What attic insulation is, and why it goes first
Attic insulation is a thick layer laid over the ceilings of the top rooms. Heat you paid for stays in the rooms instead of rising into a cold roof.
What the job is
Two rolls of mineral wool, laid at right angles to each other over the attic floor, to a depth of about 300 mm. That's the whole job in most houses. The contractor lays it over the joists rather than between them, boards a walkway to the water tank and the hatch, lags the tank and the pipes, and makes sure air can still move through the roof space.
It takes half a day. Nobody moves out, nothing gets knocked, and the only thing you lose is headroom in the attic for storage.
If the attic is a bedroom or a playroom, the layer goes against the slope of the roof instead, in rigid boards. That's a different job with a different grant, and it costs more.
Compared with a cold roof
| Before | After | |
|---|---|---|
| What's up there | patchy wool between the joists, often 100 mm | about 300 mm, laid across the joists |
| Where the heat goes | up through the ceiling and out the roof | stays in the rooms below |
| The attic itself | mild, because your heat is warming it | properly cold, and ventilated for it |
| Storage | anything, anywhere | a boarded walkway; boxes need raised boards |
| Time and mess | — | half a day, no rooms cleared |
SEAI's figure for a badly insulated roof and walls together is up to 30% of a home's heat. That's the reason this job goes first: it is the cheapest thing on the list and it takes the biggest single bite out of the loss.
Grant €1,100 to €2,000 by house type, €1,500 for a semi-detached or end of terrace; rafter-level work €1,500 to €3,000. SEAI median cost €2,000 (semi). Grant paid once per MPRN. Amounts verified 2026-09-07.
Where the saving comes from
Warm air rises, and a ceiling is thin. Insulation doesn't stop heat, it slows it down: the wool traps air in tiny pockets, and still air is a poor conductor, so the heat takes far longer to get through. Slow the loss and the boiler or the heat pump runs for fewer hours to hold the same room temperature. Nothing about the heating system changes — it just has less work to do.
This is also the job that makes every later job cheaper. A house that holds its heat needs a smaller heat pump, and it is the attic and the walls that usually get an older house through SEAI's heat-loss test.
Modelled roof heat loss for that group of homes: U 0.26 → 0.20 W/m²K after the works. SEAI's standard for a grant-aided attic job is 0.16 W/m²K, roughly 300 mm. detached|1970-1989|D|oil: cost p50 €36,393, grant €19,000, net p25–p75 €9,019–€23,200, saving €1,791/yr, payback 5.8–13.6 yrs, n=23,707, confidence 0.9
Is it right for a house like yours?
Your cert may say B2 — that's a B on the new scale.
A heat pump runs on electricity. Pick "Heat pump" if you have one.
A 1970s–80s detached house on oil, rated DEnergy rating D
- Grants you’d get
- €19,000
- It costs about
- €36,400
- You pay
- €9,000 – €16,300
- Saves you each year
- about €1,790
- Pays for itself in
- about 9 years
The commonest home on file — 23,707 like it. Change an answer above for yours.
Modelled, not observed payments. Middle case €16,329; a quarter of these homes are over €23,200. Repaid in 9.1–13.6 years. Confidence 0.9. One job in this list has no SEAI median price, so its cost is an estimate.
Show what’s included
This is the job list that suits most homes like yours (2 in 10). The money above is the middle of every route we priced, so it will not add up to this list exactly.
Attic insulation — a thicker blanket in the roof space. Half a day, nobody moves out, you lose some storage height.
Roof U-value → 0.16 W/m²K (≈300 mm). Cost €2,000 · grant €1,500 · you pay €500.
Costs about €2,500 · grant €2,000 · you pay €520
Wall insulation — the walls get a warm coat: pumped into the cavity (a morning), fitted inside (rooms shrink about 10 cm, redecorate, one to two weeks) or wrapped outside (scaffolding, new render, two to four weeks). We pick what your walls allow.
Cavity → 0.55, €1,550 · grant €1,300 · pay €250. Internal → 0.27, €10,420 · €3,500 · €6,920. External → 0.21, €23,247 · €6,000 · €17,247. Pre-1970 solid walls can't take cavity fill.
Costs about €9,000 · grant €4,500 · you pay €4,500
New windows and doors — double or triple glazed, fitted a room at a time over two to three days. You need not do every window, but the grant is paid once.
Whole-window U → 1.4 W/m²K. Estimate: €490/m² of window (no SEAI median), about €9,085 on a semi-detached house. Grant €3,000 + €800/door (max 2).
Estimated at €13,700 · grant €4,000 · you pay €9,700
Is the house warm enough to hold the heat? — SEAI's test before they'll fund a heat pump. The insulation steps are usually what gets you through.
Heat Loss Indicator ≤ 2.3 W/K·m² after fabric works. 1% of homes like yours already pass. Assessment about €276, grant €350 through a One-Stop-Shop.
Costs about €280 · grant €350 · the grant covers it
Heat pump — replaces the boiler, runs on electricity, pulls heat from the outside air. An outdoor unit the size of a large suitcase, bigger radiators in some rooms, three to five days. Runs cooler for longer — the house feels even, not blasted.
Air-to-water, SPF 3.5 heating / 2.5 hot water. Cost €16,832 · grant €6,500 + €4,000 (replacing oil/gas/coal) + €2,000 pipework + €700 controls = up to €13,200 · you pay from €3,632. 9.8c per kWh of heat vs gas 14.4c / oil 18.0c.
Costs about €16,500 · grant €6,500 · you pay €10,000
The paperwork — assessment first, grant approval, then the work, then a new energy cert, then the grant is paid. A One-Stop-Shop does all of it and takes the grant off the bill.
Order is mandatory — work started before approval is not eligible. Energy cert €276, assessment grant €350 through a One-Stop-Shop. Typically 3–6 months end to end (estimate).
Costs about €280 · grant €350 · the grant covers it
Common questions
- How much insulation is enough?
- SEAI put the ideal at 300 mm at ceiling level. Older houses often have 100 mm that has settled, gone patchy, or was never laid over the joists at the eaves. Topping up to 300 mm counts as a job worth doing, and it is what the grant is for.
- Can I still use the attic for storage?
- Yes, but not the way you used it before. The insulation is deeper than the joists, so anything resting on the joists is now squashing it. A proper job includes a boarded walkway to the tank and the hatch. If you store a lot up there, ask the contractor to raise the boards above the insulation.
- Will the attic get damp?
- It can, if the job is done badly. A cold attic needs air moving through it, because the moisture that used to drift up and out now has to leave some other way. SEAI are explicit that ventilation goes in as part of the work. The tank and its pipes get lagged at the same time, because the attic is now colder than it used to be.
Where to next
Where this comes from
Last checked 2026-09-08.