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cost of a house extension uk: Ultimate UK costs guide
- Dan Hall
- 1 day ago
- 15 min read
Figuring out the cost of a house extension in the UK can feel like a guessing game, but it doesn't have to be. As a starting point, our in-house experts recommend you budget somewhere between £2,200 and £3,300 per square metre (excluding VAT).
For a typical single-storey extension, that translates into a total project cost of roughly £60,000 to £140,000, though this can swing quite a bit depending on the final size and the spec you go for. Our team can provide a detailed quote to give you a clearer picture.
Your Quick Guide to a Highcliffe House Extension
Embarking on a home extension, whether you're in coastal Highcliffe or bustling Southampton, is an exciting prospect. But before you get lost in paint swatches and bi-fold door catalogues, getting a firm grip on the finances is the first, most critical step.
The final price tag is a mosaic of different factors. Everything from the sheer size and complexity of the build to the quality of the kitchen units and bathroom tiles you choose will play a part.
To get a realistic baseline, it helps to understand the costs by the build route you take. In the UK, the average single-storey extension costs between £2,200 and £3,300 per square metre (ex. VAT).
If you're brave enough to manage the project yourself and hire individual trades, you might land at the lower end of that scale, around £2,200 to £2,700 per square metre. However, most people opt to hire a main contractor who manages everything and provides a single point of contact. Our in-house services provide this peace of mind, with costs typically between £2,700 and £3,300 per square metre, but it buys you professional oversight and a whole lot of peace of mind.
Self-Managed vs Contractor Costs in Bournemouth
This infographic gives a great visual on the cost difference between going it alone versus hiring a full-service contractor for your extension in Bournemouth.
As you can see, while a self-managed project might look cheaper on paper, using an experienced contractor with in-house services is invaluable for keeping complex projects in areas like Bournemouth and Poole on track and on budget.
A key takeaway is that your budget should not only cover the build itself but also account for professional fees, planning applications, and a contingency fund of at least 10-15% for any unforeseen issues.
To give you an even clearer picture, here’s a look at how the numbers stack up for the most common types of extensions across the UK.
Average UK House Extension Costs at a Glance
This table provides a quick summary of typical costs per square metre and the total project investment you can expect for different extension styles.
Extension Type | Average Cost per m² (ex. VAT) | Typical Total Project Cost (ex. VAT) |
|---|---|---|
Single-Storey Rear | £2,200 - £3,300 | £60,000 - £140,000 |
Two-Storey | £2,240 - £3,840 | £108,000 - £180,000 |
Wrap-Around | £2,400 - £3,600 | £85,000 - £160,000+ |
This data gives you a solid foundation for planning your budget and understanding what’s achievable.
Choosing the right team is absolutely essential to making sure your project in Christchurch or Ringwood stays on budget and delivers the quality you expect. At Hallmoore Developments, our in-house services and transparent pricing ensure you are always informed and in control.
For more guidance on selecting the best professionals for your job, check out our guide on finding trusted builders in Hampshire.
How Your Choice of Extension Shapes the Final Bill
Not all extensions are created equal, and neither are their price tags. Understanding the typical cost of a house extension in the UK is the first step, but the specific type you choose will have the biggest impact on your budget.
From a straightforward single-storey rear extension to a more complex wrap-around or two-storey build, each design comes with its own set of structural, material, and labour costs.
Think of it like building with Lego. A simple, single-level structure is one thing. But adding extra floors or wrapping around existing corners requires a much stronger, more carefully planned foundation. Every layer of complexity adds to the final cost.
A single-storey rear extension is often the go-to for families in Christchurch looking for that bit of extra living space. These projects typically fall between £2,200 and £3,300 per square metre (excluding VAT), with the final figure depending on the level of finish and how easy it is to access the site.
Single-Storey Rear Extensions in Christchurch
For a basic rear extension, your main costs are the foundations, structural walls, roofing, and standard finishes. For instance, a reinforced concrete slab might cost £70–£90 per m², while the external brickwork could be around £120–£150 per m².
Foundations: Reinforced concrete footings to give you stable ground support.
Walls and Structure: Insulated brick or blockwork to meet current building regulations.
Roof: A pitched or flat roof system, fully insulated and waterproofed.
Finishes: The windows, doors, flooring, and decorating that bring the space to life.
