Cavity wall insulation grant: €700 – €1,800
Homes built from about 1970 on usually have the gap this needs; a detached house gets €1,800 because it has the most outside wall.
What would it cost on your home?
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
Do you qualify?
- Your home was built and lived in before 2011.
- The outside walls have a gap between two skins of block.
- The gap is dry and clear — the installer drills and checks first.
Roughly 1 in 10 1970s–80s detached homes already pass the first check.
What it costs for homes like yours
Worked out from the energy ratings of 23,707 homes like these in SEAI’s records. “You pay’ is what is left after the grants, for the middle half of them.
| Home | Grant | You pay | Saves a year | Pays back in |
|---|---|---|---|---|
| A 1970s–80s detached house on oil, rated DEnergy rating D | €19,000 | €9,000 – €16,300 | €1,790 | 9 years |
| A pre-1970 detached house on oil, rated F/GEnergy rating F/G | €23,000 | €13,300 – €18,100 | €4,150 | 5 years |
| A 1990s detached house on oil, rated DEnergy rating D | €19,000 | €8,500 – €12,300 | €1,280 | 10 years |
| A pre-1970 terrace house on gas, rated DEnergy rating D | €15,900 | €6,800 – €7,400 | €1,110 | 9 years |
detached|1970-1989|D|oil: net p50 €16,329, p75 €23,200, repaid 9.1–13.6 yrs, confidence 0.9 · detached|pre1970|FG|oil: net p50 €18,106, p75 €25,076, repaid 4.5–6.4 yrs, confidence 0.9 · detached|1990-2005|D|oil: net p50 €12,294, p75 €17,906, repaid 10.1–14 yrs, confidence 0.9 · terrace|pre1970|D|gas: net p50 €7,403, p75 €11,932, repaid 8.6–11.5 yrs, confidence 0.9.
More home types
| A 1990s detached house on oil, rated C | €12,500 | €4,000 – €4,500 | €820 | 7 years |
|---|---|---|---|---|
| A 1990s semi-detached on gas, rated C | €12,500 | €4,300 | €540 | 11 years |
| A 1990s semi-detached on oil, rated C | €12,500 | €4,300 | €470 | 11 years |
| A 1970s–80s detached house on oil, rated C | €10,300 | €5,000 – €8,900 | €760 | 15 years |
Why oil homes pay back fastest
The dearer your heat is now, the more you save by changing it. A unit of heat from a heat pump costs about a third of what the same heat costs on electric heating, and well under what it costs on oil or bottled gas.
What’s entailed
Cavity wall insulation — beads pumped into the gap between the two skins of your outside walls. A morning's work, nobody moves out, no redecorating.
Wall U-value → 0.55 W/m²K. Cost €1,550 · grant €1,300 · you pay €250. Pre-1970 solid walls can't take cavity fill.
Costs about €1,600 · grant €1,300 · you pay €250
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 €2,000 · grant €1,500 · you pay €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 €9,100 · grant €3,000 · you pay €6,100
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 €16,800 · grant €6,500 · you pay €10,300
The grant in detail, by house type
| Apartment | €700 |
|---|---|
| Terrace | €850 |
| Semi-detached or end of terrace | €1,300 |
| Detached | €1,800 |
- Older solid walls cannot take this. Those homes get insulation fitted inside or wrapped outside instead.
- It is the cheapest wall job by a distance, so it is usually done first.
- You can take it on its own, or as part of a bigger job through a One-Stop-Shop.
Amounts verified 2026-09-08.
How we worked this out
We group every home in SEAI’s energy rating records by kind, age, rating and heating, then work out the cheapest set of jobs that would bring each one up to a B. Prices for those jobs are the middle price SEAI recorded for that work last year; grants come from SEAI’s published amounts; fuel prices come from SEAI’s comparison table.
So these are worked-out figures for homes like yours, not a record of what anyone was charged. Your own quote will land somewhere in the range, and the wider the range, the less certain we are.
2025 medians (n=47,067 upgrades; OSS n=1,406). 2026-07-01. BER file 2026-09-08, 1,077,114 rows. DEAP standard occupancy.
Common questions
- How do I know if my walls have a cavity?
- Homes built from about 1970 on nearly always do. The installer drills a small hole and looks with a camera before quoting.
- How much does it cost after the grant?
- The middle price for the work in 2025 was €1,550 for a semi-detached house. With the €1,300 grant you pay about €250.
- Will it cause damp?
- Not when the walls are dry and the work is done by a registered installer. Walls that already get wet have to be fixed first.
Related
Homes at each rating
- Detached 1971–1980: D to B
- Detached 1991–2000: D to B
- Detached 1981–1990: D to B
- Detached before 1919: G to B
- Semi-detached 1971–1980: D to B
- Detached 1919–1945: G to B
Applying, and who gets what
- One-Stop-Shop
- One job at a time
- Free upgrades scheme
- How to apply
- How long the wait is
- What you need first
- Checking your application
- If you are retired
Who does this work
Registered installers by county