How Much Do House Extensions Cost?

The total expense of extending a house in the UK depends on factors such as project scale, chosen materials, and construction complexity. Industry data shows that a single-storey rear extension can begin at around £1,500 per square metre for a simpler approach, with many standard designs falling in the £1,800–£2,500 per square metre range. If you incorporate custom steel frameworks, high-spec glazing, or premium finishes, those prices may well climb beyond £3,000 per square metre.

In Croydon, local labour costs sometimes come in below central-London rates, which could let you spend more on refined finishes or specialist glazing. However, if your property is older, especially a 1930s semi or a Victorian-era house, you might need reinforced foundations or structural tweaks, raising overall costs. A larger extension frequently sits between £40,000 and £100,000+, whereas a narrower side addition might be cheaper, and multi-level projects or luxurious interiors could exceed typical boundaries if structural engineering is complex. Variables like local trade fees, design intricacy, and incorporating kitchens or bathrooms all affect your final total. Should you plan a new kitchen or bathroom, remember that added plumbing, electrics, and waterproofing drive your budget higher.

When you compare quotes, ensure each builder’s bid covers everything—foundation tasks, structural work, roofing, fixtures, finishing, plus labour and overhead. Check if VAT (commonly 20%) is included or extra to avoid last-minute surprises. While cost guides from magazines and websites offer broad figures, the best approach is collecting detailed estimates from reliable contractors and analysing them line by line.

Different Types Of Extensions

There are also different requirements for different extensions. Under is a list of the different types of house extensions:

Side extensions
Single storey extensions
Extensions more than one storey

They each have their own specific limits concerning such as rear extensions requirements, height, roofing and windows. For extensions of more than one storey, there is for example a requirement that roof pitch must match the existing house as far as practicable.

Croydon

Croydon, in south London, blends older residential areas with modern developments, making it one of the largest and most varied boroughs. Many households here extend single-storey to unite a cramped kitchen and separate dining area, forging a brighter, more open-plan design. Others look to side extensions to make use of narrow spaces, or to loft conversions if outward expansion is limited—particularly in classic 1930s semis found around South Croydon or Addiscombe. Basements can appear in some parts of Croydon, though the varied ground conditions or sloping plots in areas like Purley and Kenley may demand specialist engineering.

Local builders warn that Croydon roads, particularly near major commuter routes like the A23, can be busy, so timing deliveries mid-morning might help. Labour charges, though lower than central-borough levels, can allow owners to invest in refined finishes or modern glazing solutions. Still, you may face added planning demands if you live in Croydon’s conservation enclaves around places like Norwood Grove. For many, the upside is an improved day-to-day experience—extra living space, more cohesive layouts—and typically a value boost if your property is near strong transport links like East Croydon station. Checking with neighbours early for boundary lines or party-wall concerns can prevent friction once construction begins.

Whether you envision a simple extension to open up a rear kitchen or a more elaborate project spanning multiple floors, factoring in Croydon’s local constraints helps you meet planning requirements and shape a design that suits the borough’s suburban character.

Getting Started

Before you get to the building phase, choose which extension layout best suits your property. A single-storey rear design can boost a small kitchen-diner, while a double storey can deliver extra upstairs bedrooms. Some owners might opt for a side extension if there’s driveway space, and others attempt basements or loft conversions for extra floors. Basements in Croydon can be technically challenging, depending on the area’s soil and potential slopes.

A thorough planning stage often saves time mid-project. Start by creating a detailed budget, referencing average labour fees and material costs, plus a contingency for hidden structural needs or higher-end finishes. If your plan requires noticeable structural changes, hiring an architect or trained designer can be beneficial. Some builders provide design-and-build, but usually require preliminary drawings or partial planning permissions to quote precisely. Many Croydon owners first hire an architect for a clear design, then gather builder bids.

Also, secure a dependable contractor early, as strong teams fill their rosters fast. Gathering estimates sooner allows you to compare costs, check references, and select someone who aligns with your budget. An experienced firm might also propose enhancements—like an extra window or a pivot in your layout to incorporate a utility area.

Project Management

You can typically run your extension project in one of two ways:

• Single contract (design-and-build or main contractor):
  You enter a single contract with a building firm that coordinates all tasks: foundation digging, structural carpentry, plumbing, electrics. They subcontract where necessary, typically adding 10–15% for management. This structure offers cohesive planning and only one major contact for you.
• Multi-trade or split contract:
  You manage each trade yourself—groundworkers, bricklayers, roofers, electricians, plumbers, etc. Although you avoid the main contractor’s markup, you must handle scheduling. If a single trade is delayed, subsequent tasks may be idle. Unless you have ample spare time or some construction knowledge, this approach can be stressful.

