Extension Costs Ireland: What to Budget in 2026

Building an extension is one of the biggest investments you'll make in your home. With construction costs fluctuating in Ireland, knowing what to budget in 2026 helps you plan realistically and avoid nasty surprises.

Average Extension Costs in Ireland 2026

The cost per square metre for a house extension in Ireland typically ranges from €2,200 to €3,500, depending on the specification and location. Dublin and surrounding counties tend to be at the higher end.

Extension Types & Typical Costs

Single-Storey Rear Extension

The most common extension type in Ireland. Perfect for expanding your kitchen or adding an open-plan living area.

Two-Storey Extension

More cost-effective per square metre than single-storey because you're sharing foundations and roof costs. Typically adds bedrooms upstairs with living space below.

Side Return Extension

Popular for Victorian and Edwardian terraced houses. Opens up the kitchen into the side passage.

Sunroom / Garden Room

A more affordable option if you want extra living space. Less complex construction but still requires proper foundations.

What's Included in Extension Costs?

A typical extension quote should include:

• Foundations and groundworks
• Structural work (walls, steels, roof)
• Insulation to current Building Regulations
• Windows and external doors
• First-fix electrics and plumbing
• Plastering and painting
• Flooring (often basic)
• Connection to existing house

Additional Costs to Budget For

Planning Permission in Ireland

Many extensions can be built under exempted development rules (no planning required), but there are strict limits:

• Maximum 40 sqm for a single-storey rear extension
• Must not exceed the height of the existing house
• Cannot reduce garden space below 25 sqm
• Side extensions have stricter limits (typically 12 sqm)

Always verify with your local planning authority. If your property is in an architectural conservation area or is a protected structure, planning permission is almost always required.

What Affects Extension Costs?

• Location: Dublin costs 10-20% more than rural areas
• Access: Difficult access increases labour and material delivery costs
• Ground conditions: Poor soil may need deeper/wider foundations
• Specification: Premium finishes add significantly to cost
• Existing structure: Older homes may need structural upgrades
• Market conditions: Builder availability affects pricing

Timeline: How Long Does an Extension Take?

• Design and planning: 2-6 months
• Getting quotes and selecting builder: 1-2 months
• 20-30 sqm single-storey: 10-14 weeks
• 40-50 sqm single-storey: 14-18 weeks
• Two-storey extension: 16-24 weeks

How to Keep Costs Down

1. Simple design: Rectangular extensions cost less than complex shapes
2. Flat roof: Cheaper than pitched, though pitched lasts longer
3. Standard materials: Bespoke items cost significantly more
4. Off-peak timing: Winter builds may get better rates
5. Act as project manager: Source materials yourself if you have time
6. Phase the work: Do basics now, upgrade finishes later

Finding the Right Builder

Your extension builder should:

• Be registered with the Construction Industry Register Ireland (CIRI)
• Have public liability and employer's liability insurance
• Provide references from similar projects
• Offer a detailed, itemised quote
• Have clear payment terms (never pay more than 10% upfront)
• Be willing to work with your architect/engineer

Red Flags to Watch For

• Asking for large deposits upfront (more than 10%)
• No written contract or vague scope of work
• Quote significantly lower than others (corners will be cut)
• Reluctant to provide insurance certificates
• No fixed address or professional presence
• Pressure to sign quickly