House Extension Cost Ireland 2026: What It Really Costs

What's Included in That Price?

A typical fixed-price quote for a standard rear extension covers:

• Foundations & structure — excavation, concrete strip foundations, block work walls, RSJ steel beams for openings
• Roof — a flat roof (felt over insulation board) typically costs €2,000–€4,000 less than a pitched roof; pitched is more durable over 20+ years
• Windows & doors — typically 1–2 windows and a rear door; bi-folds or sliding doors add €3,000–€8,000
• Internal plastering & insulation — dot and dab dry lining or wet plaster, floor insulation board
• Basic electrics and plumbing connections — first-fix wiring to sockets and lights, extending existing pipework
• Floor screed — ready for tiling, timber or whatever finish you choose

What's typically NOT included (common gotchas)

• Architect / technologist (planning drawings): typically €2,000–€4,500 excluding VAT for a standard domestic extension package — RIAI notes fees vary by scope; full architectural services through construction are often a percentage of build cost — get written quotes (+ VAT).
• Planning permission: €65 local authority application fee (plus consultant time above)
• Engineer's certificate of compliance — required for future sale; typically €500–€1,000
• Kitchen or bathroom fitting in the new space
• Landscaping and reinstatement of your garden after the build
• Decoration — painting, skirting boards, door furniture

Budget an extra €8,000–€15,000 on top of your build quote to cover these items for a typical project.

How Size Affects Cost

Smaller extensions cost more per square metre because mobilisation costs (scaffolding, site setup, plant hire) are spread across fewer metres. The sweet spot for cost efficiency is 20–40 sqm.

Planning permission threshold: A single-storey rear extension is exempt from planning permission up to 40 sqm. Side extensions are exempt up to 12 sqm. Combined with any previous extensions, the total must not exceed 40 sqm.

Location: Dublin vs The Rest of Ireland

Dublin contractors charge more due to higher day rates, material delivery costs, and strong demand. Here's how other cities compare to Dublin as a baseline:

Rural areas can go either way — lower contractor day rates but potentially higher material costs due to delivery, and fewer builders available to quote.

Budget vs Mid-Range vs Premium: What Changes?

Budget (multiply baseline by 0.70–0.75)

• Block-built walls — same structural spec
• PVC windows rather than aluminium
• Standard flat roof with felt membrane
• Basic plaster finish, no feature elements
• Standard electrics: sockets and pendant lights only

Mid-range (baseline)

• Aluminium or quality PVC windows with double glazing
• Underfloor heating as an option
• Insulated render or brick slip exterior finish
• Recessed lighting, additional sockets, CAT6 wiring

Premium (multiply baseline by 1.40–1.60)

• Architect-designed bespoke layout and detailing
• Bi-fold or sliding doors (€5,000–€12,000 for doors alone)
• High-spec insulation to near-Passive House standard
• Feature rooflights — fixed velux from €800, bespoke frameless from €4,000+
• Polished concrete or engineered timber floors

Do You Need Planning Permission?

Quick rule: A single-storey rear extension under 40 sqm is usually exempt from planning permission — but several conditions must all be met:

• The extension must not exceed 40 sqm combined with any previous extensions
• It must be to the rear of the house
• Height limits: 4m with a pitched roof, 3m with a flat roof
• The rear garden must not be reduced below 25 sqm
• No extension above ground floor level to the side of the house

For anything borderline, apply for a Section 5 Declaration from your local authority. It costs around €80 and gives you written confirmation of exemption — useful for future sale.

How to Get a Fair Quote

Three things to always do:

1. Get at least 3 quotes. A 20–40% spread between builders is completely normal. Don't assume the cheapest is the best or the most expensive is the highest quality.
2. Ask for a fixed-price contract, not a day-rate arrangement. Day-rate jobs frequently overrun; fixed-price contracts put the risk where it belongs.
3. Verify CIRI registration. Check your builder is on the Construction Industry Register Ireland (ciri.ie) before signing anything.

Red flags in quotes

• No itemised breakdown — you should see line items for foundations, structure, roof, windows, M&E, etc.
• Price per sqm below €1,200 — too cheap in almost all circumstances; corners will be cut somewhere
• “We'll sort the planning” with no architect named or involved — planning drawings require a qualified architect or engineer

Grants and Tax Relief

• Home Renovation Incentive (HRI): Tax relief on qualifying labour at 13.5% — check current eligibility at Revenue.ie, as the scheme has been updated.
• VAT: 13.5% applies to construction services. Quotes from VAT-registered builders should already include this — always confirm.
• SEAI grants: Only apply if the extension includes energy upgrades (insulation, heat pump integration, etc.). A standalone extension does not qualify on its own.

If you're combining an extension with a whole-house retrofit, you may be able to access SEAI's One Stop Shop scheme — worth checking before you finalise your scope.

Timeline: How Long Does It Take?

The timeline varies enormously depending on whether you need planning permission and how quickly you can find a builder.

Total from decision to move-in: 4–8 months with planning permission; 3–5 months for an exempt extension.

Real Numbers: What Irish Homeowners Actually Paid

Based on 150 extension costs gathered from Irish planning registers and homeowner forums (2023–2026):

• Median declared cost: €48,500
• P25 (cheaper quarter): €38,000
• P75 (more expensive quarter): €68,000
• Most common range: €45,000–€60,000 for a standard Dublin semi-D rear extension (25–35 sqm, mid-range spec)

These are declared costs from planning applications — they represent what homeowners told the council, which in some cases may be conservative. Forum-reported figures tend to run €5,000–€10,000 higher for comparable projects.

Final Checklist Before You Start