Internal wall insulation — also called dry-lining — typically costs €3,500–€8,000 for a semi-detached Irish home before the SEAI grant. It is the lower-cost way to insulate solid or hard-to-treat walls, but it trades floor space and detailing risk for that saving.
What is internal dry-lining?
Dry-lining fixes insulation to the inside face of your external walls. There are two common approaches:
- Insulated plasterboard (“bonded board”) — boards of rigid insulation backed with plasterboard, dot-and-dabbed or fixed to the wall.
- Framed (battened) system — a timber or metal frame holds insulation between studs, with a vapour layer and plasterboard over it.
It is the main option for solid stone or single-skin walls where there is no cavity to fill, and for individual rooms where external work is not practical.
Internal wall insulation cost
Typical installed costs in Ireland, before grant:
| Dwelling | Typical installed cost (before grant) |
|---|---|
| Apartment / single room | €1,500–€3,500 |
| Mid-terrace | €3,000–€6,000 |
| Semi-detached | €3,500–€8,000 |
| Detached | €6,000–€12,000 |
The figures rise with wall area and with the amount of “making good” needed — moving skirting boards, electrical sockets, radiators, and door frames, then redecorating. These are contractor estimates, so get three written quotes from SEAI-registered installers.
SEAI grants for internal insulation
Grants are set by dwelling type and paid after the work is completed and inspected:
| Dwelling | Grant |
|---|---|
| Detached | €4,500 |
| Semi-detached / end-terrace | €3,500 |
| Mid-terrace | €2,000 |
| Apartment | €1,500 |
As with all SEAI insulation grants, the home must pre-date the relevant cut-off, the work must be carried out by a registered contractor, and a post-works BER is required. The insulation grants guide covers the conditions in full.
Room-size loss
The biggest practical downside is space. A dry-lining build-up adds roughly 60–100mm to each treated wall. In a 3m × 3m room treated on two external walls, that can remove a noticeable slice of floor area and means windows sit in deeper reveals. Confirm the exact build-up with your installer before committing, especially in small bedrooms and bathrooms.
Rooms also need to be cleared and redecorated, and the work is done from inside — so it is more disruptive room-by-room than cavity fill or external insulation.
Condensation and detailing risk
Because internal insulation keeps the original wall cold, moisture management matters more than with other methods. Risk points include:
- Junctions where internal walls and floors meet the external wall — these can stay cold and form thermal bridges
- Embedded timbers and joist ends in older walls, which need ventilation to avoid trapped moisture
- The vapour layer, which must be continuous and sealed around sockets, pipes, and openings
A competent installer designs for these. Cutting corners here is the main reason poorly executed dry-lining leads to mould and damp.
Internal vs external — which to pick?
| Internal (dry-lining) | External (EWI) | |
|---|---|---|
| Cost | Lower | Higher |
| Room size | Reduced | Unchanged |
| Thermal bridges | Harder to eliminate | Largely eliminated |
| Disruption | Per-room, internal | Mostly external |
| Exterior appearance | Unchanged | Changed |
If your priority is the best thermal result and you can fund it, compare with external wall insulation cost. For a full side-by-side of all three approaches, see our guide to wall insulation types. And if your walls actually have an unfilled cavity, start with the cheaper cavity wall insulation instead.
Want to know which measures your home qualifies for? Check your SEAI grant eligibility or explore all our insulation guides.