If your home has a cavity wall with an empty gap inside it, cavity wall insulation is one of the best-value upgrades you can make: it is quick, relatively cheap, grant-supported at around 80 percent of the cost, and it targets the large share of heat that escapes through the walls, second only to the attic. Here is the grant by home type, how to tell if your home qualifies, and how it compares to the alternatives.
What is cavity wall insulation?
Many Irish homes are built with a cavity wall: an outer and an inner leaf of blockwork with a gap between them. Cavity wall insulation fills that gap with an insulating material, pumped in through small, neatly-made holes in the outer wall. Because it uses the space that is already there, it is fast and relatively inexpensive.
The SEAI cavity wall insulation grant (2026)
The grant is a fixed amount set by your home type:
| Home type | Cavity wall grant |
|---|---|
| Apartment | €700 |
| Mid-terrace | €800 |
| Semi-detached / end-terrace | €1,200 |
| Detached | €1,800 |
Homeowners on qualifying welfare payments can access up to €2,300. Because cavity filling is inexpensive, the grant covers around 80 percent of the average cost, which is why, where a suitable cavity exists, it is one of the highest-return upgrades available. See the full grant guide for every measure.
When is a cavity suitable, and when is it not?
Cavity filling is superb value, but only when the wall is right for it. A survey checks that the cavity is:
- Unfilled and clean, not already insulated or blocked with debris.
- Wide enough to take the insulation.
- Dry, with no penetrating damp or driving-rain exposure that isn’t properly protected.
If any of those fail, external or internal insulation is the better route. This is why cavity insulation should never be a rushed job: getting the survey right is what keeps the wall dry.
Cavity vs external vs internal insulation
| CavityBest value if you have a cavity | ExternalFor solid walls / full wrap | InternalFor one room / protected facade | |
|---|---|---|---|
| Needs | A clean, unfilled cavity | Any wall type | Any wall type |
| Cost | Lowest of the three | Highest | Middle |
| Disruption | Minimal, pumped in | None indoors | Rooms out of use |
| Grant (detached) | €1,800 | €8,000 | €4,500 |
| Refreshes exterior | No | Yes | No |
What does it cost, and what will you pay?
Because it is pumped into an existing cavity rather than built onto the wall, cavity insulation is one of the cheaper, faster measures, and with the grant covering around 80 percent, your net spend is small. The figure depends mainly on your home type and wall area. Use the estimator for an indicative figure, then we confirm the exact numbers at a free assessment.
Book a free assessment for your exact figure.
How the job works
The bottom line
For a home with a clean, unfilled cavity, cavity wall insulation is hard to beat on value: cheap, fast, grant-supported at around 80 percent, and a big comfort gain that lifts your BER. The only way to be sure it suits your walls is a quick survey.
If you are in Cork or across Munster, book a free home energy assessment and read our complete guide to SEAI grants to plan the full picture.
