How much does a house extensions cost?

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The average cost of a house extension is between £45,000 - £75,000. This guide is here to walk you through every step, ensuring you have all the information you need to make informed decisions. Keep in mind that the home extension costs in this article are correct as of 2024.

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When you decide to extend your home, you're not just creating more space; you're making a significant investment in your future comfort and lifestyle. However, this journey comes with its unique set of financial considerations, and understanding these is crucial to a stress-free project.

We’ve spoken to some of the expert extension builders on MyBuilder to get an accurate price guide for home extension jobs, including a handy house extension cost calculator. Here’s what you need to know.

We'll cover the following topics in this pricing guide:

  1. Why Opt for a House Extension?
  2. Average Costs of House Extensions
  3. Factors Affecting the Average House Extension Cost
  4. Home Extension Types
  5. How to Save on House Extension Costs?
  6. How long does a house extension project take?
  7. Additional Costs
  8. Your house extension checklist
  9. FAQ

Why opt for a house extension?

Choosing to extend your home is a decision often sparked by the desire for more space, but the benefits extend far beyond the additional square footage. A home extension provides the opportunity to tailor your living environment to your evolving needs, be it an expanding family, the necessity for a home office, or a space for relaxation. It's a chance to infuse new life into your home, enhancing comfort, style, and functionality. Moreover, an extension is a sound investment, significantly boosting the property's market value. It offers a cost-effective alternative to moving, saving you from the hassles and expenses of selling your current home, buying a new one, and relocating. Ultimately, a home extension is not just an expansion of space; it's an enhancement of your living experience and a strategic step in future-proofing your property.

Average costs of house extensions

Venturing into a house extension project requires a clear understanding of the associated costs to ensure a smooth execution within your budget. On average, the cost of a house extension in the UK can range from £1,500 to £2,500 per square metre. An average extension of 30m2 is estimated between £45,000 to £75,000 However, this price can vary significantly based on several factors, including the size and type of extension, the materials selected, the geographical location of your property, and the complexity of the design. For instance, a single-storey extension is generally more cost-effective than a multi-storey project that requires additional structural support and materials. Furthermore, bespoke features or high-end finishes can also escalate costs. It's crucial to obtain detailed quotes from several contractors to gauge a realistic budget, and always factor in additional costs such as architectural services, planning permissions, and potential unforeseen expenses. By understanding these average costs, homeowners can embark on their extension projects with financial confidence and realistic expectations. Here's a table illustrating the average costs of house extensions, based on quality and size:

Quality of ExtensionSize (m²)Low Price RangeHigh Price RangeAverage Cost
Small extension20£40,000£55,000£45,000
Medium extension30£45,000£75,000£60,000
Large extension50£75,000£125,000£100,000
Prime extension30£65,000£90,000£77,500

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In this article, we have broken down different elements of an extension build and the different kind of costs involved, but the key underlying cost relates to the size of the extension being built.

These prices don’t include VAT, charged at 20%. The price bracket reflects the variance of materials used, the complexity of design, quality of finish and where in the UK you live.

This price covers the essential elements of the build, constructing the foundations, building the walls, insulating the new structure, fitting out with plasterboard, adding a subfloor, and installing a basic provision for plumbing and electrics.

It will not include any of the finishing elements, such as decoration or kitchen installation, which we cover later in this article.

Factors affecting the average house extension cost

When planning a house extension, grasping the multitude of factors that can affect the cost is essential. These elements don't just influence your budget; they also shape the planning, execution, and final outcome of your project. Let's unpack these factors to provide a clearer roadmap for your financial planning.

