Not every home can take external wall insulation, and not every wall has a cavity to fill. When your walls are solid, or the outside of your home has to stay exactly as it is, internal wall insulation, also called dry lining, is how you still get warm walls and a strong SEAI grant. Here is what it costs, when it is the right call, and the detailing that makes or breaks it.
What is internal wall insulation?
Internal wall insulation is fitted to the inside face of your external walls: an insulated board or a stud-and-insulation build-up, finished with plasterboard and skim ready to paint. Because it goes on the inside, it does not change the outside of your home at all, which is exactly why it exists as an option.
The SEAI internal wall insulation grant (2026)
Like other insulation measures, the grant is a fixed amount set by your home type:
| Home type | Internal wall grant |
|---|---|
| Apartment | €1,500 |
| Mid-terrace | €2,000 |
| Semi-detached / end-terrace | €3,500 |
| Detached | €4,500 |
That is a substantial contribution, larger than the cavity grant, reflecting the bigger job, though less than the external wall insulation grant, which tops out at €8,000. See the full grant guide for every measure.
When is internal wall insulation the right choice?
Internal insulation is the answer in four specific situations:
No cavity to fill
Solid stone or single-leaf walls with no cavity, where you don’t want, or can’t have, external insulation.
The outside must stay
A protected structure or architecturally-important frontage that has to remain exactly as it is.
Treat a room, not the house
A single north-facing or chronically cold room, upgraded on its own without a whole-house project.
Access or planning limits
Boundary right on the path, or planning constraints that rule out external render and scaffolding.
| Internal (dry lining)When outside must stay as-is | ExternalBest performance if allowed | CavityIf you have a fillable cavity | |
|---|---|---|---|
| Changes exterior | No | Yes (new render) | No |
| Room size | Slightly reduced | Unchanged | Unchanged |
| Cold bridges | Need careful detailing | Eliminated | Reduced |
| Disruption | Rooms cleared, room by room | None indoors | Minimal |
| Grant (detached) | €4,500 | €8,000 | €1,800 |
For most homes that can take external, external wall insulation performs better because it wraps the whole building and removes cold bridges. Internal comes into its own when external is off the table.
The detailing that matters
Internal insulation is the measure where quality of installation matters most. Done well, it is warm, dry and permanent. Done badly, trapped moisture can cause damp behind the boards. Proper work means:
- Careful vapour and airtightness control so warm, moist indoor air cannot reach the cold wall behind.
- Continuous insulation at reveals, floors and ceilings to limit cold bridges.
- Neat reinstatement of skirting, sockets, switches and radiators.
What does it cost?
Internal wall insulation costs more than cavity filling but less than a full external wrap, and the grant covers a meaningful share. The final figure depends on the wall area, the number of rooms, and how much reinstatement is involved. Use the estimator for an indicative fabric figure, then we confirm exact numbers at a free assessment.
Book a free assessment for your exact figure.
How the job works
The bottom line
Internal wall insulation is the right route when the outside of your home has to stay as it is, or your walls are solid with no cavity. It brings warm walls, a big BER improvement and a grant of €1,500–€4,500, as long as it is detailed and installed properly.
If you are in Cork or across Munster, book a free home energy assessment and read our complete guide to SEAI grants to compare every option for your home.