It's the most predictable type of build, keeping the financial surprises to a minimum. Our in-house services can manage all these elements for a seamless build.
Side-Return and Wrap-Around Extensions in Poole
A side-return extension cleverly utilises that often-neglected alleyway space next to your kitchen, adding width without eating into your garden. You should budget for £2,400 to £3,600 per m² for this, as working in a tighter space and tying into existing walls requires more labour and structural support.
Wrap-around extensions are the best of both worlds, combining a side-return with a rear extension to create a stunning open-plan L-shaped space, perfect for homes in Highcliffe or Ringwood. Here, you’re looking at total project costs of anywhere from £85,000 to £160,000, heavily dependent on the final size and specification.
Extension Style | Cost per m² (ex. VAT) | Typical Total Cost |
|---|---|---|
Single-Storey Rear | £2,200 – £3,300 | £60,000 – £140,000 |
Side-Return | £2,400 – £3,600 | £65,000 – £150,000 |
Wrap-Around | £2,400 – £3,600 | £85,000 – £160,000+ |
Case Study in Ringwood
Sarah, a client of ours in Ringwood, wanted the ultimate kitchen-diner. She opted to combine a 20m² side-return with a 10m² rear infill to create a seamless open space. Her project came to a total of £78,000, which also included VAT and some landscaping work.
Early collaboration: The Hallmoore team planned all the mechanical and electrical elements from day one using our in-house services, which avoided costly changes down the line.
Bulk buying: We ordered all materials in one go, saving her around 8% on supply costs.
Two-Storey Extensions in Bournemouth
Adding a second floor is a fantastic way to gain maximum space, but it comes with a significant jump in cost. A double-storey extension will typically add 50–60% to the price of its single-storey equivalent.
This isn't just about more bricks; it's about more complexity.
Additional engineering: More steel beams and detailed calculations are needed to support the upper floor.
Foundation upgrades: Groundworks must be deeper and stronger to handle the extra weight.
Building regulations: Stricter safety standards mean higher fees and more inspections.
For a standard 60-square-metre double-storey extension, homeowners should set aside a budget between £108,000 and £180,000, with a realistic average cost hovering around £144,000. On top of this, professional fees for architects (£4,500 to £6,500), structural engineers (£1,500 to £2,500), and building regulations compliance (£1,200) will add roughly another 10% to the total project cost.
A two-storey build isn't simply double the cost of a single-storey one; the price reflects the added structural complexity, engineering, and safety requirements involved.
Hallmoore’s Support at Every Stage
No matter which route you choose—rear, side-return, wrap-around, or two-storey—Hallmoore Developments has the in-house expertise to manage it all.
Design services: Our architects and structural engineers work together to streamline the planning process.
Gas Safe services: Our certified engineers handle all gas and electrical installations safely and professionally.
Project management: You get a single point of contact to keep your extension on schedule and on budget.
In-house trades: From plastering and plumbing to decorating and landscaping, it’s all handled under one roof.
If your project involves a new kitchen, you’ll find our guide on the UK average cost of kitchen extension complete pricing guide really helpful.
Choosing the right type of extension and the right building partner is crucial for protecting your budget. In the next section, we’ll break down the other key factors that can influence your final bill.
Key Factors That Influence Your Final Bill
Homeowners often budget by square metres and still end up surprised. Whether you’re in Highcliffe or Ringwood, where you build can nudge labour rates and material prices up or down. Scaffolding in Poole, for instance, usually comes at a higher fee than in rural Hampshire.
Spotting these cost drivers early is like laying out ingredients before you cook—you sidestep nasty surprises. Hallmoore’s Gas Safe registered team in Southampton tackles all M&E requirements in-house, keeping costs in check. From Christchurch design tweaks that saved thousands to clever Bournemouth tweaks, real-world examples prove the difference.
Below, we break down structural work, finishes, site access, ground conditions and M&E scope so you can plug budget leaks before they happen.
Structural Complexity In Ringwood Builds
Structural work often represents the single biggest upfront cost in Ringwood. Removing or shifting a load-bearing wall demands steel beams, support columns and precise engineer calculations.
This can tack on £3,000 to £8,000 to your final bill, depending on span and specification. Think of it like swapping a flimsy bookcase for a solid oak cabinet—the stronger option takes more resources.
