Two-storey extensions
A two-storey extension costs €2,000 to €2,500 per m² across Ireland and €2,200 to €2,800 in Dublin, VAT included, measured over both floors. Per m² it is the lowest-cost new floor area you can build, because the two floors share one set of foundations and one roof. Most need planning permission, because only 12 m² upstairs is exempt on a semi-detached or terraced house, and 20 m² on a detached one.
Living space below and a bedroom above: what it costs, why it costs less per m², and the planning it nearly always needs.
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- €2,000–€2,500per m², both floors, VAT in
- 12 m²exempt upstairs on a semi or terrace
- 8 mfrom an upstairs window to the boundary
- 14–24 weeksof building
Cost by size
National rates, mid-range, VAT and fees included. Dublin and the commuter counties sit higher.
| Both floors | Mid-range, with fees | With an en-suite upstairs |
|---|---|---|
| 24 m² (12 m² a floor) | €59,000 to €70,000 | €69,000 to €88,000 |
| 32 m² (16 m² a floor) | €77,000 to €90,000 | €87,000 to €108,000 |
| 40 m² (20 m² a floor) | €95,000 to €110,000 | €105,000 to €128,000 |
| 50 m² (25 m² a floor) | €118,000 to €135,000 | €128,000 to €153,000 |
| 60 m² (30 m² a floor) | €140,000 to €160,000 | €150,000 to €178,000 |
The en-suite column adds a shower room upstairs fitted out at a mid-range level, €10,000 to €18,000.
Why two floors cost less per m²
Foundations and the roof are two of the dearest parts of any extension. On a two-storey extension they serve twice the floor area. That's why the two-storey rate is €2,000 to €2,500 per m² while one storey is €1,500 to €2,200, and why a family that needs a bedroom and a bigger ground floor usually gets both for less than two separate jobs would cost.
The stairs normally don't move. The new upstairs room opens off the existing landing, often through what was a window or the end of the landing.
Plan your house extension
Four quick taps, and your plan fills in as you answer: what it costs, whether it needs planning permission and how long it takes. Contact details come last, and only if you want a builder to price it.
40 m² two-storey, mid-range finish: €95,000 to €110,000, including VAT and fees.
How the estimate is worked out
Every kind of extension has a build rate per m² for each region of Ireland, VAT at 13.5% included. A standard finish uses the lower half of that range and mid-range the upper half; high spec or a wall of glass moves the build to the glazed rate. Design, engineer and BER fees go on top, with anything you tick (an en-suite, a kitchen, a steel beam into the house) priced at your finish. A garage conversion gets one price for the whole job, since the walls and roof are already standing. Totals are rounded to the nearest €1,000. Use it to plan with. It isn't a quote: a builder prices your house after seeing it.
Planning: the upstairs rules
The exemption barely reaches upstairs: 12 m² of floor above ground level on a semi or terrace and 20 m² on a detached house, kept 2 m from any party boundary, and every upstairs window needs 8 m to the boundary opposite. Both floors count towards the 45 m² in total.
So most two-storey extensions need planning permission. Newspaper and site notices, drawings, €34 to the council, 8 weeks for the decision and 4 weeks for appeals. Planning permission for a house extension.
Building it
14 to 24 weeks of building. The ground floor goes up first, then the upper floor and the roof, then the new rooms are opened into the house: downstairs through the back wall, upstairs off the landing. The scaffolding stays up for most of the job.
With planning permission, a commencement notice goes to the council 14 to 28 days before work starts. Above 45 m², certifiers sign the work off, unless the owner opts out. Building regulations.
Other ways to extend
Each has its own page: costs by size, the planning rules that apply and the weeks of building.
Single-storey rearOne new room behind the house at ground level: a family room, a playroom or a bedroom for a parent.
Side extensionThe strip beside a semi or detached house, built on at one level or two.
WraparoundAn L round the back corner of the house, for one big room with a utility or toilet off it.
Garage conversionThe garage you already have becomes a bedroom, an office or a playroom.
Bedroom and en-suiteOne more bedroom, downstairs or up, with a shower room of its own.Questions before you build
How much does a two-storey extension cost in Ireland?
A two-storey extension costs €2,000 to €2,500 per m² across Ireland and €2,200 to €2,800 in Dublin, VAT included, measured over both floors. Per m² it is the lowest-cost new floor area you can build, because the two floors share one set of foundations and one roof. Most need planning permission, because only 12 m² upstairs is exempt on a semi-detached or terraced house, and 20 m² on a detached one.
Does a two-storey extension need planning permission?
Nearly always. Only 12 m² upstairs is exempt on a semi or terrace (20 m² detached), set 2 m in from any party boundary, with upstairs windows 8 m back from the boundary opposite.
Is a two-storey extension cheaper than a single storey?
Each m² costs less, €2,000 to €2,500 against €1,500 to €2,200, because the two floors share the foundations and the roof. The total is higher, because you get twice the room.
How long does a two-storey extension take?
14 to 24 weeks of building, after 8 to 16 weeks of design and pricing and about 12 weeks for planning permission.
Can the stairs stay where they are?
Usually. The upstairs room opens off the existing landing, so the stairs don't move.
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