House Extensions in Dublin
A kitchen-diner out the back of a semi, a second storey over the garage, an attic turned into a fourth bedroom, or the full 45 square metres you can now build without a planning application. Tell us what you have in mind and we will pass it to an independent Dublin building contractor who does this work. It costs nothing, there is no obligation, and before anyone calls you we will tell you what decides the price and whether you need an architect first.
- Free, no-obligation quotes — you decide, and you can say no
- One enquiry, one call back — not five builders and five site visits
- Independent local builders — we introduce, they build, you deal with them direct
- Dublin, Kildare, Meath and north Wicklow — city, county and commuter belt
- Out of hours? You will hear back the next working day
Do You Need an Architect or a Builder First?
Half the people who search for house extensions in Dublin are looking for a builder and land on an architect's portfolio, or the other way round. Here is the honest sorting:
You Already Have Drawings
A builder can price them and you are ready to talk to one. Send us the drawings and the enquiry goes straight to a contractor.
You Have an Idea but No Drawings
A builder can give you a rough figure from a conversation, but not a price you can hold them to. You need an architect or an architectural technologist to draw it, and usually a structural engineer for the steel. We are not a design practice, but the contractor we pass you to will tell you what drawings they need and can point you to people who produce them. Our planning your extension guide explains who does what and in which order.
You Are Not Sure
Say so on the form. The "not sure, help me decide" option exists for exactly this, and a builder's first visit is often the cheapest way to find out whether your idea fits your house.
How House Extensions Dublin Works
House Extensions Dublin is an enquiry service, not a building company, and that deserves saying plainly.
You Tell Us the Job
Rear, side, two-storey, attic, garage, sunroom; roughly how big; whether you have drawings; when you would like to start. Call or use the form. It takes about a minute.
It Goes to an Independent Dublin Building Contractor
A builder who works in your part of the city or county gets your details and what you told us.
They Contact You and Quote
A site visit, a price against your drawings or a conversation about getting some. From there it is between you and them.
We do not do the building, we do not inspect the builder's work, and we do not claim to have checked anyone. Our part is to spare you the ring-round, and to hand you the questions that make a builder's quote make sense. Our planning your extension guide shows you how to check any builder yourself, including the one we introduce you to.
What Decides the Price of a Dublin Extension
There is no price list on this page. A figure off a website is almost never the figure you end up paying, so here is what actually moves an extension quote in Dublin:
- Square metres, less than you think. Foundations, the opening into the house, the drains and the roof edge cost the same whether the room is 20 m² or 40 m². Bigger is not proportionally dearer.
- One storey or two. Two storeys on one set of foundations is the best value per square metre and the biggest project in total.
- Opening up the back wall. The steel beam over the opening and the engineer who designs it are on nearly every kitchen extension.
- What is under the garden. A shared drain, an ESB cable, tree roots or made ground: none of it is on the sketch and all of it is on the invoice.
- Glass. Sliding doors across the back and a lantern above are the largest line after the shell.
- Finish level. Builder's finish, plastered and ready to decorate, is one number. Turnkey with floor, kitchen and lighting is another.
- Whether you have drawings. A price against drawings and a structural design is a price. A price from a chat is an estimate.
For researched 2026 Dublin ranges by extension type, with worked examples for a 20 m² and a 45 m² job and the costs quotes leave out, read our house extension cost guide.
Extension Services Across Dublin
Six kinds of work, one enquiry. Ordered by the size of the project.
Two-Storey Extensions
A room downstairs and a room upstairs on one set of foundations. Over the kitchen, to the side, or on a bungalow. Always through planning, always worth engineering properly.
Kitchen Extensions
Where most Dublin extension money goes: the steel across the back wall, the glass, and a floor full of services.
Single-Storey & Rear Extensions
The classic Dublin job. Rear, side, wrap-around or side return, and the one most likely to fit inside the planning exemption.
Sunroom Extensions
A glazed room built to the same standard as the house, used every day of the year, not a conservatory.
Attic Conversions
A bedroom without losing a metre of garden, and since July 2026 often without a planning application.
Garage Conversions
The cheapest room the house will ever gain, if it is insulated properly and the front wall matches.
