Typical house extension cost per square metre in Ireland, including detailed breakdowns by spec level, size, complexity and hidden cost drivers.
1. What “Cost per m²” Actually Means
Cost per square metre (€/m²) is a benchmarking tool, not a quote.
It spreads the total construction cost across the gross internal floor area of the extension.
It typically includes:
- Foundations
- Structure and external walls
- Roof structure and covering
- Windows and external doors
- Basic internal finishes
- Labour
- Contractor overhead and margin
It does not automatically include:
- Kitchen supply
- Flooring finishes
- Professional fees
- Planning costs
- Utility upgrades
- VAT (sometimes shown separately)
This distinction alone explains why €/m² figures online vary wildly.
2. Current Cost per m² Ranges in Ireland (2026)
Below are realistic construction cost ranges for house extensions in Ireland based on current labour, material and compliance conditions.
Standard Single Storey Extension
| Specification Level | Typical Cost per m² |
|---|---|
| Basic shell finish | €2,100 – €2,500 |
| Standard finish | €2,600 – €3,200 |
| High specification | €3,300 – €4,200 |
Two-Storey Extension
| Specification Level | Typical Cost per m² |
|---|---|
| Standard finish | €2,400 – €3,000 |
| High specification | €3,100 – €3,800 |
Two-storey extensions often show a lower €/m² figure because:
- Roof cost is spread over double floor area
- Foundations are shared
- Scaffolding is already required
However, total project cost is obviously higher.
3. Why €/m² Can Be Misleading
Two projects both quoted at €3,000/m² can differ by tens of thousands of euro.
Because €/m² ignores:
- Structural steel quantities
- Extent of glazing
- Drainage relocation
- Site access difficulty
- Internal specification level
- Professional involvement
- VAT status
The figure is useful for early feasibility, but not for contract comparison.
4. Cost Breakdown by Component (Per m² Equivalent)
The following table converts a typical €3,000/m² extension into proportional cost categories.
Example Cost Distribution (Standard Finish, €3,000/m²)
| Cost Category | % of Total | Approx €/m² Equivalent |
|---|---|---|
| Foundations & groundworks | 15% | €450 |
| Structure & walls | 20% | €600 |
| Roof | 10% | €300 |
| Windows & doors | 12% | €360 |
| First fix (plumbing & electrics) | 10% | €300 |
| Plastering & finishes | 10% | €300 |
| Internal carpentry | 8% | €240 |
| Contractor overhead & margin | 10% | €300 |
| Contingency allowance | 5% | €150 |
This distribution varies significantly by project.
5. Size vs Cost Efficiency
Larger extensions often reduce €/m² due to fixed costs being spread across more floor area.
Example Comparison
| Extension Size | Total Cost (Typical) | Effective €/m² |
|---|---|---|
| 20m² | €65,000 | €3,250 |
| 30m² | €90,000 | €3,000 |
| 40m² | €115,000 | €2,875 |
Why?
Because preliminaries, mobilisation, design, and setup are not strictly linear with size.
6. Regional Variations in Ireland
Costs are typically:
| Region | Relative Cost |
|---|---|
| Dublin & commuter belt | Highest |
| Cork, Galway, Limerick cities | Slightly lower |
| Rural areas | Lower labour costs but variable access |
However, rural builds may incur higher transport and access costs, reducing the gap.
7. What Increases €/m² Above €4,000
Extensions exceed €4,000/m² when:
- Large structural openings require multiple steel beams
- High-performance glazing is specified
- Underfloor heating is included
- Complex roof forms are used
- Extensive landscaping/reinstatement required
- High-end internal finishes are included in build contract
8. What Lowers €/m²
Lower figures (under €2,500/m²) typically assume:
- Basic internal finish
- No kitchen included
- Minimal glazing
- Straightforward ground conditions
- Limited services relocation
These figures should not be assumed for turnkey kitchen/dining extensions.
9. VAT and €/m²
VAT is frequently misunderstood.
If a contractor quotes:
€90,000 + VAT
The effective €/m² changes materially.
Example:
30m² extension at €90,000 excl VAT
= €3,000/m²
Including 13.5% VAT:
€102,150
= €3,405/m² effective
This must be considered when comparing figures.
10. Professional Fees (Not Included in €/m²)
Typically additional to construction cost:
| Professional | Typical Range |
|---|---|
| Architect / technologist | €4,000 – €12,000 |
| Structural engineer | €1,500 – €4,000 |
| Assigned certifier (if required) | Project dependent |
| Planning drawings & application | €1,500 – €3,500 |
These costs should be added to total feasibility budgeting.
11. Contingency Allowance
A prudent contingency allowance for extensions is:
5% – 10%
Ground risk and services relocation are the primary unknowns.
12. Example Full Budget Scenario
30m² Standard Kitchen Extension
| Item | Cost |
|---|---|
| Construction (30 × €3,000) | €90,000 |
| VAT (13.5%) | €12,150 |
| Architect & engineer | €7,500 |
| Planning costs | €2,000 |
| Contingency (7%) | €6,300 |
| Total Estimated Project Budget | €117,950 |
This excludes kitchen supply.
13. Summary: Realistic Budget Planning
For most Irish households in 2026:
- A modest 25–35m² extension typically falls between
€85,000 and €140,000 total project cost
depending on specification and VAT.
€/m² figures are useful as a starting point.
But total project budgeting must include:
- VAT
- Professional fees
- Fit-out
- Contingency
14. Other resources:
Single vs Double Storey Extension Costs
Structural Steel and Foundation Costs
Timeline & Staged Payments Breakdown