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House Extension in Dublin
Planning a rear, side or two-storey extension? This guide covers what an extension really costs in Dublin, when you need planning permission, who you need on the team and how long each stage takes.
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- 📍 Coverage Area: Dublin
- 💶 Typical Cost: €60,000–€140,000
- 🛠️ Response Type: Local vetted operators
- 🛡️ Standards: Certified & insured tradespeople
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- Typical cost: €60,000–€140,000
- Worked cost example for a 25m² extension
- Planning rules and exemptions explained
- Step-by-step process and timeline
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How an extension project works, step by step
Most extension problems, from budget overruns to disputes with builders, come from skipping the early steps. Getting the design, permissions and scope fixed before a builder starts is the single best way to protect your budget.
- Set your brief and budget. Decide what the space is for, roughly how big it needs to be, and the most you can spend. Keep 10–15% back as a contingency.
- Get a design. An architect or architectural technologist turns the brief into drawings. For a simple single-storey extension, design fees typically run 5–10% of the build cost.
- Check planning. Your designer confirms whether the extension is exempt or needs planning permission. A planning application usually takes 8–12 weeks to decide, longer if there is an appeal.
- Bring in an engineer. Foundations, steel beams and any opening into the existing house need a structural engineer's design.
- Prepare tender drawings and a specification. These describe exactly what is included: insulation, windows, heating, finishes. Without them, builders' quotes can't be compared fairly.
- Get at least three quotes. Compare them line by line, not just on the total.
- Sign a written contract. The RIAI or a similar standard form sets out price, programme, stage payments and how changes are handled.
- Build. Groundworks and foundations, walls, roof, windows, first-fix services, plastering, second fix, then finishes.
- Snag and sign off. Walk the job with your designer, list defects, and hold back a small retention until they're fixed. Get completion certificates for building regulations, electrics and any gas work.
What to check before you hire a builder
- Get quotes based on the same drawings and specification so they can be compared
- Check the builder is on the Construction Industry Register Ireland (CIRI)
- Ask for public and employers' liability insurance certificates
- Agree stage payments tied to work completed, never large upfront deposits
- Hold back a retention (often 2.5–5%) until snags are fixed
- Make sure your designer certifies compliance at the end
What an extension costs: a worked example
As a rough guide, a finished single-storey extension in Dublin costs around €2,500–€3,500 per square metre including 13.5% VAT, before the kitchen. Here is how a typical 25m² rear kitchen-dining extension on a semi-detached house might break down:
| Item | Typical cost |
|---|---|
| Build: foundations, walls, roof, insulation, plastering | €45,000–€60,000 |
| Glazing: sliding or folding doors and rooflights | €8,000–€20,000 |
| Opening into the house and steel beam | €4,000–€8,000 |
| Heating, electrics and plumbing | €6,000–€10,000 |
| Flooring and decoration | €3,000–€7,000 |
| Design, engineer and certification fees | €6,000–€12,000 |
| Total before kitchen | €72,000–€117,000 |
| New kitchen (optional) | €15,000–€40,000 |
What pushes the price up:
- Two storeys, or a complex roof such as a pitched roof with valleys
- Large areas of glazing or high-end aluminium doors
- Poor ground, nearby trees or drains under the extension footprint
- Restricted access, such as a mid-terrace house with no side entrance
- Underfloor heating or a heat pump
- Changes made after the build starts
These are indicative 2026 Dublin ranges. A quote based on your drawings is the only reliable figure.
Planning, building regulations and timelines
Planning permission and building regulations
Rear extensions can be exempt from planning permission if, among other conditions, the total floor area of extensions to the house stays within 40 square metres, enough private garden is left (at least 25 square metres), and height and boundary limits are met. Upstairs extensions have tighter size and distance limits. If the house has been extended before, that floor area counts towards the limit.
You will usually need planning permission for side extensions to the front building line, anything over the exempt limits, and work on protected structures or in architectural conservation areas. Your designer or the council's planning department can confirm.
Every extension must meet the Building Regulations, whether it needs planning or not. Larger projects also need a Commencement Notice and certification under the Building Control rules, so make sure your designer confirms what applies to you.
How long it takes
| Stage | Typical time |
|---|---|
| Design and engineer | 4–8 weeks |
| Planning permission (if needed) | 8–16 weeks |
| Tendering and choosing a builder | 3–6 weeks |
| Build on site | 12–16 weeks for single-storey |
Exempt projects can be on site within three months of starting the design. Projects that need planning usually take six to nine months from first drawings to a builder starting.
We cover house extension in every area below. Choose your district for local information.
| District | Areas covered |
|---|---|
| North Dublin City | Artane, Cabra, Clontarf, Coolock, Drumcondra, East Wall, Fairview, Glasnevin, Phibsborough, Stoneybatter |
| Dublin North Coast | Raheny, Baldoyle, Donaghmede, Howth, Sutton, Portmarnock, Malahide |
| North County Dublin | Swords, Lusk, Rush, Skerries |
| Dublin 15 | Blanchardstown, Castleknock, Mulhuddart, Ongar, Hansfield, Ashtown |
| West Dublin & Leixlip | Chapelizod, Palmerstown, Lucan, Leixlip, Adamstown, Clondalkin |
| South West Dublin | Tallaght, Citywest, Firhouse, Knocklyon, Ballyboden, Templeogue, Walkinstown, Kimmage, Rathfarnham, Terenure |
| South Dublin City | Ballsbridge, Donnybrook, Sandymount, Ranelagh, Rathgar, Harold's Cross, Churchtown, Dundrum |
| Dún Laoghaire & South Coast | Blackrock, Booterstown, Monkstown, Dún Laoghaire, Dalkey, Killiney |
| Stillorgan, Sandyford & Foxrock | Mount Merrion, Stillorgan, Goatstown, Sandyford, Cherrywood, Cabinteely, Foxrock, Deansgrange |
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Frequently Asked Questions
How much does a house extension cost in Dublin?
A finished single-storey extension typically costs €2,500–€3,500 per square metre including VAT. A 25m² rear extension usually comes to €72,000–€117,000 before a new kitchen.
Do I need planning permission for a rear extension?
Not always. Rear extensions within 40 square metres in total, leaving at least 25 square metres of garden and meeting height and boundary limits, can be exempt. Check with your designer or council.
Do I need an architect for an extension?
You need someone qualified to produce drawings and an engineer for the structure. An architect or architectural technologist can also handle planning, tendering and certifying compliance.
Can I live in the house during an extension?
Usually, yes, for most of it. The disruption peaks when the opening into the house is made and the kitchen is moved, so many families plan a short stay elsewhere then.
Does an extension add value to my house?
A well-designed extension that adds useful living space usually adds value, especially in areas where moving is expensive. It rarely adds back more than it cost if the finish is very high-end.
What is a contingency and how much should I keep?
Money set aside for unexpected issues, such as poor ground or hidden drains. Keep 10–15% of the build cost in reserve.
How Emergency Trade Works
Emergency Trade connects you with independent, vetted local tradespeople across Dublin and the rest of Dublin. Before any work starts, ask for a written quote and check the right registration for the job: RGII for gas work and Safe Electric for electrical work.