The 40 m² Rule Is Now 45 m²
On 27 July 2026 the planning exemption for a rear house extension in Ireland went up from 40 to 45 square metres. Most of the internet, and most builders' websites, have not caught up. The 45 m² is a lifetime total for the house, so an earlier extension counts against it; the extension must be no higher than the house and must leave 25 m² of private open space behind it; and a two-storey extension is never exempt. One thing that did not change: the building-control threshold stayed at 40 m², so an extension between 41 and 45 m² skips planning but still needs a Commencement Notice. The whole picture, including the new dormer exemption for attics, is in our extension planning permission guide.
Extensions on Dublin Houses
The right extension depends on the house you have, and Dublin has a handful of house types that account for nearly everything.
The 1930s–1960s semi in Clontarf, Terenure, Rathfarnham, Dundrum and Stillorgan: a small back kitchen, a long garden, and a back wall that opens up easily. The classic rear kitchen extension, usually within the exemption.
The 1970s–1990s estate semi across Tallaght, Clondalkin, Lucan, Blanchardstown, Swords and Balbriggan: a kitchen and a separate dining room, an attached garage, a shorter garden. The 25 m² open-space rule is the one to check, and the garage is often the cheapest room to gain.
The Victorian and Edwardian terrace in Terenure, Dún Laoghaire and the older city: a side return to infill, a conservation-area check to make first, and a planning authority that takes character seriously.
The bungalow in Fingal and the Kildare and Meath commuter towns: room for a big single-storey extension, a low eaves line to work under, and a roof that may take a dormer under the new exemption.
The 1980s–2000s detached house in Castleknock, Malahide, Naas and Maynooth: the plot for a two-storey or wrap-around extension and a budget question that is mostly about finish.
Each of our area pages says which of these your street is likely to be and which planning authority you are dealing with.
Where We Cover
Enquiries from anywhere on this list go to a building contractor who works in that area.
Dublin city and north county: Clontarf · Donaghmede · Howth · Portmarnock · Malahide · Swords · Skerries · Balbriggan
West Dublin: Castleknock · Blanchardstown · Lucan · Clondalkin · Tallaght
South Dublin: Terenure · Rathfarnham · Dundrum · Stillorgan · Dún Laoghaire
Wicklow, Kildare and Meath: Bray · Greystones · Naas · Maynooth · Celbridge · Leixlip · Ashbourne · Dunboyne
Why Use House Extensions Dublin
It is free and there is no obligation. You get a quote from a builder. If you do not like it, that is the end of it.
One enquiry instead of five. You describe the job once. You do not spend a fortnight leaving voicemails for builders who are booked until spring.
A builder who actually does extensions. Not a handyman who will have a go, and not a national firm that sends a salesman.
We tell you what to ask. The price drivers above, the planning rules, and the checks to make on any builder, so the quote you get makes sense and the contract protects you.
Nobody from us visits your house. We are an introduction. The site visit is the builder's, and so is the relationship after it.
Frequently Asked Questions
How much does a house extension cost in Dublin?
It depends on the size, whether it is one storey or two, how much of the back wall comes out, what is under the garden, the glazing and the finish. We keep the figures in one place: our house extension cost guide has researched 2026 Dublin ranges and two worked examples.
How big an extension can I build without planning permission?
Since 27 July 2026, up to 45 square metres to the rear, as a lifetime total for the house, provided it is no higher than the house, leaves 25 m² of open space and meets the height and window rules. Two-storey extensions always need permission. Our extension planning permission guide has the detail.
Do I need an architect for an extension?
You need drawings, and for anything that opens up the back wall you need a structural engineer. Whether the drawings come from an architect or an architectural technologist depends on the job. Our planning your extension guide explains the choice.
Are you a building company?
No. We are an enquiry service that passes your details to an independent Dublin building contractor. We do not do the work and we do not inspect it; the builder quotes you direct and the contract is with them.
Get a Free Extension Quote in Dublin
Tell us what you want to build, roughly how big, and whether you have drawings. It goes to a Dublin building contractor who does this work, and they contact you. Free, no commitment, and it takes about a minute.