A house extension in Ireland is one of those projects that sounds simple at the start, then quickly becomes full of questions.
How big should it be?
Do you need planning permission?
Will the cost include the kitchen?
What about plastering, flooring, electrics, plumbing and finishes?
And the big one, how much will the whole thing actually cost?
Well, the honest answer is that house extension costs in Ireland can vary a lot. A small, simple rear extension will not cost the same as a two storey extension with structural steel, roof changes, plumbing, underfloor heating, large glazing and a high end kitchen. Location matters too. Access, ground conditions, finish level and the age of the existing house can all change the final price.
As a broad guide, many house extensions in Ireland now fall somewhere between €1,500 and €3,500 per square metre, depending on the type of extension, finish level and complexity. Some projects may come in below that range if the work is very straightforward, while more detailed or higher specification extensions can go above it.
That gives you a starting point, but it does not tell the full story. Let’s break it down properly.
Average House Extension Cost In Ireland
For a basic idea, you can estimate the cost by looking at the size of the extension first.
A 20 square metre extension might cost somewhere in the region of €40,000 to €70,000, depending on the build and finish.
A 30 square metre extension could cost around €60,000 to €100,000.
A 40 square metre extension may cost from €80,000 to €140,000 or more, especially if the finish is higher or the work is more complex.
A larger extension, or one with two storeys, structural alterations, expensive glazing, kitchen fitting or major plumbing work, can go well beyond this.
That is why it is risky to hear someone say, “extensions cost about this much,” without knowing what is actually included. One quote might include a builder’s finish only. Another might include plumbing, electrics, plastering, insulation, roof work, windows, doors, flooring, tiling and final finishes.
They are not the same price because they are not the same job.
What Does Cost Per Square Metre Mean?
Cost per square metre is a useful guide, but it is not perfect.
Think of it like pricing a car by size. A small car is usually cheaper than a large car, yes, but the model, engine, finish, age and features all matter. A house extension works the same way.
A simple rectangular extension with good access and a standard finish may stay closer to the lower end of the price range. A more detailed extension with rooflights, large sliding doors, steel beams, a new kitchen, bathroom work or major changes to the existing house will usually cost more.
The square metre rate gives you a rough starting point. It does not replace a proper site visit and quote.
What Affects The Cost Of A House Extension?
No two extension projects are exactly alike. Even if two homes are the same size, the cost can be very different because of what is involved behind the scenes.
Size Of The Extension
The bigger the extension, the higher the overall cost. That part is obvious. More space means more materials, more labour, more groundwork, more roofing, more plastering and more finishing.
That said, smaller extensions can sometimes have a higher cost per square metre because many fixed costs still apply. For example, a small extension still needs foundations, walls, roofing, insulation, windows, doors and site setup.
Type Of Extension
A single storey rear extension is usually more straightforward than a two storey extension.
A side extension may involve access challenges.
A wraparound extension can be more complex because it changes more of the existing structure.
An extension with a bathroom, utility room or kitchen will usually cost more than a plain living space because plumbing, drainage, electrics, tiling and fittings add to the budget.
Ground Conditions
The ground below the extension matters more than many homeowners realise. If the ground is soft, uneven, difficult to access or needs extra preparation, the foundation work may cost more.
Good groundwork is not the exciting part of an extension, but it is one of the most important parts. Like the roots of a tree, it supports everything above it.
Structural Work
Many extensions involve opening up the back or side of the house. This may require structural steel, temporary supports and careful work to connect the new extension with the existing building.
The more structural change involved, the more the cost can rise. This is especially true when creating open plan kitchen and living areas.
Finish Level
A basic finish and a premium finish are not the same price.
Flooring, tiles, windows, doors, lighting, kitchen units, worktops, bathroom fittings and paint choices all affect the final cost. Even small upgrades can add up quickly when they are repeated across a whole extension.
This is where homeowners often underestimate the budget. The shell of the extension is only part of the cost. The finish can be a major part too.
Access To The Property
If the builder can access the site easily, the job is usually more straightforward. If everything has to be carried through the house, down a narrow side path or around awkward garden access, the work can take longer.
Poor access can affect labour time, machinery use, deliveries, waste removal and site setup.
Age And Condition Of The Existing Home
Older homes can be lovely, but they can also hide surprises. Uneven walls, old wiring, poor previous work, damp areas, drainage issues or weak surfaces can all change the scope of the project.
Sometimes an extension reveals other work that should be dealt with at the same time. It is better to know this early rather than after finishes are installed.
What Is Usually Included In A House Extension Quote?
This depends on the builder and the level of finish agreed, so always ask clearly.
A house extension quote may include some or all of the following:
Foundations and groundworks
Blockwork or structural walls
Roofing
Insulation
Windows and doors
Internal plastering
Floor preparation
Electrical work
Plumbing and heating
Drainage work
Carpentry
Tiling
Painting
Kitchen or bathroom installation
Waste removal
Final finishes
Not every quote includes everything. Some quotes are for a builder’s finish, meaning the extension is structurally complete but may not include all final decoration, flooring, kitchen units or bathroom fittings.
Before comparing prices, make sure you are comparing the same level of work. A cheaper quote may not be cheaper at all if important items are missing.
Builder’s Finish Or Turnkey Finish?
This is one of the biggest things to understand.
Builder’s Finish
A builder’s finish usually means the main construction work is complete. The extension may be plastered, insulated, roofed and ready for further finishing, but items such as flooring, painting, kitchen fitting or certain final finishes may not be included.
This can suit homeowners who want to manage some of the finishing work themselves.
Turnkey Finish
A turnkey finish means the extension is completed to a ready to use standard. The builder or contractor manages more of the work, including final finishes, fittings and possibly decoration.
