How much does a house extension cost in Ireland in 2026?

As an indicative 2026 range, a finished single-storey extension costs roughly €2,500–€4,000 per square metre, so a 20 m² ground-floor extension works out around €55,000–€90,000. Two-storey extensions are typically €2,200–€3,200 per m². Planning, architect and engineer fees are extra. Always get at least three written quotes.

Do I need planning permission for an extension in Ireland?

Many single-storey rear extensions are exempt from planning permission if they stay within the limits set out in the planning regulations, including a floor-area limit of 40 m² for the extension (with conditions on how much can be to the rear and remaining private open space). First-floor and front extensions usually need permission. Always confirm with your local authority or an architect before building.

Is a two-storey extension cheaper per m² than single-storey?

Yes, usually. A two-storey extension shares one foundation and one roof across two floors, so the cost per square metre (around €2,200–€3,200 indicatively) is often lower than a single-storey extension (€2,500–€4,000 per m²). It does need planning permission and adds structural complexity.

What extra fees come with an extension?

Beyond the build cost, budget for architect or designer fees, structural engineer fees, an assigned certifier under Building Control regulations where required, planning application fees if not exempt, and connections or services. These professional fees commonly add 10–15% to the project.

How much does a kitchen extension cost in Ireland?

A 20 m² single-storey rear kitchen extension typically costs around €55,000–€90,000 for the finished build (indicative 2026 range), before kitchen units and appliances. With a mid-range fitted kitchen the all-in figure is usually €70,000–€110,000+, depending on glazing and finish. Always get at least three written quotes.

Why is a side return extension so expensive per square metre?

A side return or infill extension is small but has a lot of foundations, roof and glazing relative to its floor area, and it's usually built on a tight terraced site with difficult access. That pushes the cost per m² (around €2,800–€4,500 indicatively) above a simple rear extension, even though the total bill is lower because the floor area is small.

Is VAT charged on a house extension in Ireland?

Yes. Construction services in Ireland are charged at the reduced 13.5% VAT rate rather than the 23% standard rate. Check whether quotes are VAT-inclusive so you're comparing like for like, and use a tax-compliant contractor.

renovation

House Extension Cost Ireland 2026 (Per m² Price Guide)

What a house extension costs in Ireland in 2026: per-m² prices, worked examples, the 40 m² exemption, architect and engineer fees, and how to upgrade BER.

23 June 2026

House Extension Cost Ireland 2026 (Per m² Price Guide)

A finished single-storey house extension in Ireland costs roughly €2,500–€4,000 per square metre (indicative 2026 range), so a 20 m² ground-floor extension typically lands around €55,000–€90,000. Two-storey extensions are usually cheaper per m² at around €2,200–€3,200. Planning, architect and engineer fees are extra.

Extension cost by type and size

Extension type	Indicative 2026 cost per m²	Worked example
Single-storey rear, finished	€2,500–€4,000	20 m² ≈ €55,000–€90,000; 30 m² ≈ €75,000–€120,000
Side return / infill, single-storey	€2,800–€4,500	12 m² ≈ €34,000–€55,000
Wrap-around (rear + side)	€2,500–€4,200	30 m² ≈ €78,000–€125,000
Two-storey, finished	€2,200–€3,200	40 m² (20 per floor) ≈ €90,000–€130,000

“Finished” means a habitable, decorated room — foundations, walls, roof, windows, insulation, electrics, plumbing, plastering and finishes. A higher spec (lots of glazing, premium kitchen, structural steel for open-plan) pushes you to the top of the range or beyond.

Cost by extension type

Single-storey rear — the most common extension, straight off the back of the house. Simplest to build and often within the 40 m² planning exemption, so it sits at the lower end per m².
Side return / infill — fills the narrow gap beside a kitchen on a terraced or semi-detached home. Small but pricey per m²: lots of foundations, roof and glazing relative to floor area, plus tight access.
Wrap-around — combines a rear and side extension into one L-shaped space. Larger footprint and more roof complexity, but a strong way to open up a kitchen-dining-living area.
Two-storey — adds rooms upstairs and down. Cheapest per m² because one foundation and one roof are shared across two floors, but it needs planning permission and more structural work.

Worked example: a kitchen extension

A 20 m² single-storey rear kitchen extension is the classic Irish project. At €2,500–€4,000 per m² the shell-to-finished build lands around €55,000–€90,000, before kitchen units and appliances. Add a mid-range fitted kitchen and the all-in figure typically reaches €70,000–€110,000+, depending on glazing (bifolds and rooflights add up fast) and finish level. For a city build, see our Dublin extension cost guide, where access and conservation push prices higher.

What’s included in the cost

Groundworks and foundations.
Structural shell — walls, steel beams, roof.
Windows, doors and glazing (rooflights and large sliders add cost).
Insulation to current Building Regulations.
Electrics, plumbing and heating extended into the new space.
Plastering, flooring and decoration.
Professional fees — see below.

