How much does an extension cost in Ireland?
Reviewed October 2026 · Not legal, planning or financial advice
The figure quoted for a build — so many euro per square metre — is rarely what the project costs. Fees, engineering, surveys, contingency, a kitchen and external works routinely add a third or more. Here is how to think about the whole budget.
Construction cost per square metre
For a single-storey rear extension, ranges in the region of €2,300–€3,500 per m² including VAT at 13.5% are commonly cited in 2025–26, with typical projects around the middle. Side returns and wraparounds tend to cost more per m² (steelwork, party walls, glazed roofs); two-storey extensions tend to cost less per m² because foundations and roof serve two floors; attic conversions are usually cheapest per m².
These are indicative ranges, not tender prices. Specification, access, ground conditions and contractor workload move them significantly.
Dublin and regional differences
Construction in Dublin is generally dearer than the national average — around 10% in our model — reflecting labour costs, access and parking. Costs outside the main cities are typically somewhat lower. Treat any regional adjustment as approximate.
What the build price usually leaves out
- Architect or technologist fees for design and planning drawings — often 7–12% of construction.
- Structural engineer: steel beams, foundations, openings in rear or party walls.
- Measured survey, and possibly drainage survey.
- Planning application costs, or a Section 5 declaration.
- BCAR assigned certifier for extensions over 40m².
- Kitchen supply and fit — often €12,000–€35,000 on its own.
- Large sliding doors and rooflights beyond a standard specification.
- External works: drainage diversion, patio, boundary repair, landscaping.
- Contingency — 10–15% is prudent; more for older houses.
A worked example
A 22m² single-storey rear extension at a typical €2,800/m² is about €62,000 to build. Add fees, engineering, survey, a kitchen, external works and a 12% contingency, and the total project budget is closer to €100,000–€110,000. That is the number to plan around.
VAT
Construction services are generally charged at the reduced VAT rate (13.5%); professional fees at the standard rate (23%). Check how each quote treats VAT — some are quoted ex-VAT.
Getting to a real number
- Agree a brief and budget with your architect before design starts.
- Get the design priced by a quantity surveyor if the project is large.
- Tender the same drawings to at least three builders.
- Compare exclusions and provisional sums, not just the bottom line.
Regulations and their interpretation change. This guide explains the position as we understand it in October 2026. Confirm what applies to your house with an architect, planning consultant or your local authority before relying on it.