This usually costs more, but it can be easier for homeowners who want one clear process.
Neither option is wrong. You just need to know which one your quote is based on.
Do You Need Planning Permission For A House Extension In Ireland?
Some house extensions in Ireland may be exempt from planning permission if they meet certain conditions. For example, many rear extensions can be built without planning permission if they stay within size limits and follow the relevant rules.
However, planning rules can depend on the property, previous extensions, location, height, boundaries, protected structures and other factors. It is always worth checking before work begins.
Even if planning permission is not needed, building regulations still apply. The extension still needs to be safe, insulated, properly built and compliant.
A builder can advise from a practical point of view, but for planning certainty, homeowners may also speak with their local authority, architect or planning consultant.
Extra Costs To Keep In Mind
The building quote is only one part of the budget. Other costs may also apply depending on the project.
You may need drawings from an architect or technician. You may need an engineer if structural work is involved. You may need planning fees if permission is required. There may also be costs for kitchen units, bathroom fittings, flooring, painting, furniture, landscaping or temporary accommodation if the work is disruptive.
It is sensible to keep a contingency budget aside. Building projects can uncover surprises, especially in older homes. A contingency of around 10 percent to 15 percent is often wise, depending on the project.
Actually, this is one of the best ways to reduce stress. If every euro is already spent before the job begins, any unexpected issue becomes a major problem.
Is A House Extension Worth It?
For many homeowners, yes.
A well planned extension can give you more space, improve the layout and make the home much easier to live in. It can also help you avoid moving, which brings its own costs, stress and uncertainty.
An extension may be worth considering if you like your location but the house no longer works for your family. Maybe the kitchen is too small. Maybe you need a home office. Maybe the children need more space. Maybe the house feels dark, cramped or poorly laid out.
The key is to plan the extension around how you live, not just around adding square metres. A clever 25 square metre extension can sometimes feel more useful than a larger space that has not been planned properly.
How To Keep Extension Costs Under Control
The best way to control cost is to make clear decisions early.
Changing your mind halfway through a build can be expensive. Moving a wall, changing window sizes, altering plumbing or switching finishes after materials are ordered can all add time and cost.
Before starting, think carefully about:
The size of the extension
The layout
The finish level
Kitchen or bathroom choices
Windows and doors
Heating and lighting
Flooring
Storage
Access to the garden
How the new space connects to the existing home
Good planning saves money because it reduces confusion on site.
It also helps to be realistic. Trying to build a high specification extension on a low specification budget usually leads to disappointment. It is better to be clear about what matters most and spend money where it makes the biggest difference.
Questions To Ask Before Getting A Quote
Before asking for a quote, try to have a rough idea of what you want. You do not need every detail decided, but the clearer you are, the easier it is for a builder to price the work properly.
Useful questions include:
What size extension do I want?
What will the space be used for?
Do I want a basic finish or a complete finish?
Will the existing house need structural changes?
Is plumbing or drainage involved?
Will I need a new kitchen or bathroom?
Do I need drawings first?
Is access to the site easy?
Do I have a realistic budget?
A good builder will usually spot practical issues you may not have thought about.
Why A Site Visit Matters
Online cost guides are useful, but they cannot see your house.
A proper site visit allows the builder to look at access, ground conditions, existing walls, drainage, roof connection, layout and any obvious issues that may affect the work.
This is where a more accurate quote begins. Without seeing the property, any price is only a rough estimate.
A site visit also gives you a chance to ask questions, explain what you want and understand what may be involved before committing to the project.
Final Thoughts
So, how much does a house extension cost in Ireland?
For many homeowners, a rough guide is €1,500 to €3,500 per square metre, but the real answer depends on size, design, access, finish level, ground conditions, structural work and what is included in the quote.
A simple extension with a standard finish may be more affordable. A larger or more detailed extension with major internal changes, premium finishes and extra services will cost more.
The most important thing is not to focus only on the cheapest figure. A house extension is a major investment in your home. It needs to be planned properly, built safely and finished in a way that suits how you live.
If you are planning a house extension, start with a clear idea, get proper advice and make sure the quote explains exactly what is included.
FAQs
What Is The Cheapest Type Of House Extension In Ireland?
A simple single storey rear extension with a straightforward layout is usually one of the more affordable options. Costs rise when the design becomes more complex or includes major structural changes.
Is A Two Storey Extension More Expensive Than A Single Storey Extension?
Yes, a two storey extension usually costs more overall because it involves extra structure, walls, windows, flooring, roofing details and internal finishing. However, the cost per square metre can sometimes be better value than a small single storey extension.
Does A Kitchen Extension Cost More?
Usually, yes. A kitchen extension often includes plumbing, electrics, flooring, lighting, ventilation, cabinets, worktops and appliances, which can add a lot to the final price.
Should I Move Out During A House Extension?
It depends on the scale of the work. For smaller extensions, many homeowners stay in the house. For larger projects involving major structural work, kitchens or bathrooms, moving out temporarily may make life easier.
Can I Reduce The Cost By Doing Some Work Myself?
Possibly, but be careful. Painting, simple finishing or arranging certain fittings may be manageable for some homeowners. Structural work, plumbing, electrics and building work should be handled by qualified professionals.
How Long Does A House Extension Take?
A small extension may take a few months, while larger or more complex projects can take longer. Weather, access, design changes, materials and the condition of the existing property can all affect the timeline.
Do I Need An Architect For A House Extension?
Not always, but drawings are usually needed for proper planning, pricing and building. For more complex extensions, an architect, architectural technician or engineer can be very helpful.
Is It Better To Extend Or Move House?
That depends on your location, budget and long term plans. If you like your area and the house can be improved properly, extending may be a better option than moving.