House extension guides and cost planner
Building on one level costs €1,500 to €2,200 per m² across Ireland, and building two storeys €2,000 to €2,500 per m² with both floors counted, VAT at 13.5% included. Dublin and the commuter counties sit higher. With design and engineer's fees, a 20 m² ground-floor room comes to €42,000 to €54,000 and a 40 m² two-storey extension with an en-suite to €105,000 to €128,000.
Every cost guide, extension type, planning rule, building control guide and county page in one place.
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- 45 m²exempt behind the house
- €1,500–€2,200per m², one storey
- 13.5%VAT on the build
- 26counties covered
Every way to extend a house
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.
Two-storeyTwo new floors in one build: more living space downstairs and an extra bedroom over it.
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.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.
25 m² single-storey rear, mid-range finish: €52,000 to €65,000, 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.
Cost, planning, building regulations and finance guides
Common house extension questions
How much does a house extension cost in Ireland?
Building on one level costs €1,500 to €2,200 per m² across Ireland, and building two storeys €2,000 to €2,500 per m² with both floors counted, VAT at 13.5% included. Dublin and the commuter counties sit higher. With design and engineer's fees, a 20 m² ground-floor room comes to €42,000 to €54,000 and a 40 m² two-storey extension with an en-suite to €105,000 to €128,000.
Can I extend without planning permission?
Since 27 July 2026 you can build up to 45 m² behind the house without applying for planning permission. That 45 m² includes every extension added since 1964 and any attached garage you convert. The extension can't rise above the house, the house has to keep 25 m² of private open space, ground-floor windows need 1 m or more to the boundary they look onto, and no more than 12 m² of it can be upstairs on a semi or terrace (20 m² on a detached house). Before that date the limit was 40 m².
Is it cheaper to extend or move?
Moving costs money that buys no extra room. On a €380,000 house, the median people moving home paid in 2025, stamp duty on the next house is €3,800, the agent's fee on the sale is €4,700 to €11,700 with VAT and the solicitor €2,000 to €5,000: €10,500 to €20,500 before removals, and before the higher price of a bigger house. Extending keeps all of it in the house you already own.
What VAT is charged on an extension?
13.5% on the building work and on fixtures the builder supplies and fits. 23% on appliances, professional fees, and fixtures you buy yourself.
Every guide, calculator and county page
Jump straight to any specification guide, our interactive calculator, the technical glossary or your county page.
Price & Specification Guides
Calculator, FAQ & Glossary
Room to grow, without moving
Pick the type, the size and the finish to see the cost in your county. When you want a firm price, your plan goes to a single vetted builder for your area.