  • Size and scale: The most direct impact on your budget is the size of the extension. More square footage means more materials, more labor, and increased costs in almost every category. It's not just the floor area; the height and volume of the extension can also add complexity and cost, especially with multi-storey extensions requiring more intricate structural work.
  • Design complexity: A straightforward, rectangular room is simpler and, therefore, cheaper to build compared to a design with curves, multiple corners, or unique architectural features. Complex designs necessitate more specialized labor and materials, and potentially more planning permissions or inspections, all of which contribute to higher costs.
  • Material choices: The materials you select for everything from the construction (bricks, concrete, timber) to the finishes (flooring, tiles, paint) play a significant role in determining costs. Premium materials can elevate the look and durability of your extension but come with higher price tags. Balancing aesthetics, performance, and cost when choosing materials is a key part of the budgeting process.
  • Location: The geographical location of your property isn't just about the land. It's about the cost of living, the availability of tradespeople, and the logistics of getting materials to your site. For instance, building an extension in London is typically more expensive than in other parts of the UK due to higher labor costs, material costs, and general living expenses.
  • Labour costs: The tradespeople you hire for your project—from architects and surveyors to builders and electricians—will constitute a significant portion of your budget. Rates can vary widely based on experience, reputation, and demand. Remember, while it's important to consider cost, the cheapest quote isn't always the best. Quality workmanship ensures your extension's longevity and safety.
  • Site accessibility: If your property is difficult to access, it can increase costs. Challenges such as narrow roads, restricted parking, and the need for specialized machinery to transport materials can complicate the build process and stretch your budget.
  • Existing property structure: The condition and age of your existing property can influence costs. Older homes may require additional structural support, updated wiring, or other modifications to meet current building regulations, all adding to the overall expense.
  • Regulatory requirements: Obtaining planning permission, if necessary, involves application fees. Moreover, your build must comply with building regulations, which may necessitate additional spending on structural integrity, fire safety measures, insulation, and other standards set by the local authorities.

Home extension types

Each of these factors requires careful consideration and detailed planning. Understanding them doesn't just prepare you for the financial commitment involved; it also equips you with the knowledge to make informed decisions that affect the timeline, efficiency, and success of your extension project.

Embarking on a house extension project requires an understanding of the specific costs associated with the type of extension you're considering. Each extension type comes with its unique set of requirements, materials, and labor costs. Below, we dissect the financial implications of various extension types to help you navigate your budgeting process more effectively.

How much do single storey Extensions cost?

These are popular for their simplicity and the significant additional space they provide without the need for extensive structural modifications. The cost is usually determined by the size (per square metre), the complexity of the design, and the materials used. On average, you might expect to spend £1,500 to £2,000 per square metre.

How much do double storey extensions cost?

Offering even more space, these involve more complex structural and design work, reflecting in higher costs. These extensions typically range from £1,700 to £2,500 per square metre, influenced by the same factors as single-storey extensions but with added architectural, material, and regulatory considerations.

How much do conservatories cost?

These glass-heavy extensions are a way to enjoy the surrounding landscape while being sheltered. Costs can vary significantly based on size, glazing options, and construction materials, with a standard project potentially costing between £10,000 and £20,000.

How much do loft conversions cost?

Transforming an unused attic space into a functional room can be a cost-effective way of adding space. The price depends on the structural modifications needed, the type of room planned, and access construction, with costs ranging from £55,000 to £75,000.

How much do basement conversions cost?

Often the most complex and costly due to extensive excavation and waterproofing requirements, these projects can range from £1,250 to £2,000 per square metre, sometimes more if structural challenges arise.

How much do garage conversions cost?

If the structure is already sound, these can be a budget-friendly choice. The costs, generally between £10,000 and £20,000, involve interior renovations, insulation, and possibly adding windows or doors.

How much do orangeries cost?

More solid than conservatories and featuring a lantern roof, orangeries offer a balance between extension and conservatory. The intricate construction and materials can bring the cost to between £10,000 and £100,000.

Each extension type serves different needs and aesthetics, and understanding the associated costs ensures you match your vision with your budget effectively. It's always prudent to factor in a buffer for unforeseen expenses, ensuring your project runs smoothly.

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How to save on house extension Costs?

