable membrane. Check old sheets for asbestos first.
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.