Compare · checked 28 October 2026
External, internal and cavity insulation compared
Three ways to insulate walls, three SEAI grants. Here's what each costs, what it involves and which suits your house.
Figures checked against seai.ie and saveonheat.ie on 28 October 2026.
Cavity fill is the lowest-cost wall insulation but only works on cavity walls. Internal insulation (dry lining) works on any wall but takes room space and disrupts every room it touches. External insulation (the wrap) also works on any wall, keeps your rooms the same size, and is the biggest and dearest job.
SEAI grants all three. For a semi-D: €1,300 cavity, €3,500 internal, €6,000 external (seai.ie wall insulation page, checked 28 October 2026).
Grants and typical costs
| Cavity fill | Internal (dry lining) | External (the wrap) | |
|---|---|---|---|
| Grant, detached | €1,800 | €4,500 | €8,000 |
| Grant, semi-D or end of terrace | €1,300 | €3,500 | €6,000 |
| Grant, mid-terrace | €850 | €2,000 | €3,500 |
| Grant, apartment | €700 | €1,500 | €3,000 |
| SEAI median cost, semi-D | €1,500 | €10,532 | €23,333 |
| SEAI median cost, detached | €2,250 | €9,000 | €24,000 |
| SEAI median cost, mid-terrace | €1,100 | €6,530 | €13,500 |
Grants: seai.ie wall insulation page, checked 28 October 2026. Median installed costs: SEAI median installed costs, H1 2025, incl. VAT, as published by saveonheat.ie (updated 13 October 2026).
What each costs after the grant, semi-D
| Measure | SEAI median cost | Grant | After grant |
|---|---|---|---|
| Cavity fill | €1,500 | €1,300 | €200 |
| Internal (dry lining) | €10,532 | €3,500 | €7,032 |
| External (the wrap) | €23,333 | €6,000 | €17,333 |
For a semi-D, the grant covers most of a cavity fill, about a third of dry lining and about a quarter of the wrap. The wrap also replaces the outside finish of the house, which dry lining doesn't. That's part of what the extra money buys. The figures are SEAI medians for H1 2025, incl. VAT, less today's grants.
How they compare
| Cavity fill | Internal (dry lining) | External (the wrap) | |
|---|---|---|---|
| Wall types | Cavity walls only | Any wall | Any wall |
| Room size | No change | Rooms lose some space on outside walls | No change |
| Disruption inside | Little | High: rooms emptied, sockets, skirting and radiators moved | Little: work is outside |
| Outside look | No change, holes filled | No change | New render or finish |
| Planning permission | Not required | Not required | Usually exempt under Class 63 (150 mm rule) |
| Typical time | Usually a day | Room by room | Weeks, with scaffold |
Planning: SEAI says planning permission is not required for internal or cavity insulation. External: S.I. No. 341 of 2026.
Which suits your house
- Empty cavity walls: start with cavity fill. It's the smallest job and the grant covers most of it. Our sister site cavitywallinsulation.ie has the cavity grant check.
- Solid walls, or cavity already filled: internal or external. External suits a house that needs new render anyway, or where you don't want to lose room space.
- Timber frame: don't fill the cavity. Talk to a contractor about the options.
- Traditional pre-1940 stone or brick: not funded under Better Energy Homes. See the Traditional Homes Pilot.
Doing more than one
You can't stack grants on the same walls in one go, but SEAI's second wall measure lets a home that had cavity or internal insulation go further later (see second wall measure). After cavity: internal or external. After internal: external only. After external: none. See second wall grant.
The heat pump angle
SEAI designed the second wall measure to help homes become heat pump ready. A heat pump suits a house that holds its heat. If a heat pump is in your plans, insulating the walls first is the usual order.
Questions to ask before you choose
- What are my walls: cavity, solid or timber frame?
- Is the cavity empty, part-filled or full?
- Does the outside need new render anyway?
- How much room space would dry lining take?
- Would the wrap fit within 150 mm and stay off the footpath?
- What's the price after the grant for each?
Questions people ask
Should I choose internal or external insulation?
Neither is right for every house. External keeps room sizes and avoids indoor disruption but costs more. Internal costs less but takes space and disrupts each room.
Is cavity wall insulation enough?
For many cavity-wall homes it's a good first step. A home that had a cavity grant can later apply for internal or external insulation as a second wall measure.
Which needs planning permission?
Internal and cavity insulation don't. External insulation to a house is usually exempt under Class 63, within the 150 mm and appearance rules.
Which grant is biggest?
External: up to €8,000 for a detached house, against €4,500 internal and €1,800 cavity.
Sources (1)
Prices and facts on this page were checked against these published pages. We are not connected to these businesses.
- saveonheat.ie: saveonheat.ie
See your grant, then get a price
Three taps show the SEAI grant for your home. Or call 087 162 1846 between 8am and 8pm and we pass you to one SEAI-registered external insulation contractor who covers your area.