After the attic, walls are usually the next biggest route for heat to escape. There are three ways to insulate them, and they differ several-fold in price. The right one is decided mostly by how your walls are built, and then by your budget and how much disruption you can live with.
Step 1: work out what walls you have
You can’t choose an option until you know the wall type. These clues help, but confirm with a survey:
| Clue | Suggests a cavity wall | Suggests a solid wall |
|---|---|---|
| Age of house | Mid-20th century onwards is often cavity | Older houses are more often solid |
| Wall thickness at a window or door opening | Thicker overall, with a gap between two leaves | One continuous layer of masonry |
| Brick pattern (exposed brick) | Only the long side of bricks showing | A pattern of long sides and short ends |
| Construction records / previous BER | Records a cavity or filled cavity | Records solid or hollow block |
Many Irish homes are rendered, so the brick pattern is often hidden — another reason a contractor’s survey or a BER assessment is the reliable answer.
Step 2: compare the grants for your house type
| Type | Apartment | Mid-terrace | Semi/End-terrace | Detached |
|---|---|---|---|---|
| Cavity wall | €700 | €850 | €1,300 | €1,800 |
| Internal (dry lining) | €1,500 | €2,000 | €3,500 | €4,500 |
| External wall | €3,000 | €3,500 | €6,000 | €8,000 |
The three options compared
Cavity wall insulation
Insulating material is blown into the gap between the inner and outer leaves of the wall through small holes that are then filled.
- Cost and disruption: the lowest of the three; often done in a day with little mess inside.
- Suitability: the cavity must be suitable — not already filled, and not on a wall exposed to severe driving rain without the contractor confirming the product is appropriate.
- What to ask: how they checked the cavity, which product and how it is certified, and how they will treat vents and openings.
Internal wall insulation (dry lining)
Insulated boards are fixed to the inside face of external walls, then finished and decorated.
- Cost and disruption: mid-range; done room by room, but furniture, skirting, sockets and radiators on those walls come off and go back.
- Space: each treated room loses a little floor area.
- Detailing matters: cold spots can form where floors, ceilings and window reveals meet the wall, so ask how those junctions and condensation risk are handled.
External wall insulation
An insulation layer is fixed to the outside of the house and finished with a new render or cladding.
- Cost and disruption: the highest cost, but most of the work happens outside; scaffolding is needed.
- Performance: treats the whole wall continuously and keeps the masonry warm; no lost room space.
- Appearance: the house looks different afterwards; sills, downpipes and eaves may need extending. If the house is a protected structure or in an architectural conservation area, check with your local authority first.
Which suits you?
| Your priority | Usually the better fit |
|---|---|
| You have a suitable cavity | Cavity wall insulation |
| Lowest cost on solid walls | Internal dry lining |
| Keep the outside unchanged | Internal dry lining |
| Don’t lose room space | External insulation |
| Whole house at once, best performance | External insulation |
| One room at a time | Internal dry lining |
A worked comparison
Purely illustrative figures for a solid-wall, semi-detached house, using the grant table above:
- Internal dry lining: quote €9,000 − grant €3,500 = €5,500 net, plus redecorating the rooms affected.
- External insulation: quote €16,000 − grant €6,000 = €10,000 net, with the exterior refreshed and no lost floor space.
The difference of €4,500 buys better continuity of insulation and no internal disruption. Whether that’s worth it depends on how long you’ll stay, the condition of the existing render and whether you want to keep the house’s appearance. Get written quotes for both before deciding — and compare like with like using our quote checklist.
Questions to ask any wall insulation contractor
- Are you SEAI-registered for this specific measure?
- What did your survey find about the wall construction and any damp?
- Exactly which areas are included — every external wall, gables, reveals, bay windows?
- How will you treat junctions, window reveals and ventilation?
- What is excluded: decorating, moving radiators or sockets, extending sills and downpipes?
- What warranty or guarantee applies, and who issues it?
