Wall insulation is the most impactful way to reduce your energy bills. Through the walls, an average home loses 20–30% of all heat. Well-insulated walls can save you €200–600 per year on heating costs, depending on the property and the current insulation situation. Costs for wall insulation vary greatly by method: from €15–25 per m² for cavity wall insulation to €80–150 per m² for external wall insulation. In this article you’ll find out which method is the best choice for your home, what the costs are and what grants are available.
What Does Wall Insulation Cost? DIY vs Hiring a Professional
Cost Overview
| Method | DIY per m² | Professional per m² | Typical house (60 m² wall) |
|---|---|---|---|
| Cavity wall insulation | Not possible (specialist work) | €15–25 | €900–1,500 |
| External wall insulation | Limited DIY possible | €70–150 | €4,200–9,000 |
| Internal wall insulation (plasterboard + insulation) | €15–30 | €40–70 | €900–1,800 (DIY) |
| Internal wall insulation (mineral wool + membrane) | €10–20 | €35–60 | €600–1,200 (DIY) |
Example calculation: cavity wall insulation for a mid-terrace house (60 m² external wall)
- Professional installation: approx. €900–1,500
- Payback period: 3–5 years
- Annual savings: approx. €200–350
When Is DIY Worth It?
Cavity wall insulation is specialist work (blown in under pressure) and cannot be done yourself. Internal wall insulation is excellent for DIYers: you fix insulation panels or mineral wool to the inside of the external wall and finish with plasterboard. External wall insulation requires scaffolding and experience — this is too complex for most DIYers.
Which Method Suits Your Home?
| House type | Recommended method | Reason |
|---|---|---|
| Cavity wall (built 1920–1980) | Cavity wall insulation | Cheapest, least disruptive |
| Cavity wall with narrow gap | Internal wall insulation | Cavity too narrow to fill |
| Pre-1920 house (solid wall) | Internal insulation or external | No cavity present |
| Flat (no external wall access) | Internal wall insulation | Can only be done from inside |
| Detached house, large façade | External wall insulation | Maximum insulation value |
How do you know if you have a cavity wall? For houses built after 1920, a cavity is almost always present. Check the wall thickness: a wall measuring 28–35 cm has a cavity. Thinner than 20 cm: solid wall, no cavity.
Method 1: Cavity Wall Insulation
What Is It?
Insulation material (glass wool, EPS/PIR beads or PU foam) is blown into the cavity from outside or inside. This requires specialised equipment and cannot be done yourself. After treatment, the drill holes (2–3 cm diameter) are neatly sealed.
Costs and Savings
| House type | Cost | Annual savings | Payback period |
|---|---|---|---|
| Mid-terrace house | €800–1,200 | €150–250 | 4–6 years |
| End-terrace house | €1,000–1,500 | €200–350 | 4–6 years |
| Detached house | €1,500–2,500 | €300–500 | 4–6 years |
Insulation Material Comparison
| Material | Rd-value | Advantages | Disadvantages |
|---|---|---|---|
| Glass wool (blown) | 1.5–2.5 | Inexpensive, fire-safe | Can settle (quality-dependent) |
| EPS beads | 2.0–3.0 | Stable, water-repellent | Slightly more expensive |
| PU foam | 2.5–4.0 | Highest insulation value | More expensive, less sustainable |
Method 2: External Wall Insulation
What Is It?
Insulation boards (EPS, mineral wool, PIR) are fixed to the outside of the wall and then finished with render or cladding. This is the most effective method but also the most expensive.
Costs and Savings
| Component | Price per m² |
|---|---|
| Insulation boards (EPS 100 mm) | €15–25 |
| Fixing system + adhesive | €10–15 |
| Reinforcement mesh + topcoat render | €25–40 |
| Labour costs (incl. scaffolding) | €30–60 |
| **Total per m²** | **€80–140** |
Advantage: Maximum insulation value (Rd 3.5–5.0), no loss of interior floor space, existing cold bridges are eliminated.
Disadvantage: High cost, the appearance of the external wall changes, planning permission sometimes required.
Method 3: Internal Wall Insulation (DIY)
What Is It?
