How Much Does a House Extension Cost in Ireland in 2025?
A house extension is often cheaper than moving — but it's still a major investment. Irish homeowners typically spend between €40,000 and €150,000 depending on size and spec.
Here's what you need to budget for.
Quick Answer: Extension Costs per Square Metre
| Budget/basic | €1,800 - €2,200 |
| Architect-designed | €4,500 - €6,000+ |
These are total costs including structure, fit-out, fees, and finishes.
Real Examples
| Extension Type | Size | Total Cost |
| Single-storey rear | 20m² | €45,000 - €65,000 |
| Single-storey rear | 40m² | €80,000 - €120,000 |
| Two-storey side | 50m² | €100,000 - €150,000 |
| Sunroom/garden room | 15m² | €25,000 - €40,000 |
| Attic conversion | 25m² | €30,000 - €50,000 |
| Garage conversion | 20m² | €15,000 - €30,000 |
Cost Breakdown
Structure & Build (60% of budget)
| Foundations | €8,000 - €15,000 |
| Windows & doors | €5,000 - €15,000 |
| Structural steel | €3,000 - €8,000 |
First Fix (15% of budget)
| Plumbing first fix | €2,000 - €5,000 |
| Electrical first fix | €2,000 - €4,000 |
| Insulation | €2,000 - €4,000 |
| Plastering | €3,000 - €6,000 |
Second Fix & Fit-Out (20% of budget)
| Plumbing second fix | €1,500 - €3,000 |
| Electrical second fix | €1,500 - €3,000 |
| Kitchen (if applicable) | €8,000 - €25,000 |
| Bathroom (if applicable) | €5,000 - €15,000 |
Professional Fees (5-15% of budget)
| Architect (design) | €3,000 - €10,000 |
| Planning application | €80 - €130 |
| Building control (commencement) | €60 |
| Building control (completion) | €30 |
| Assigned certifier | €2,000 - €4,000 |
| Energy rating (BER) | €150 - €300 |
Do I Need Planning Permission?
Exempt Development (No planning needed)
You can build without planning if:
- Extension is at rear of house
- Not more than 40m² (semi-d/terrace) or 20m² (detached)
- Not higher than eaves of existing house
- Doesn't reduce private garden below 25m²
- Not within 2m of boundary (if over single storey)
Planning Required
You need planning if:
- Front extension (almost always)
- Exceeds size limits above
- Protected structure or ACA area
Planning fee: €80 (standard) to €130 (retention)
Timeline: 8-12 weeks for decision
Building Regulations
Every extension needs to comply with Building Regulations (Part L energy, Part M access, etc.).
You need:
- Design certifier (architect/engineer)
- Assigned certifier (inspects during build)
- Commencement notice (before starting)
- Certificate of compliance (after completion)
Cost: €3,000 - €8,000 for all certifications
How to Save Money
1. Keep It Simple
Flat roof cheaper than pitched. Square plan cheaper than L-shaped.
2. Stay Under Exempt Limits
40m² rear extension = no planning fees or delays.
3. Use Standard Sizes
Off-the-shelf windows and doors are cheaper than custom.
4. Get 5+ Quotes
Builder prices vary by 30-50% for the same spec.
5. Do Some Work Yourself
- Landscaping: Save €2,000+
6. Avoid Winter Starts
Bad weather = delays = cost overruns.
Timeline: How Long Does an Extension Take?
| Planning (if needed) | 8-12 weeks |
| Tender & select builder | 2-4 weeks |
| Groundwork & foundations | 2-3 weeks |
| Structure & roof | 4-6 weeks |
| Second fix & fit-out | 3-4 weeks |
Finding a Builder
Get recommendations from:
- Neighbours who've had work done
- Architects (they know who does good work)
- Online directories with verified reviews
Questions to ask:
1. Can I see completed extensions?
2. Are you VAT registered?
3. Do you have insurance?
4. Will you provide a fixed-price contract?
5. What deposit do you require?
6. What's your current availability?
Red flags:
- Can start immediately (why aren't they busy?)
Contract Essentials
Your building contract should include:
- Fixed price or schedule of rates
- Start and completion dates
- Payment schedule (linked to milestones)
- Retention clause (hold back 5% for 6 months)
- Specification of all work
- Who provides what (materials, skips, etc.)
Is an Extension Worth It?
Generally, extensions add value — but not always €1 for €1.
| Extension Type | Value Added |
| Extra bedroom | 70-100% of cost |
| Extra bathroom | 60-80% of cost |
| Kitchen extension | 50-80% of cost |
Best ROI: Adding a bedroom + bathroom to a 2-bed house.
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Looking for builders? Find rated builders near you on TradesmenIreland.ie.