Hallmoore’s in-house engineers liaise directly with structural consultants to ensure every beam, bolt and permit is covered. Finalise structural plans before work begins to avoid pricey change orders.
Typical structural tasks include:
Steel Beam Installation – £4,000 to £7,000 (labour and fabrication)
Temporary Propping – £500 to £1,200 (short-term support and removal)
Engineer Fees – £1,000 to £2,500 (design, site visits, calculations)
Finish Choices In Poole Extensions
Finishes alone can swing your budget by tens of thousands. Standard laminate flooring sits at £20 per m², while premium oak can exceed £100 per m².
Doors, walls and fixtures follow the same pattern—budget doors at £100, bespoke designs at £1,000+. The kitchen fit-out is a heavyweight cost, too; explore affordable kitchen cabinet upgrades to stretch your budget further.
Choosing mid-range over high-end finishes can alter your final bill by 15–25%.
Hallmoore Developments leverages bulk buying in Poole to pass on material discounts. A premium paint coat might only add £3 per m², but those pence soon become pounds.
Site Access And Ground Conditions In Bournemouth And Christchurch
Site access and ground conditions often slip under the radar. Narrow alleys in Bournemouth usually need skip permits and manual muck removal, costing £1,000 to £2,500. Meanwhile, clay-rich soils in Christchurch often call for piled foundations.
Poor drainage or high water tables can force in specialist sump systems at an extra £2,000 to £5,000. Tackling these issues up front prevents expensive on-the-spot changes once your digger’s in.
Cost Influencers Breakdown
Before you finalise your quote, consider how groundworks and logistics affect the bottom line. The table below offers a snapshot of typical factors and their budget impacts.
Cost Influencers Breakdown
Cost Factor | Potential Impact On Budget | Example |
|---|---|---|
Skip Permits | £200 – £500 per permit | Required for narrow alleys in Bournemouth |
Muck Removal | £50 – £80 per m³ | Manual excavation in tight spaces |
Piled Foundations | £150 – £300 per m² | Clay-rich soil in Christchurch |
Drainage Systems | £2,000 – £5,000 | High water table installations |
These figures underline how varied site conditions can reshape your groundwork outlay.
Mechanical And Electrical In Southampton Projects
M&E often surprises UK homeowners. A full first fix for a 30m² extension typically sits between £5,000 and £8,000, covering wiring, plumbing and gas work. Hallmoore’s in-house Gas Safe engineers handle every installation with no hidden mark-ups.
Complex systems such as underfloor heating add £80 to £120 per m² but deliver efficient warmth and strong ROI. Keeping services under one roof trims coordination fees and avoids schedule clashes.
For compliance details, see our guide on UK building regulations in Building Regulations Explained.
By planning around these key factors, you can forecast the cost of a house extension uk far more accurately. Early collaboration with Hallmoore Developments in Highcliffe, Bournemouth and Southampton brings clarity to every invoice line.
Our transparent quotes list each element—structural work, finishes, groundwork and M&E—so you know exactly where your money goes. With a sensible 10–15% contingency, you’ll protect your project against unexpected overruns.
Next, we’ll unravel hidden fees and professional charges to help you plan with confidence.
Getting to Grips with Hidden Costs and Professional Fees
Any extension that finishes on budget is a success story. But getting there means looking past the headline builder's quote and understanding the full picture. The true cost of a house extension in the UK is a mix of the build itself, a raft of professional fees, and a few potential expenses that can catch homeowners by surprise. Think of this section as your financial map, flagging up every cost so you can plan your journey with confidence.
From planning applications to structural engineering reports, these initial outlays aren't optional extras—they're essential investments. They form the bedrock of a safe, legal, and brilliantly executed project. Here at Hallmoore Developments, our in-house services make it our business to walk homeowners in Highcliffe and Bournemouth through these costs right from the start, ensuring our quotes are transparent and comprehensive, leaving no room for nasty surprises down the line.
Your Non-Negotiable Contingency Fund
Before we get into the itemised list, let's talk about the single most important part of your budget: the contingency fund. This is your financial safety net, typically 10-15% of your total project cost, set aside purely for the unexpected.
