Cavity wall insulation is the cheapest and least disruptive wall upgrade for most Irish homes — typically €1,000–€2,000 installed before grant, with the SEAI grant covering much of that. For eligible households it can be fully funded through the Warmer Homes Scheme.
How cavity fill works
Homes built from roughly the 1940s onwards usually have a cavity: two leaves of block or brick with an air gap between. If that gap was never insulated, the installer drills a grid of small holes in the outer leaf, pumps in insulation (commonly EPS beads or bonded mineral wool), and reseals the holes. Everything is done from outside in about a day, with no internal mess.
Walls account for around 25–35% of heat loss in an uninsulated house, so filling an empty cavity delivers a fast payback — often inside 3–5 years.
Installed cost
Before any grant, expect installed pricing in this range:
| Item | Typical installed cost |
|---|---|
| Cavity fill, lower end | €1,000 |
| Cavity fill, higher end | €2,000 |
Larger detached homes sit toward the higher end. As always, get three written quotes from SEAI-registered installers.
SEAI grants: standard and welfare rates
Cavity wall grants come in two tiers. The welfare/medical-card rate is a higher amount for households that hold a valid medical card or qualify on welfare grounds:
| Dwelling | Standard grant | Welfare / medical-card rate |
|---|---|---|
| Detached | €1,800 | €2,300 |
| Semi-detached / end-terrace | €1,300 | €1,700 |
| Mid-terrace | €850 | €1,100 |
| Apartment | €700 | €900 |
Because the installed cost is low and the grant is generous, the net cost after grant is often only €200–€700 — one of the best returns of any SEAI measure. The home must pre-date the relevant cut-off, the work must be done by a registered contractor, and a post-works BER is required. See the insulation grants guide for the detail.
The free route: Warmer Homes Scheme
If you receive qualifying social welfare payments, you may not need the partial grant at all. The SEAI Warmer Homes Scheme funds energy upgrades — including cavity wall insulation — in full for eligible homeowners, who pay nothing toward the qualifying works. It is well worth checking your eligibility before paying for a private installation.
Is your home suitable?
Not every cavity can be filled with standard methods. A surveyor will check:
- Cavity width — too narrow and beads won’t flow; very wide cavities may need a different product
- Render condition — cracked or failing external render lets water in and must be fixed first
- Exposure — homes on very exposed coastal sites may need partial fill or a water-repellent product to avoid rain tracking across the cavity
- Existing fill — many post-1990s homes are already insulated and don’t need anything
If standard fill isn’t suitable, the alternatives are internal dry-lining or external wall insulation — compare all options in our guide to wall insulation types.
Why start here
For homes with an unfilled cavity, cavity insulation is almost always the first wall measure to do: lowest cost, quickest job, no internal disruption, and a strong grant. Combine it with attic insulation for the two highest-value upgrades most homes can make.
Check whether you qualify for a grant or the free scheme: Check your SEAI eligibility or browse all our insulation guides.