For larger or trickier extensions in Croydon, families often prefer a single-contractor route, sparing them day-to-day oversight. If you do multi-trade, confirm you can frequently check progress to sustain momentum across different trades.

Do I Need Planning Permission?

Whether you need planning permission is influenced by your extension’s overall size, height, and property location. Under Permitted Development Rights, you may expand without making a formal planning application, as long as your project fits specific dimensions and stipulations. However, if your design stretches beyond these, you typically must lodge a householder planning permission.

Under are the general rules that apply to all extensions:
Only half the area of land around the "original house" can be covered by extensions or other buildings.
Extensions cannot be higher than the highest part of the existing roof; or higher at the eaves than the existing eaves.
Where the extension comes within two metres of the boundary the height at the eaves cannot exceed three metres.
Extension cannot be built forward of the ‘principal elevation’ or, where it fronts a highway, the ‘side elevation’.
The work cannot include:
verandas, balconies or raised platforms.
a microwave antenna (e.g. TV aerial or satellite dish).
a chimney, flue or soil and vent pipe.
any alteration to the roof of the existing house.
On Article 2(3) designated land the work cannot include cladding of the exterior.
The materials used in any exterior work must be of a similar appearance to those on the exterior of the existing house.
Source: Planning Portal.

In Croydon, if you’re near a designated conservation area or an Article 4 locale, you might encounter stricter guidelines. Always check with council planning staff to confirm you meet PD or need a formal application.

Do I Need Planning Permission For A New Storey?

Loft extensions with dormer windows or increasing roof height often call for planning consent. Nonetheless, it can be permitted development to add an extra storey if precise criteria are fulfilled, alongside submitting a prior approval application to your local authority. Otherwise, a Householder/Full Planning Permission route is required. If your property meets these standards, the bullet points below set out key restrictions:

Number of additional storeys:
One storey can be added to a single storey house
Two storeys can be added if the house has more than one storey.

Height increases:
The house cannot exceed 18 metres in total height
Each added storey cannot add more than 3.5 metres to the total height
If not detached (e.g. terrace or semi) the total height cannot be more than 3.5 metres higher than the next highest building that the house is attached to, adjoins, or is in the same row as.
The additional storeys must be constructed on the principal part of the house*
The additional storeys must not exceed 3 metres in height or the height of any existing storey in the principal part of the house (measured internally from floor to ceiling)
Engineering operations must only include works within the existing curtilage of the house to strengthen existing walls and foundations
The materials used must be of a similar appearance to those used in the construction of the exterior of the current house
Windows must not be placed in any wall or roof slope forming a side elevation of the house.

Certain further conditions might apply after you’re done building. Clarify with Croydon’s planning officials to avoid clashing with uniform roof shapes or local streetscapes.

Do I Need Planning Permission For A New Basement?

Creating a new basement typically demands planning permission, and excavating below ground is also likely to require planning permission, due to the extent of the work. It’s helpful to discuss your ideas with the local planning authority early, so you know their requirements. Basement construction is also extensive; even without explicit planning approval, you must still comply with Building Regulations to ensure structural integrity, safe escape routes, proper ventilation, fire safety, and more.

Always research any rules potentially affecting your project and home. Sometimes, conditions from earlier or local planning decisions can override Permitted Development. Go through Croydon Council’s guidance or consult a planning professional for certainty.

In Croydon, basements aren’t as widespread as in some older central boroughs, yet a few property owners do choose partial basements or sub-ground rooms if outward or upward extension is constrained. These projects cost more and often demand in-depth ground surveys.

Remember Building Regulations Application

Regardless of the size and shape of your extension, it must meet building regulations requirements. This is also regardless of whether you need planning permission or not.

You will need to submit a building regulations application. For smaller projects you can submit a Building notice but for larger extensions you’ll probably need a Full Plans Application. In this case full details of the proposed work will be submitted for approval before the work begins. With a Building Notice an inspector will inspect and approve the work as it is performed.

A Full Plans Application can uncover potential issues—like insufficient beams or ventilation—well before building starts, while a Building Notice can suit smaller expansions, but you risk on-site changes if inspectors spot design flaws mid-build.

What’s The Difference Between Planning Permission And Building Regulations Application?