No matter how perfectly a project is planned, surprises can happen. Your builders might hit poor ground conditions that demand deeper foundations, or an ancient drainpipe decides to make a sudden appearance right where your new wall should be. Without a contingency pot, these hiccups can either halt your project or force you to cut corners on the finishes you’ve been dreaming of. It's basically project insurance—you hope you never need it, but you'll be incredibly glad it's there if you do.
Unpacking the Professional and Council Fees
Long before the first brick is laid, a team of professionals and council departments need to be involved. Their fees ensure your new extension is structurally sound, fully legal, and meets all UK building standards.
Here are the main fees you'll need to budget for:
Architect and Design Fees: Expect this to be somewhere between £2,000 and £6,000. This covers the detailed drawings that bring your vision to life and are crucial for navigating the planning system.
Structural Engineer Reports: If you’re knocking through walls or adding a new structure, a structural engineer is non-negotiable. They make sure everything is safe and sound, with reports and calculations typically costing £1,000 to £2,500.
Planning Application Fees: The standard fee for submitting a planning application to your local council in England is currently £206. If you want to get a better handle on the whole process, our guide on UK home extension planning permission explained is a great place to start.
Building Regulations Approval: This is a separate step from planning permission. It's all about making sure your extension meets health and safety standards. The fees vary depending on the project size but usually fall between £500 and £1,200.
Party Wall Agreements: Building on or near a boundary with a neighbour? You'll likely need a Party Wall Agreement. This can cost anywhere from £700 to £1,500 per neighbour, especially if surveyors for both sides get involved.
Other Costs That Can Hide in Plain Sight
It’s easy to forget about the practical costs that pop up during the build. For instance, you'll probably need to clear out a room or two, so remember to factor in the cost of furniture storage. Other things people often overlook include setting up a temporary kitchen, re-landscaping the garden once the diggers have gone, or even buying new furniture to fill your beautiful new space.
It's not uncommon for hidden extras like temporary kitchen setups, garden restoration, and storage to add another £3,000 to £5,000 to the total project cost.
Building these items into your budget from day one is the secret to avoiding financial headaches later on. It's also worth remembering that where you live matters. Building costs in London, for example, are roughly 9% higher than in other parts of the country.
By working with a transparent partner like Hallmoore Developments, homeowners in Christchurch and Poole can confidently navigate every single fee, ensuring a smooth and predictable financial journey from start to finish.
So, you’re ready to take the plunge and plan that dream extension? Getting a handle on the total cost of a house extension in the UK is about more than just the builder's final number. Let's walk through a practical, step-by-step roadmap that takes you from the initial spark of an idea right through to the final handover.
Think of this as your project bible. It’s designed to help you figure out exactly what you need, set a budget that won’t give you sleepless nights, and confidently navigate the planning process in areas like Poole. Following these steps will put you in the best position to choose a brilliant, reputable contractor for your project, whether you're in Christchurch or the surrounding areas.
Step 1: Define Your Needs and Set a Realistic Budget
Before a single sketch is drawn, you need to get crystal clear on two things: why you want an extension and what you can genuinely afford to spend. Are you dreaming of a sprawling kitchen-diner for your family in Bournemouth, or is it a quiet, dedicated home office you need in Ringwood?
Your 'why' is the anchor for the entire project. The more specific you are about your goals and how you'll use the new space, the smoother everything will go.
Once that’s locked in, it’s time to talk numbers. Use the average costs we’ve discussed as a ballpark figure, remember to account for professional fees, and—this is crucial—always build in a contingency fund of 10-20% of the total build cost. Trust me, it’s the buffer that will save you a lot of stress down the line. Our team can help you formulate a realistic budget.
Step 2: Get Initial Designs and Cost Estimates
With a clear vision and a working budget, you can start exploring some initial design ideas. You don’t need a full-blown architectural plan just yet. A good design-and-build company like Hallmoore Developments can sit down with you and create concept sketches that bring your vision to life using our in-house design services.
This is the stage where the numbers start to become real. It’s always smart to approach at least three reputable local builders. Give each of them the exact same detailed brief—that way, you’re comparing apples with apples when their quotes come back.
A proper, detailed quote isn't just a single figure on a piece of paper. It should clearly break down the costs for materials, labour, structural elements, and finishes. That transparency is your window into where every penny is going.
Step 3: Navigate Planning and Regulations
Once you’ve settled on a design you love, the next hurdle is the official paperwork. Your project might need planning permission from the local council, depending on its size and location—whether that’s in Poole, Christchurch, or Southampton.