Venturing into a house extension doesn't have to strain your finances beyond reach. With strategic planning, informed choices, and a bit of insider know-how, you can significantly pare down expenses without compromising on your plan. First, consider simplifying your design; complex structures require more materials and labor, whereas streamlined, functional designs can be just as impactful at a fraction of the cost. Opt for cost-effective but high-quality materials that offer durability and aesthetic appeal without the hefty price tag. Sometimes, the most modest materials can make a significant impact with the right design and craftsmanship.

Another cost-cutter is taking on some DIY tasks. While certain jobs require professional hands, others, like preliminary site clearing, demolition, or even painting, can be managed personally, slashing labor costs. Additionally, timing your project strategically can have financial benefits. Prices for materials and labor can fluctuate depending on the season, with potential savings during off-peak periods. It's also prudent to obtain multiple quotes from contractors to ensure competitive pricing, but remember, the cheapest isn't always the best. Balance cost considerations with the contractor's experience, reliability, and professional rapport.

Lastly, a well-defined project scope and meticulous planning can prevent costly changes mid-project. Ensure you have a detailed, well-thought-out plan from the onset, and resist making alterations once construction commences. Unplanned changes can lead to delays, wasted materials, and additional labor costs. By adopting these cost-saving strategies, you can make your budget work harder for you, achieving the extension you desire without unnecessary extravagance.

How long does a house extension project take?

An extension building project goes through several stages of building, which are broken out below. Establishing individual prices for each section is difficult, as many builders will not separate costs for elements such as groundworks, which are rarely done in isolation from the rest of the project.

However, if you are having an extension built, many homeowners will agree to pay their tradespeople in stages, typically after some of the following elements are competed.

StageKey ActivitiesEstimated Timeframe
ConceptualizationVision setting, preliminary sketches, budget forecasting2-4 weeks
Design & planningDetailed architectural drawings, planning permissions4-8 weeks
Contractor selectionBidding, evaluation, and selection of builders3-6 weeks
Site preparationClearing site, setting up access and facilities1-2 weeks
Foundation workExcavation, laying foundations, damp proofing3-4 weeks
Building phaseStructural work, walls, roofing, windows, and doors6-12 weeks
Utilities & amenitiesElectrical, plumbing, heating installations2-4 weeks
Interior finishingPlastering, flooring, fixtures installation4-6 weeks
DecorationPainting, decorating, final touches2-3 weeks
Final inspection & handoverQuality checks, snagging, project handover1-2 weeks

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Embarking on your home extension journey in this structured manner allows for a transparent view of the project timeline, helping manage expectations and ensure each phase receives the attention it deserves. While these stages are sequential, some may overlap, and external factors can influence durations. Regular consultations with your architect and builder are essential to navigate through each phase effectively.


Additional house extension costs

While the primary expenses of a house extension are usually clear—covering aspects like materials, labor, and direct construction costs—several additional costs can surface during the project. These costs, often overlooked, are crucial for comprehensive budgeting and smooth execution of your extension. Here's a breakdown of these additional expenses and their potential impact on your overall budget.

Architectural services: Unless you're adopting a standard extension design, you might need an architect or a structural engineer. These professionals will draft the design, provide structural calculations, and may even help navigate the planning permission process.

Planning permission and building regulations: If your extension requires planning permission, there will be an application fee. Additionally, independent inspections might be necessary to ensure your project complies with building regulations.

Insurance: Undertaking a significant structural change to your home necessitates reviewing your insurance. You may need to increase your coverage during and after the construction, representing an additional cost.

Contingency fund: It's prudent to set aside a contingency fund, typically 10-15% of your total budget, to cover unforeseen issues like unexpected groundwork complications or mid-project changes.

VAT: Most building work and professional services will attract VAT, and it's vital to check whether quoted prices include or exclude VAT to avoid surprises.

Utility connections: If your extension involves adding a kitchen or bathroom, consider the costs of extending water, gas, or electricity to the new space.

Landscaping: Extending your house might necessitate landscaping work to restore the outdoor aesthetics once construction is complete.

Interior finishing and decoration: Beyond the structural work, there's the cost of painting, flooring, and furnishing the new space to make it livable and cohesive with the rest of your home.

