Home Extensions Quotes in Ireland
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A home extension is one of the most significant investments you can make in your property, and in the current Irish housing market, it is often the smarter alternative to moving. The average cost of moving (stamp duty, legal fees, estate agent fees, moving costs) runs to €15,000 to €30,000 before you even consider the higher purchase price of a bigger home. An extension gives you the space you need at a fraction of the moving cost while adding real, measurable value to your existing property.
Extension costs in Ireland run from €2,000 to €3,500 per square metre for a standard single-storey rear extension, depending on specification and location. A typical 20 square metre kitchen-diner extension costs €40,000 to €70,000 all in. Two-storey extensions cost more overall but less per square metre (€1,800 to €3,000/m²) because the foundation and roof costs are shared across two floors. High-spec finishes, large-format glazing, or structural steel push costs to the upper end.
Many single-storey rear extensions up to 40 square metres are exempt from planning permission under exempted development rules, though conditions around height, boundary distances, and total site coverage apply. Extensions that require planning add 8 to 12 weeks to the timeline for the application process. An architect or engineer is essential for anything beyond a very basic extension, both for design quality and to ensure compliance with building regulations (Part L energy, Part B fire, Part M accessibility).
The difference between a smooth extension project and a stressful one nearly always comes down to the builder. A competent, well-organised builder who communicates clearly, sticks to timelines, and manages subcontractors effectively is worth more than a lower quote from someone unreliable. Comparing at least three detailed, itemised quotes from registered builders is the essential starting point.
How Much Does Home Extensions Cost in Ireland?
Typical pricing for home extensions services in Ireland (2026):
| Service | Typical Cost | Notes |
|---|---|---|
| Single-storey rear (20 sq m) | €40,000 | €70,000 | Finish level, ground conditions, access |
| Two-storey side (40 sq m) | €80,000 | €140,000 | Structure, foundations, services |
| Wraparound extension | €60,000 | €120,000 | Size, design complexity |
Extension costs vary most based on five factors: the size and shape of the extension, the structural complexity (steel beams for open-plan layouts cost €2,000 to €5,000 per beam), your specification level (standard vs premium finishes), whether you need a new kitchen or bathroom in the extension, and your location. Dublin builders charge 15-25% more than the national average. Rural areas may be slightly cheaper for labour but can carry material delivery surcharges. Always add a 10-15% contingency to your budget because extensions in older homes almost always uncover unexpected issues once walls and floors are opened up.
What to Expect: The Home Extensions Process
- Design and planning. Engage an architect or engineer to design the extension, produce drawings, and determine whether planning permission is needed or if the project qualifies as exempted development.
- Planning permission application (if required). Your architect submits the application to your local authority. The standard decision period is 8 weeks, with a possible extension to 12 weeks. Conditions may be attached.
- Building control notification. Your architect or engineer submits the Commencement Notice to the Building Control Authority (BCMS online portal). This must be done at least 14 days before work starts.
- Tendering. Your architect issues the drawings and specification to at least three builders for competitive quotes. Quotes should be itemised and include a provisional sum for unforeseen work.
- Construction. A typical single-storey rear extension takes 10 to 16 weeks from breaking ground to handover. Two-storey extensions take 14 to 22 weeks. Key phases are foundations, blockwork, roof, windows, first fix (electrics, plumbing), plastering, second fix, and finishes.
- Snagging and sign-off. Before final payment, walk through the extension with your architect and create a snagging list of any defects or incomplete work. The builder addresses these before you sign off.
Common Mistakes to Avoid
- Not getting detailed, itemised quotes. A lump-sum quote of '€60,000 for the extension' tells you nothing about what is included. You need a line-by-line breakdown so you can compare quotes on a like-for-like basis and identify what is excluded.
- Skipping the architect to save money. An extension built without proper design often results in poor light, awkward room proportions, and building regulation issues that cost far more to fix than the architect's fee would have been.
- Choosing the cheapest builder without checking references. The cheapest quote is often cheapest for a reason: cutting corners on materials, using unqualified subcontractors, or underestimating the job to win it and then hitting you with extras.
- Not budgeting beyond the build cost. Architect's fees, planning fees, building control, kitchen fit-out, landscaping, and making good the existing house all add up. The build is typically only 60-70% of the total project cost.
- Starting work before building control notification. Failure to submit a Commencement Notice is a legal requirement. Missing this creates problems when you sell because your solicitor cannot certify compliance.
What to Look for When Hiring a Home Extensions Professional
Your builder should be registered with the Construction Industry Register Ireland (CIRI), which is now a legal requirement for certain building works under the Building Control (Amendment) Regulations. Membership of the Construction Industry Federation (CIF) is an additional quality indicator. Homebond or Premier Guarantee registration means the builder is covered by a structural defects warranty scheme, which protects you for 10 years against major structural faults. Ensure your builder carries public liability insurance (minimum €6.5 million), employer's liability insurance, and contractor's all-risk insurance. Be cautious of builders who quote without visiting the site, who cannot provide references from similar recent projects, who ask for more than 10-15% deposit before work starts, or who refuse to work from architect's drawings.
