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A realistic budget for your extension in about a minute, with 2026 prices for Dublin and the rest of Ireland. Includes VAT, fees and a contingency.
These are the build rates the calculator uses, per square metre at a standard finish, including labour, materials and VAT at 13.5%. Dublin costs more because labour, waste and site access cost more.
A basic finish brings the rate down by about 18%. A high-spec finish, with large glazing and premium materials, adds about 30%.
| Extension type | Dublin | Rest of Ireland |
|---|---|---|
| Single-storey rear | €2,700 to €3,400 | €2,400 to €3,000 |
| Single-storey side | €2,800 to €3,500 | €2,500 to €3,100 |
| Two-storey rear | €2,200 to €3,100 | €1,900 to €2,700 |
| Wrap-around | €3,100 to €4,000 | €2,800 to €3,600 |
| Glazed / garden room | €3,400 to €4,500+ | €3,000 to €4,000+ |
Per m², standard finish, including VAT. Professional fees and contingency come on top.
Foundations, knocking through the back wall, tying the roof in and setting up the site cost about the same whether you add 12 m² or 30 m². So below 40 m², a simple per m² sum makes a small extension look cheaper than it is. The calculator uses these minimum build costs instead.
| Floor area | Dublin | Rest of Ireland |
|---|---|---|
| Up to 15 m² | €40,000 to €58,000 | €35,000 to €50,000 |
| Up to 20 m² | €46,000 to €69,000 | €40,000 to €60,000 |
| Up to 30 m² | €58,000 to €98,000 | €50,000 to €85,000 |
| Up to 40 m² | €80,000 to €138,000 | €70,000 to €120,000 |
Minimum build cost including VAT, before fees and contingency. Above 40 m² the per m² rate takes over.
Three common extensions run through the calculator. These are Build Me estimates to show how the numbers add up, not prices from finished jobs.
20 m² single-storey rear, standard finish, new kitchen, exempt from planning.
Total budget
€85,000 to €134,000
35 m² wrap-around, standard finish, several openings, planning needed.
Total budget
€141,000 to €192,000
40 m² two-storey rear, standard finish, new bathroom upstairs, planning needed.
Total budget
€104,000 to €170,000
Optional extras the calculator can add: a new kitchen (€15,000 to €40,000), a new bathroom (€7,000 to €13,000 in Dublin), more complex structural work (€3,000 to €8,000, or €8,000 to €20,000 for heavy steel) and planning with drawings (€1,500 to €4,000).
Since 27 July 2026, a rear extension can be exempt from planning if all the extensions built on the house since 1964 come to 45 m² or less, up from 40 m². Upstairs, the limit is 12 m² on a terraced or semi-detached house and 20 m² on a detached house, and at least 25 m² of garden has to stay.
Side extensions, and front extensions other than a small porch, need planning permission. If yours does, pick “Needed” in the calculator to add drawings and fees, and allow 12 to 16 weeks from drawings to a decision. Our planning permission guide covers every rule.
It multiplies your floor area by the rate for your extension type and location, then adjusts it for the finish you pick. For extensions of 40 m² or less it checks the result against a minimum build cost and uses whichever is higher.
Professional fees are added at 10 to 12% of the build cost, and a 15% contingency on top of the build and extras. A kitchen, bathroom, structural work and planning only count when you switch them on, so you can see exactly what moves the number.
An online estimate gets your budget right. A visit gets the price right, because the details that change a price only show up on site.
Use the calculator to set a realistic budget before you speak to anyone.
We visit, look at the house and talk through what you want.
A detailed quote in writing, with materials and every trade listed.
Managed by one team from start to finish.
Still have questions about your extension? Call 01 270 9764 and we’ll be happy to help.
It gives a realistic budget range from current Irish build rates and your answers, not a fixed price. Drains, ground conditions and the state of the existing walls only show up on site, so a written quote after a visit to your home is the only accurate figure for your project.
A 20 m² single-storey rear extension in Dublin at a standard finish has a build cost of about €54,000 to €69,000 including VAT. With professional fees and a 15% contingency, budget about €68,000 to €88,000. Outside Dublin the build cost is about €48,000 to €60,000.
At a standard finish, including VAT, a single-storey rear extension costs about €2,700 to €3,400 per m² in Dublin and €2,400 to €3,000 per m² in the rest of Ireland. Two-storey extensions cost less per m², about €2,200 to €3,100 in Dublin, because the foundations and roof are shared across two floors.
Extensions of 40 m² or less still carry the full cost of foundations, knocking through, tying in the roof and setting up the site, which don't shrink in proportion to the floor area. The calculator uses a minimum build cost so a small extension isn't underpriced by a straight per m² sum.
Yes. The build rates include VAT at 13.5% on the construction work. Professional fees and the contingency are shown as separate lines.
Not unless you switch them on. Not every extension needs a full kitchen or bathroom, so adding them by default would overstate the cost. A new kitchen adds €15,000 to €40,000 and a new bathroom €7,000 to €13,000 in Dublin.
Only if you pick “Needed”. Many rear extensions up to 45 m² in total are exempt, so the calculator doesn't assume you need planning. When you do, it adds €1,500 to €4,000 for drawings and planning fees.
Development levies (about €20 to €30 per m² in Dublin), extra steel beams beyond the usual (€800 to €2,500 each), furniture and landscaping. The 15% contingency is there for surprises found once work starts.