How much does a house extension cost in Ireland?
A house extension in Ireland typically costs €2,500–€4,000 per square metre for a good-quality build in 2026, so a 30 m² single-storey extension often lands between €75,000 and €120,000 once fully finished. Costs vary widely with specification, site conditions and location.
This guide explains how extensions are priced, what's included, when you need planning permission and how to keep the budget under control.
Typical extension costs in Ireland (2026)
| Job | Typical price |
|---|---|
| Basic build (per m²) | €2,200 – €2,800 |
| Mid-range build (per m²) | €2,800 – €3,500 |
| High-spec build (per m²) | €3,500 – €4,500 |
| 30 m² single-storey extension | €75,000 – €120,000 |
| Two-storey extension (per m²) | €2,500 – €3,800 |
| Architect / design fees | 7% – 12% of build cost |
Prices are typical 2026 estimates and vary by job, condition and location.
What's included in the cost per m²?
A per-square-metre figure usually covers the structural build — foundations, walls, roof, windows, doors and basic internal finishes. Kitchens, bathrooms, high-end flooring, bespoke joinery and landscaping are typically extra, so always check what a quote does and doesn't include.
Do you need planning permission?
Many single-storey rear extensions fall under exempted development if they're below the floor-area limit and meet conditions on height and boundaries. Larger extensions, two-storey builds or work to protected structures usually need full planning permission. Always confirm with your local authority or architect before starting.
Budgeting for the whole project
- Add 10–15% contingency for surprises once work starts.
- Budget design and engineering fees (often 7–12% of the build).
- Allow for planning fees, surveys and BER assessment.
- Remember finishes — kitchen, bathroom, flooring — are often separate.
How to keep costs down
- Keep the shape simple — complex rooflines and angles cost more.
- Get a detailed, fixed-price quote from a reputable builder.
- Avoid changing the design once work has started.
- Compare at least three builders and check references.
Frequently asked questions
How much does an extension cost per square metre in Ireland?+
Expect roughly €2,500–€4,000 per square metre in 2026 for a good-quality build, more for high-spec finishes and tricky sites.
How much does a 30 m² extension cost in Ireland?+
A fully finished 30 m² single-storey extension typically costs €75,000–€120,000, depending on specification and location.
Do I need planning permission for an extension?+
Many small single-storey rear extensions are exempt if they stay within the floor-area and height limits, but larger or two-storey extensions usually need planning permission. Check with your local authority first.
How long does an extension take to build?+
A typical single-storey extension takes around 3–5 months on site, plus design and planning time beforehand.
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