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Compare registered, insured home extension contractors. Get transparent 2026 cost benchmarks, planning exemption guidance, and competitive tenders for single and double-storey additions.
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Explore dedicated local extension guides, planning exemption rules, and vetted builders across affluent South Dublin suburbs:
A thoughtfully engineered house extension is the most effective way to unlock extra square footage, create modern open-plan living, and connect your home seamlessly with your garden. Whether you are building a contemporary rear kitchen extension with flat roof glazing or adding a two-storey side return, navigating building regulations and selecting the right builder is critical.
At Constructors.ie, we connect homeowners directly with verified general builders and extension specialists who are CIRI registered, fully insured, and vetted for quality workmanship across Ireland.
Seamless open-plan kitchen/dining spaces featuring flush floor-to-patio thresholds, expansive sliding doors, and frameless roof lights.
Engineered with high-density subfloor PIR insulation, thermally broken aluminium glazing, and airtightness membranes complying with TGD Part L.
Maximise up to 40 square metres of ground-floor floor space under standard Irish exempted development legislation without planning delays.
Realistic cost benchmarks based on tender data across Dublin and Leinster:
| Extension Type | Cost / m² (Gross) | Typical Size | Estimated Total | Duration | Scope of Inclusions |
|---|---|---|---|---|---|
| Single-Storey Rear Extension (Standard Build) | €2,000 – €2,600 / m² | 30 m² – 40 m² | €65,000 – €100,000 | 10 – 14 weeks | Cavity blockwork or timber frame, flat roof with EPDM or single-ply membrane, standard aluminium sliding doors, standard rooflight, basic electrical and radiator connections. |
| Architect-Designed Open-Plan Kitchen Extension | €2,600 – €3,500 / m² | 35 m² – 50 m² | €95,000 – €175,000 | 12 – 18 weeks | Structural knock-through with substantial RSJ steel framing, floor-to-ceiling slimline aluminium bifolds/sliders, frameless glass roof lanterns, underfloor heating, and bespoke island kitchen. |
| Two-Storey Side & Rear Extension | €2,200 – €3,000 / m² | 60 m² – 90 m² | €140,000 – €260,000 | 16 – 24 weeks | Ground floor kitchen/dining expansion plus first-floor master bedroom suite with ensuite bathroom. Requires full planning permission and structural foundation underpinning. |
| Over-Garage First-Floor Extension | €2,200 – €2,800 / m² | 20 m² – 35 m² | €50,000 – €95,000 | 10 – 14 weeks | Building above an existing attached garage. Requires structural foundation verification, new steel lintels, full roof restructuring, and complete internal bedroom/bathroom fitout. |
* Costs exclude 13.5% VAT on building services, kitchen cabinetry supply, and professional architectural/engineering fees (typically 8–12%).
Key requirements for building without full planning permission under Class 1 of the Planning Regulations:
Under Irish Planning Law (Planning and Development Regulations), single-storey rear extensions up to 40 sq. metres (430 sq ft) are generally exempt from planning permission for detached and semi-detached houses.
You must retain a minimum of 25 square metres of usable private open rear garden space after the extension is constructed.
The roof height of a single-storey flat roof extension must not exceed 4 metres (or 3 metres if adjacent to a shared boundary). Pitched roofs must not exceed the ridgeline of the existing house.
For peace of mind (and mortgage / future sale conveyancing), obtain a Section 5 Declaration of Exemption from your local authority (e.g. DLR CoCo, DCC) before commencing works.
From architectural drawings to final completion certificates:
Define your spatial requirements, lifestyle flow (kitchen island, utility room, boot room), and natural light orientation. Prepare dimensioned plans.
A structural engineer calculates RSJ steel sizes for load-bearing knock-throughs, designs pad footings, and assesses drainage and soakaway locations.
Issue comprehensive drawings and specifications to 3 vetted CIRI-registered building contractors for fixed-price transparent itemised pricing.
Excavation, concrete pour, radon barrier, blockwork / timber frame erection, roof joists, weather-tight roofing membranes, and glazing installation.
First/second fix plumbing, electrics (RECI), underfloor heating screed, plastering, kitchen and joinery installation, snagging, and Certification of Compliance.
Compare registered builders serving your area or request matching quotes below.
Your walls are leaking heat. We wrap them.
Unit 20, Westlink Industrial Estate, Kylemore Road, Inchicore, Dublin 10, D10 TD35
Isotherm is a direct Dublin EWI and ICF contractor based in Unit 20 Inchicore. Installing NSAI-certified Baumit external wall insulation and structural ICF builds across Dublin, Kildare, and Leinster.
High-Quality Home Renovations & House Extensions in Dublin & Leinster
Glenageary, Co. Dublin, Ireland
Based in Glenageary, Co. Dublin, Structure Build specializes in residential home renovations, house extensions, and bespoke carpentry across Dublin and the Leinster area.
A standard single-storey house extension in Ireland currently ranges from €2,000 to €2,600 per square metre. Architectural bespoke extensions with large structural knock-throughs, floor-to-ceiling glass sliders, and frameless roof lanterns cost between €2,600 and €3,500+ per square metre. A typical 35 sq. m. rear kitchen extension averages €85,000 to €125,000 depending on kitchen and glazing specifications.
Under the Planning and Development Regulations, ground-floor extensions to the rear of your home up to 40 square metres (430 sq ft) are exempt from planning permission, provided you retain at least 25 sq. metres of private rear garden, do not exceed the existing roof height, and keep the structure behind the front building line. Note that any previous extensions count towards the 40 sq. m. cumulative limit.
A standard 30 to 40 sq. m. single-storey rear extension typically takes 10 to 16 weeks of on-site construction. Two-storey extensions require 16 to 24 weeks. Pre-construction architectural design, engineering calculations, and tendering usually take an additional 6 to 10 weeks.
Traditional concrete block extensions offer exceptional acoustic density, robust masonry feel, and thermal mass. Timber frame extensions (or light gauge steel) are factory-manufactured, allowing ultra-fast on-site weather-tight erection (often within days) and exceptional airtightness. Both can achieve an A-rated thermal envelope when properly insulated.
Flat roof extensions with parapet boundary walls require high-grade waterproof membranes (such as single-ply or torch-on felt) capped with precision fabricated polyester powder-coated (PPC) aluminium parapet cappings. Quality fabricators (such as cills.ie) provide continuous drip edges to prevent rainwater tracking down rendered exterior walls.
Always use a standard RIAI (Royal Institute of the Architects of Ireland) Blue or Yellow form building contract. Payments should strictly be tied to agreed completion milestones (e.g. Substructure complete, Roof watertight, Plastered, Second fix, Practical Completion) with a 5% to 10% retention withheld until all snag list items are resolved.