Planning: the 40 m² exemption

Many single-storey rear extensions can be built without planning permission under the exempted-development rules, provided they stay within the limits in the regulations — including a 40 m² floor-area limit for the extension, conditions on how much can extend to the rear, height limits, and a requirement to retain a minimum of private open space behind the house. The exemption interacts with any previous extensions, so the 40 m² is effectively a cumulative cap.

First-floor extensions, front extensions and anything exceeding the limits will need a planning application. Always confirm your specific situation with the local authority or your architect before starting — getting this wrong is expensive to undo. For the full rules and the proposed 2026 changes, see our planning permission for extensions and garden rooms guide; if you do need to apply, our planning permission timeline and cost guide explains how long it takes and what it costs.

Even when planning is exempt, your extension must still comply with Building Regulations, and most extensions need a Commencement Notice and certification under Building Control — read Building Regulations and BCAR explained so you know what’s required before work starts.

Professional and extra fees

On top of the build cost, budget for:

Architect or architectural technician — design, drawings and tender.
Structural engineer — beam and foundation design.
Assigned certifier / Building Control compliance where required.
Planning application fee if not exempt.
Surveys (site, drainage) where needed.

These commonly add 10–15% to the overall project.

VAT, tax and financing

VAT. Building work in Ireland is charged at the reduced 13.5% VAT rate for construction services, not the 23% standard rate — make sure quotes state whether they’re VAT-inclusive so you’re comparing like for like.
No general extension grant. There’s no SEAI grant for the extension itself, and the old Home Renovation Incentive tax-relief scheme has closed. The energy-upgrade elements can still attract support, though — wrapping the existing house in insulation or installing a heat pump as part of the works may qualify (see the SEAI grants guide).
Financing. Most homeowners fund an extension from savings, a home-improvement loan, or by drawing down/topping up a mortgage; a mortgage top-up is usually the cheapest borrowing but needs lender approval and often a valuation.
Use a tax-compliant contractor and keep an itemised contract — it protects you on VAT, warranties and any future sale.

What affects the price

Size and number of storeys.
Glazing. Large sliders, bifolds and rooflights are costly.
Structural steel for open-plan layouts.
Ground conditions — poor soil or a high water table means deeper, pricier foundations.
Finish level — kitchen, bathroom, flooring and joinery spec.
Access — tight sites slow everything down.

The ideal time to upgrade your BER

An extension is the perfect moment to improve your home’s energy performance, because the disruption and scaffolding are already there. Consider wrapping the existing walls while you’re at it — see our external wall insulation cost guide — and read how to improve your BER rating for the upgrades that move the needle most. Improving insulation and airtightness during the build is far cheaper than retrofitting later.

Ways to save

Stay within the exemption where possible to avoid planning costs and delays.
Keep the shape simple — a rectangle is cheaper than complex angles and roof shapes.
Limit large glazing to where it earns its keep.
Get at least three written quotes on the same detailed drawings, so you’re comparing like for like.

Build in a contingency of 10–15%, and get a clear, itemised contract before work starts. If the extension is part of a wider project, our full house renovation cost guide helps you budget the whole job.

Frequently asked questions

How much does a house extension cost in Ireland in 2026?: As an indicative 2026 range, a finished single-storey extension costs roughly €2,500–€4,000 per square metre, so a 20 m² ground-floor extension works out around €55,000–€90,000. Two-storey extensions are typically €2,200–€3,200 per m². Planning, architect and engineer fees are extra. Always get at least three written quotes.
Do I need planning permission for an extension in Ireland?: Many single-storey rear extensions are exempt from planning permission if they stay within the limits set out in the planning regulations, including a floor-area limit of 40 m² for the extension (with conditions on how much can be to the rear and remaining private open space). First-floor and front extensions usually need permission. Always confirm with your local authority or an architect before building.
Is a two-storey extension cheaper per m² than single-storey?: Yes, usually. A two-storey extension shares one foundation and one roof across two floors, so the cost per square metre (around €2,200–€3,200 indicatively) is often lower than a single-storey extension (€2,500–€4,000 per m²). It does need planning permission and adds structural complexity.
What extra fees come with an extension?: Beyond the build cost, budget for architect or designer fees, structural engineer fees, an assigned certifier under Building Control regulations where required, planning application fees if not exempt, and connections or services. These professional fees commonly add 10–15% to the project.
How much does a kitchen extension cost in Ireland?: A 20 m² single-storey rear kitchen extension typically costs around €55,000–€90,000 for the finished build (indicative 2026 range), before kitchen units and appliances. With a mid-range fitted kitchen the all-in figure is usually €70,000–€110,000+, depending on glazing and finish. Always get at least three written quotes.
Why is a side return extension so expensive per square metre?: A side return or infill extension is small but has a lot of foundations, roof and glazing relative to its floor area, and it's usually built on a tight terraced site with difficult access. That pushes the cost per m² (around €2,800–€4,500 indicatively) above a simple rear extension, even though the total bill is lower because the floor area is small.
Is VAT charged on a house extension in Ireland?: Yes. Construction services in Ireland are charged at the reduced 13.5% VAT rate rather than the 23% standard rate. Check whether quotes are VAT-inclusive so you're comparing like for like, and use a tax-compliant contractor.