Even if your build falls under Permitted Development rights (meaning no full planning application is needed), you will absolutely still need Building Regulations approval. This isn't optional; it ensures all the work is structurally sound, safe, and meets today's energy efficiency standards. A good contractor will handle this entire process for you, submitting drawings and liaising with council inspectors on your behalf. Our in-house services cover all of this.
For a much deeper dive into this, check out our complete guide on how to plan a house extension in Hampshire, which covers costs, permits, and everything in between.
Step 4: Select Your Contractor and Finalise the Details
Choosing the right contractor is probably the single most important decision you will make. Please, don’t just opt for the cheapest quote. Look for a team with a solid track record, fantastic local reviews, and comprehensive insurance.
Before you sign any contract, make sure you ask these key questions:
Can I see examples of your previous work in Highcliffe or Bournemouth? Any builder worth their salt will be proud to show off their portfolio and connect you with past clients.
What is the payment schedule? Payments should always be tied to specific project milestones being completed, not demanded in large chunks upfront.
Who will be my main point of contact? Consistent, clear communication is the secret sauce for a stress-free build.
What, exactly, is included in your quote? Make sure everything from skip hire to that final lick of paint is itemised. This is how you avoid nasty hidden costs later.
At Hallmoore Developments, we’re here to manage this entire journey for you. From those first rough sketches to the final handover, our in-house team of experts provides a seamless, stress-free experience, focused on delivering your perfect home extension on time and on budget.
Your House Extension Questions Answered
Home extensions spark plenty of questions. In this final section, we tackle the ones we hear most often. Our aim is to give you clear, honest answers so you can go forward with confidence.
How Much Value Does An Extension Add To A UK House?
An extension’s lift to your property value hinges on its location, build standard and the type of space you create. Get it right and you could see a boost of 10–20% when you come to sell.
Kitchen Extensions and Loft Conversions tend to offer the strongest returns.
Avoid over-capitalising—if your home becomes the priciest on the street, you might not recoup the full cost.
For example, a well-executed loft conversion can add up to 20%, while a double-storey extension often delivers around 12%.
At Hallmoore Developments, our in-house services help Bournemouth and Poole homeowners with projects that balance design flair with sound financial sense.
Do I Always Need Planning Permission For An Extension In Christchurch?
Not always. Many smaller builds fall under Permitted Development rights, so you can skip a full planning application—provided you abide by rules on height, size and placement.
However, some schemes lie outside these allowances:
Homes in Conservation Areas or Areas of Outstanding Natural Beauty face tighter controls.
Large Two-Storey or Wrap-Around Extensions almost always require full planning permission.
Listed Buildings need Listed Building Consent for any alteration, no matter how minor.
We handle permissions from start to finish with our in-house services, liaising with authorities in Christchurch, Southampton and Ringwood to keep your project on track.
How Can I Save Money On My House Extension In Poole?
Stretching your budget without cutting corners comes down to smart choices and the right partner.
Keep the Design Simple: A clean, rectangular footprint costs far less than curves or quirky angles.
Use Standard-Size Fittings: Off-the-shelf windows and doors can save thousands compared to bespoke.
Prioritise Key Finishes: Spend on elements that catch the eye (think flooring or worktops) and choose more economical options for things like lighting or paint.
Work With a Full-Service Builder: Bringing design, construction and decorating under one roof prevents delays and miscommunication. Hallmoore Developments secures trade discounts and keeps everything coordinated with our in-house services, saving you time and money.
How Long Does A Typical House Extension Take To Build In Southampton?
On-site, a straightforward single-storey rear extension usually takes about 10–12 weeks from foundation to finish.
For bigger projects—say a two-storey or wrap-around—you’re looking at 16–24 weeks on site. Bear in mind the design, structural drawings and planning stages often add several months before builders even arrive. We provide each client with a detailed, stage-by-stage timeline so you always know what’s coming next.
Ready to discuss the cost of your house extension in Highcliffe, Bournemouth or anywhere across Hampshire and Dorset? The team at Hallmoore Developments is on hand with a transparent, no-obligation quote and guidance through every stage. Our in-house experts, including Gas Safe registered engineers, make sure your project finishes on time and on budget.
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