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Extension Cost Calculator

See what your renovation could cost in 2026, with real Dublin and national pricing. Get an instant estimate, full house or room by room.

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25 m²

Add-ons

New kitchen included
+€15,000 – €40,000
New bathroom included
+€6,000 – €11,000

estimated construction cost

–

select options above

professional fees (est.)

–

architect, engineer, BER

contingency (15%)

–

recommended reserve, not part of build cost

suggested maximum budget

–

build + add-ons + fees + contingency

Select your extension type, area, location and finish above to see your estimate.

Cost breakdown

Typical additional costs not included above

Development levies (Dublin)€20 – €30 per m²
Individual RSJ beams€800 – €2,500 each

These figures are estimates for planning purposes only, including VAT at 13.5% on qualifying construction services. A written quote from a contractor who has visited your property is the only accurate figure. Small extensions carry large fixed costs — foundations, structural openings, roof integration, site setup — so a project under 40m² is priced with a minimum construction floor rather than a straight €/m² calculation, which would understate the true cost.

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How this price calculator works

This calculator uses build cost ranges by extension type, single-storey rear, single-storey side, two-storey, wrap-around or glazed/garden room, for Dublin and the rest of Ireland separately, adjusted by your chosen finish level. Figures include labour, materials and VAT at 13.5% on qualifying construction services, shown separately from professional fees and contingency rather than folded into one number.

For extensions under 40m², a minimum project cost applies instead of a straight per-square-metre calculation. Foundations, structural openings, roof integration and site setup cost roughly the same regardless of size, so a small extension priced purely by €/m² would understate the real cost – the calculator applies a realistic floor instead, which you’ll see flagged where it kicks in.

Kitchen and bathroom fit-outs, structural complexity and planning permission are shown as optional add-ons rather than baked into the headline number, so you can see exactly what’s driving your estimate. Planning status only adds a cost when you confirm permission is required, it isn’t assumed for you.

Frequently asked questions

Still have questions about your project? Call 01 270 9764 – we’ll be happy to help!

It gives a realistic planning range based on current Irish market rates and your specific inputs, not a fixed price. A written quote from a contractor who has visited the property is the only accurate figure for a specific project.

Extensions under 40m² still carry the full cost of foundations, structural openings, roof integration and site setup, which don't shrink in proportion to floor area. The calculator applies a minimum project cost so a small extension isn't underpriced by a straight €/m² calculation.

Not by default. These are optional add-ons you switch on, since not every extension includes a full kitchen or bathroom fit-out, and including them automatically would overstate the cost for those that don't.

Only if you select that planning permission is required. Whether it's needed depends on your specific design and location — the calculator doesn't assume this for you, and the allowance only applies once you've confirmed it.