Questions to Ask Your Home Extensions Professional
- Are you registered with CIRI? CIRI registration is a legal requirement for builders undertaking certain works. It confirms the builder meets minimum competency standards. Check the register at ciri.ie.
- Can you provide references from at least two recent extensions similar to mine? A builder who has completed similar work recently (same size, same type, same area) is more likely to deliver on time and within budget. Visit a completed project if possible.
- Is your quote fixed price or subject to variations? A fixed-price quote gives you certainty. If the quote includes provisional sums or allowances, understand what happens if the actual cost exceeds the allowance. Agree in writing how variations are handled.
- What is your realistic timeline from start to finish? Builders sometimes quote optimistic timelines to win the job. Press for a realistic week-by-week programme and ask what could cause delays (weather, material lead times, subcontractor availability).
- How do you manage subcontractors (plumber, electrician, tiler)? Most builders subcontract specialist work. The quality and reliability of these subcontractors directly affect your project. Ask who they use and whether the same teams are available for your project.
- What insurance and warranties do you carry? Public liability, employer's liability, and contractor's all-risk insurance are essential. A structural warranty (Homebond, Premier Guarantee) protects you against major defects for 10 years.
- What is your payment schedule? Standard practice is staged payments tied to milestones (foundations complete, walls up, roof on, etc.). Never pay more than the value of work completed. A large upfront deposit is a red flag.
Frequently Asked Questions
A standard single-storey rear extension costs €2,000 to €3,500 per square metre in Ireland. A 20 sq m kitchen extension therefore costs €40,000 to €70,000. A 40 sq m open-plan extension runs €80,000 to €140,000. Two-storey extensions cost €1,800 to €3,000 per square metre because foundation and roof costs are shared. These figures include the build but not architect's fees (8-12% of build cost), planning permission (€65 application fee), or kitchen/bathroom fit-out. Dublin prices are 15-25% above the national average.
Many single-storey rear extensions up to 40 sq m are exempt from planning permission under exempted development rules. However, exemptions come with strict conditions: the extension cannot exceed certain height limits, must not reduce the rear garden below 25 sq m, and the total floor area of all extensions cannot exceed the original house's floor area by more than a set amount. Two-storey extensions generally require planning permission. If your home is a protected structure or in an Architectural Conservation Area, different rules apply. Always verify with your architect or local authority before assuming exemption.
A straightforward single-storey rear extension typically takes 10 to 16 weeks from breaking ground to handover. A two-storey extension takes 14 to 22 weeks. If planning permission is required, add 8 to 12 weeks for the application process. Design and tendering take another 4 to 8 weeks before work starts. In total, expect 6 to 9 months from first meeting your architect to moving into the finished extension. Weather delays (particularly in winter), material supply issues, and subcontractor scheduling can all extend the timeline.
Legally, you do not need an architect for small exempt extensions, but it is strongly advisable for anything beyond a very basic box. An architect ensures your extension is well-designed (maximising light, space, and flow), compliant with building regulations, and properly documented for building control. They also manage the tender process, inspect the work during construction, and handle snagging. Architect's fees are typically 8 to 12% of the build cost, and for most homeowners the investment pays for itself in a better result and fewer problems.
Open-plan kitchen-living-dining extensions add the most value because they create the type of living space that Irish buyers now expect. Large glazed openings onto the garden (sliding or bi-fold doors) are highly desirable. Underfloor heating in the new space is a relatively low-cost add that buyers value. A well-designed utility room and good storage are also consistently cited by estate agents as value-adding features. Poorly designed extensions that create awkward layouts or block light from existing rooms can actually reduce value.
Under Irish building regulations, you must submit a Commencement Notice to the Building Control Authority via the BCMS online system at least 14 days before work starts. For extensions over 40 sq m, this is a Statutory Commencement Notice, which requires an assigned certifier (architect or engineer) and supporting documentation. For smaller extensions, an optional Commencement Notice may be used. Your architect or engineer handles this paperwork. Non-compliance with building control can create serious problems when you come to sell.
Absolutely. Every experienced builder and architect will tell you to add 10 to 15% contingency to your extension budget. Extensions in older homes almost always uncover surprises: poor foundations, hidden drainage, asbestos in old materials, structural issues in party walls, or services (gas, water, electric) in unexpected locations. Without a contingency, unexpected costs cause stress and compromise the finish quality as you cut corners to stay within budget.
In most cases yes, though it involves disruption. Expect noise during working hours (typically 8am to 5pm, Monday to Friday), dust despite protective sheeting, temporary loss of access to parts of your home, and possible disruption to water, heating, and electricity during connection phases. If the extension involves your kitchen, plan for several weeks without cooking facilities. Some homeowners with young children or health concerns choose to stay elsewhere during the most disruptive phase (foundations and structural work, typically 3 to 4 weeks).
A new extension must meet current building regulation standards for insulation, which are far higher than older parts of the house. This means the extension itself will be very energy-efficient. However, if the rest of your home is poorly insulated, the overall BER may not improve dramatically because the assessment covers the whole house. For the best BER outcome, combine the extension with upgrades to the existing house (attic insulation, heating controls, LED lighting). Get a BER assessment after completion to document the improvement.
Home Extensions Quotes by County
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