The external wall is insulated from the inside. You build a frame of metal stud profiles or timber battens with insulation in between (mineral wool, glass wool or PIR boards), finished with plasterboard.
Step-by-Step Guide: Internal Wall Insulation
#### Step 1 — Prepare the Wall
Remove existing wall finishes where necessary. Check the wall for damp (a damp wall must be dried out first, otherwise the insulation will become wet). Apply a vapour control layer or vapour barrier to the wall (in cooler climates).
#### Step 2 — Fix Metal Stud or Timber Battens
Fix CW50 metal stud profiles or 4×5 cm timber battens to floor, ceiling and side walls, and every 60 cm. The depth of the frame determines the insulation thickness.
#### Step 3 — Install the Insulation
Place the insulation between the battens or studs. Cut mineral wool or PIR boards to size — they should fit snugly without being compressed (compression reduces the insulation value).
#### Step 4 — Vapour Control Layer
Apply a vapour control layer or vapour barrier across the entire wall. Tape all joints with vapour control tape. This prevents warm, humid indoor air from reaching the insulation and condensing.
#### Step 5 — Fix Plasterboards
Fix plasterboards (12.5 mm) to the frame. Finish the joints with scrim tape and joint compound (see article on fitting plasterboard).
Costs for DIY Internal Wall Insulation
| Material per m² | Price |
|---|---|
| Metal stud frame | €4–6 |
| Mineral wool (100 mm) | €6–10 |
| Vapour control layer + tape | €2–4 |
| Plasterboard (12.5 mm) | €5–8 |
| Finishing (filler, paint) | €3–5 |
| **Total per m²** | **€20–33** |
Grants for Wall Insulation (2026)
Energy Company Obligation (ECO) and Other Schemes
Various grant schemes are available to help offset the cost of wall insulation. Contact your energy supplier or local authority to find out what is available in your area.
| Insulation measure | Typical grant per m² |
|---|---|
| Cavity wall insulation | €7–12 per m² |
| External wall insulation | €18–27 per m² |
| Internal wall insulation | €6–9 per m² |
- Apply after the work has been completed
- Work must be carried out by an approved installer (for cavity wall and external insulation)
- Combining several measures may qualify you for additional low-interest or interest-free loans
Energy Rating Improvement
| Situation | Rating improvement |
|---|---|
| From G to F (wall only) | 1 step |
| From F to D (wall + roof) | 2–3 steps |
| From E to B (full package) | 3–4 steps |
Materials List for Internal Wall Insulation (15 m² wall)
| Material | Quantity | Estimated price |
|---|---|---|
| CW50 metal stud uprights | 7 pieces × 2.6 m | €40–55 |
| UW50 tracks (floor + ceiling) | 16 m | €25–35 |
| Mineral wool 100 mm | 15 m² | €60–90 |
| Vapour control membrane | 17 m² | €15–25 |
| Vapour control tape | 1 roll | €10–15 |
| Plasterboard 12.5 mm (moisture-resistant) | 13–14 sheets | €104–154 |
| Plasterboard screws, scrim tape, joint compound | 1 set | €25–35 |
| Acoustic sealant strip | 8 m | €6–10 |
Common Mistakes
| Mistake | Consequence | Solution |
|---|---|---|
| Insulating a damp wall | Moisture build-up, mould | Resolve the damp problem first |
| No vapour control layer | Condensation in insulation | Always fit a vapour barrier |
| Attempting DIY cavity wall insulation | Poor coverage, no guarantee | Leave this to a certified specialist |
| Not claiming a grant | Leaving money on the table | Always apply for available grants |
| Choosing insulation that is too thin | Insufficient insulation value | Minimum 80–100 mm for meaningful savings |
Conclusion
Wall insulation is one of the home improvement investments with the shortest payback periods. Cavity wall insulation is the cheapest and most effective choice if you have a cavity wall — don’t forget to apply for any available grants. No cavity, or want to work from the inside? Internal wall insulation is an excellent DIY project at around €20–33 per m². Always combine wall insulation with roof and floor insulation for maximum impact on your energy rating and monthly heating bills.
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