Lets break it down.
Typical house extension cost per square metre in Ireland, including size, complexity and hidden cost drivers.
Cost per square metre (€/m²) spreads the total construction cost across the gross internal floor area of the extension.
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.
This distinction alone explains why €/m² figures online vary wildly.
Typically includes:
Foundations
Structure and external walls
Roof structure and covering
Windows and external doors
Basic internal finishes
Labour
Contractor overhead and margin
Not automatically included:
Kitchen supply
Flooring finishes
Professional fees
Planning costs
Utility upgrades
VAT (sometimes shown separately)
Below are realistic construction cost ranges for house extensions in Ireland based on current labour, material and compliance conditions.
Basic shell finish
Typical Cost per m² (Single Story)
€2,100 – €2,500
Typical Cost per m² (Two-Story)
€2,200 – €2,700
Standard finish
Typical Cost per m² (Single Story)
€2,600 – €3,200
Typical Cost per m² (Two-Story)
€2,400 – €3,000
High specification
Typical Cost per m²
€3,300 – €4,200
Typical Cost per m²
€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.
Why €/m² Can Be Misleading
• Structural steel quantities
• Extent of glazing
• Drainage relocation
• Site access difficulty
• Internal specification level
• Professional involvement
• VAT status
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.
Below we can see the Size vs Cost Efficiency – Larger extensions often reduce €/m² due to fixed costs being spread across more floor area.
Extension Size
20m²
Total Cost (Typical)
€65,000
Effective €/m²
€3,250
Extension Size
30m²
Total Cost (Typical)
€90,000
Effective €/m²
€3,000
Extension Size
40m²
Total Cost (Typical)
€115,000
Effective €/m²
€2,875
Why? Because preliminaries, mobilisation, design, and setup are not strictly linear with size.
Lets look at Regional Variations in Ireland and how rural builds may incur higher transport and access costs, reducing the gap.
Dublin & commuter belt
Highest Relative Cost
Cork, Galway, Limerick cities
Slightly lower
Rural areas
Lower labour costs but variable access
Pitfalls to watch out for
What Increases €/m² Above €4,000
• 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
What can Lower €/m² Below €2,500/m²
• 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.
VAT is frequently misunderstood so lets look at how VAT effects the cost per square meter?
If a contractor quotes:
€90,000 + VAT
(Then 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.
What are Professional Fees and how they can effect the overall cost of your project.
| 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 |
Typically additional to construction cost:
These costs should be added to total feasibility budgeting.
Now lets have a look at a Full Example Budget Scenario of a 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.
For most Irish households in 2026:
Summary: Realistic Budget Planning
A modest 25–35m² extension typically falls between
€85,000 and €140,000 total project cost
depending on specification and VAT.
Cost per square meter figures are useful as a starting point.
But total project budgeting must include:
• VAT
• Professional fees
• Fit-out
• Contingency Allowance of 5% – 10% (Ground risk and services relocation are the primary unknowns.)
Other resources:
Single vs Double Storey Extension Costs
Structural Steel and Foundation Costs
Timeline & Staged Payments Breakdown