House Extension Cost Ireland 2026: The Complete Guide
Adding a house extension is one of the best ways to gain extra living space without the high costs, stress, and stamp duty associated with selling and moving. In 2026, building material costs, building regulations, and contractor demand have stabilized, but pricing remains substantial.
1. Typical Extension Costs (Per Square Metre)
Average extension costs in Ireland in 2026 range from €2,100 to €3,200 per square metre (or €195 to €300 per sq. ft.) depending on the extension style, height, and materials used.
| Extension Type | Average Cost (per sqm) | Typical Project Budget (40sqm) |
|---|---|---|
| Single-Storey Flat Roof (EPDM/GRP) | €2,100 – €2,600 | €84,000 – €104,000 |
| Single-Storey Pitched Roof (Tiles/Slate) | €2,300 – €2,850 | €92,000 – €114,000 |
| Double-Storey Extension | €2,600 – €3,200 | €104,000 – €128,000+ |
This means a standard 40 square metre (approx. 430 sq. ft.) ground-floor rear extension will cost between €84,000 and €114,000 turnkey using a main contractor, depending on finish.
2. Planning Permission Rules in Ireland
One of the main advantages of extending your home is that many projects are exempt from planning permission under Irish Planning Regulations. You do not need planning permission for an extension provided you meet these conditions:
- The extension is located to the **rear** of the house.
- The floor area of the extension does not exceed **40 square metres** (cumulative of all extensions added to the property since construction).
- For a terraced or semi-detached house, the extension is single-storey and does not exceed the height of the existing roof line.
- You leave at least **25 square metres** of private, open garden space.
3. Key Hidden Costs to Anticipate
- Structural Steel (RSJs): Creating an open-plan layout connecting your kitchen to the new extension requires steel beams to support the upper floor, costing €2,500 to €6,000.
- Drains and Manhole Relocation: If the extension covers existing sewer pipes or inspection chambers, they must be redirected or sealed with airtight double-seal covers, adding €1,500 to €3,500.
- Plumbing and Boiler Upgrades: Adding radiators or underfloor heating to the new extension may require a boiler upgrade or a zoning system to comply with building regulations.