Whereas planning permission assesses whether the extensions meets local and national requirements, building control concerns structural safety and regulations compliance.

Even if you don’t need a formal planning application (under Permitted Development rules), you must still obtain building regulations sign-off, confirming your extension is structurally sound, waterproofed, and insulated to modern standards. In Croydon, older homes can pose extra considerations for load-bearing walls or damp-proofing.

DIY Contribution

Homeowners sometimes consider tackling parts of an extension themselves. Painting, decorating, or landscaping can be good DIY tasks if you have the skills and time. Doing your own demolition, to an extent, can also be feasible—provided you understand which walls are load-bearing and follow safety precautions.

However, tasks such as electrical installation, gas connections, and structural changes almost always require qualified professionals. Mistakes in these areas can be costly and dangerous. Being realistic about your abilities is crucial; if you overcommit, you risk causing delays. Builders may need to pause until you finish a particular job, which can add to your final bill. If you’re determined to do some work yourself, consider hiring a professional for a consultation, as their input can help you avoid pitfalls.

In Croydon, partial DIY usually focuses on decorating or final landscaping once the main shell is finished. This approach lets experts handle structural or mechanical tasks that, if done incorrectly, could hold up the entire build.

Do I Need An Architect?

If your extension is fairly basic, a structural engineer or building designer might suffice. Yet for many bigger or more challenging projects, an architect can be immensely helpful. Talented architects look beyond visual elements to integrate practical factors—like interior traffic flow, daylight, and ensuring new rooms mesh with existing ones or the garden.

They can also direct you through planning consent or permitted development queries. While hiring an architect involves an added fee, their perspective often eliminates design flaws early, producing a more cohesive final result.

Croydon includes pockets of 1930s suburbia as well as Victorian terraced streets, so melding older exteriors with a contemporary extension can be tricky. An architect might propose complementary brick or roof designs, or a strategic selection of windows and rooflights.

How Long Does It Take To Build An Extension?

Scheduling a realistic timeframe helps you oversee the project’s progress. A basic single-storey addition—a small rear extension, for instance—could complete within weeks if the design is simple, the materials are standard, and it’s under permitted development. Larger expansions, multi-level or multi-room, might stretch from a few months to half a year or more, depending on overall scope.

Sometimes, you may need to vacate the house temporarily if major structural alterations disrupt plumbing or electrics. Even if you remain, expect dust, noise, and limited access in certain areas.

Keeping a buffer is wise, as delays can stem from severe weather, planning inspector adjustments, or late material shipments. Coordinating a workable schedule with your builder helps reduce stress, and finishing early is always a plus. Equally, a financial reserve addresses any mid-project changes or hidden structural tasks.

Croydon experiences busy commuter routes, so skip drop-offs or deliveries often happen late morning or midday to dodge peak traffic. If you choose unique materials or revise aspects mid-build, your end date may also shift.

House Extensions Step By Step

While adding an extension is a notable undertaking, with solid planning, skilled trades, and a practical budget, you can succeed. Whether you desire an enlarged kitchen-living zone, more bedrooms, or a loft, keep track of each phase and remain alert to typical issues.

1. Start by confirming what you want to achieve—more natural light, a larger social area, or additional bedrooms.
2. Then decide how best to organise the project.
3. Check if you need planning permission and what kind of building regulations application you need to send in.
4. Gather quotes from at least three builders if possible, ensuring each has a solid track record and good references.
5. Check that their quotes are like-for-like in terms of scope.
6. Factor in the cost of planning applications, building control fees, and professional services such as architectural drawings or structural engineering.
7. Then develop a realistic schedule, communicate frequently with your chosen contractor, and keep a close eye on both time and budget.
8. Finally, as the build nears completion, consider a thorough inspection—often called a snagging survey—conducted alongside your main contractor or an independent professional. Any lingering faults should be addressed before you pay the final bill. Keep documentation, such as building control certifications and warranties, safe for any future sale or mortgage changes.

When all building phases pass inspection, you’ll enjoy a bigger, more functional living environment. Whether you’ve fashioned an open-plan ground floor or added a new level, the extension can add comfort and boost resale value. Croydon owners often appreciate how expansions let them stay near local schools and commuter lines while modernising older interiors. A snagging survey can reveal small flaws—paint mismatch, fine cracks—and let the contractor fix them before final payment. Storing official compliance records demonstrates to lenders or potential buyers that everything was done properly. With that, your newly enlarged Croydon home should serve you well for years to come.