Here's a table presenting the additional potential costs:

ActivityAdditional costs
Architectural servicesAbout 10% of construction costs
Planning permission£200 - £400
Building regulations£750 - £1,000
InsuranceVaries (contact insurer)
Contingency fund10-15% of construction costs
VAT20% of taxable services
Utility connections£500 - £2,000
Landscaping£500 - £3,000
Interior finishing and decoration£2,000 - £10,000

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These figures are estimates and can vary based on individual project specifics, location, and service providers. They serve as a guide to help you plan comprehensively, ensuring you're financially prepared for the journey ahead.

Your house extension checklist

When planning a house extension, it's easy to get lost in the excitement of creating new space. However, a successful project requires attention to detail and thorough preparation. Below is a handy checklist to ensure you've covered all bases, making the process as seamless as possible:

  • Define your vision: Clearly outline what you want from your extension, considering how it will improve your lifestyle and add value to your home.
  • Set a budget: Determine your financial capacity, including a contingency for unforeseen costs, ensuring your project doesn’t stall due to financial constraints.
  • Choose a design: Whether modern or traditional, decide on a design that complements your existing property and meets your functional needs.
  • Hire tradespeople: From architects and builders to surveyors, select experienced tradespeople with credible references.
  • Secure permissions: Check with local authorities to see if you need planning permission or if your project falls under permitted development.
  • Understand building regulations: Ensure your extension complies with building codes, focusing on safety, energy efficiency, and quality standards.
  • Plan for disruption: Prepare for how the construction phase might disrupt your daily life and plan accordingly.
  • Insurance and warranty: Update your home insurance to cover the new extension and ensure any new work is backed by a warranty.
  • Contract review: Have a legal expert review contracts with builders or subcontractors to protect your interests.
  • Final inspection: Before signing off, conduct a thorough inspection of the work against your initial plan and address any issues.


When delving into a house extension project, numerous questions arise, reflecting the complexity and significant investment of such an endeavor. Below, we address some of the most pertinent queries to equip you with the knowledge you need for a smooth, informed journey.

What is the first step in planning a house extension?

Begin with a clear vision of what you need from the extension, considering both functional requirements and aesthetic preferences. This step is followed by budget setting, hiring an architect, and understanding legal permissions.

How do I choose the right architect or builder?

Research and recommendations are key. Look for professionals with strong portfolios, check their references, and ensure they have experience in projects similar to yours. Don’t hesitate to conduct interviews to gauge compatibility.

Do all house extensions require planning permission?

Not always. Many fall under 'permitted development rights,' but this depends on various factors including the extension size, property location, and design. Always check with your local planning authority.

How can I ensure my budget covers all costs?

Be thorough in initial planning, account for potential overruns, and ensure your budget includes contingencies (usually 10-20% of the total cost). Regular communication with your builder can also help avoid unexpected costs.

What factors could delay my extension project?

Weather conditions, unexpected structural issues, changes in project scope, or delays in material supply can all impact timelines. Building during favorable weather seasons and detailed contract outlines can mitigate some risks.

How does a house extension impact my home insurance?

Inform your insurer about the extension, as it changes your policy conditions. You may need to adjust your coverage to include the new addition, both during construction and after completion.

What are the signs of a quality house extension job?

Look for seamless integration with the existing structure, high-quality materials, professional workmanship, adherence to the planned timeline, and no outstanding structural or aesthetic issues at handover.

Can I live on-site during the extension?

It’s possible, but consider the impact of construction noise, dust, and reduced privacy. Some homeowners find temporary accommodation to avoid the disruption.

What long-term maintenance will my extension require?

Regular upkeep depends on materials used and local climate. Generally, keep an eye on roofing, insulation, exterior paint, and structural elements to address any wear and tear promptly.

How do I handle disagreements with my builder or architect?

Open communication is crucial. Address issues promptly, refer to your contract, and consider mediation if you cannot reach a resolution. Documentation of all discussions and agreements is also highly advisable.