How Much Do House Extensions Cost?

Across the UK, the expense of adding an extension varies substantially, shaped by size, materials, and overall complexity. Sources suggest a single-storey rear extension can start around £1,500 per square metre for a simpler design, while more standard projects typically range from £1,800–£2,500 per square metre. If you opt for custom glazing, advanced steel elements, or luxurious finishes, your spend could quickly surpass £3,000 per square metre.

Many owners in Barking and Dagenham find that labour rates are somewhat more affordable than in core London areas, giving them scope to invest in upgraded interiors or high-quality doors and windows. Yet older houses in the borough can bring extra structural costs—especially if the foundations must be fortified or if clay-based soil complicates groundworks. Consequently, a larger extension might fall between £40,000 and £100,000+, though a narrower side-return scheme could cost less, while highly intricate multi-storey builds exceed typical price brackets if specialised finishes or complex layouts are chosen. Elements like design complexity, local trade fees, and the inclusion of a bathroom or kitchen also affect your final tab. Adding plumbing, waterproofing, and electric lines for these rooms normally leads to bigger overall costs.

Whenever you compare quotations, ensure each covers excavating foundations, structural build, roofing, fittings, and finishing tasks. Likewise, confirm labour, materials, and management overhead. Ask if VAT—commonly 20%—is included, to avoid sudden extra charges. While magazines and home-improvement websites provide approximate cost benchmarks, accurate budgeting stems from collecting multiple quotations from established builders and comparing 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.

Barking and Dagenham

Barking and Dagenham is a borough located to the east of central London, known for a mix of older terraces, post-war builds, and more modern neighbourhood developments. Many householders here embrace single-storey rear expansions to connect living and kitchen areas, creating open layouts for modern lifestyles. Others find that side extensions reclaim underused passageways, or they choose loft conversions if ground-floor land is limited. In certain scenarios, a basement might prove viable, though it typically requires more intensive structural work.

Local contractors stress the importance of planning skip deliveries or material arrivals outside peak traffic hours, given some busier roads in the borough. Labour charges are often lower than in central zones, allowing some homeowners to fit higher-quality finishes within their budget. Nonetheless, pockets of Barking and Dagenham may include conservation areas or local restrictions that affect outward-facing changes. Many owners who extend discover both enhanced day-to-day comfort and stronger property value if they reside near good transport links such as the District line or Overground services.

Whether you aim for a simple expansion to create a larger kitchen-diner or a more extensive two-storey reconfiguration, adapt your design carefully to Barking and Dagenham's local context. Approvals could be simpler than in central boroughs, but always check early about party walls or boundary conditions, ensuring a smoother route to completion.

Getting Started

Before construction begins, decide exactly which type of extension best suits your objectives. You might choose a single-storey addition, a double storey structure, a side or wrap-around build, or even a loft or basement conversion if expanding outward is not feasible. Basements can be beneficial if you cannot enlarge at ground level, but they tend to be more involved.

Substantial planning at the outset helps minimise scheduling issues. Start by preparing a detailed, realistic budget, referencing average material and labour charges. Include some contingency for upscale finishes or surprises in the foundational or structural stages. If your design involves major structural shifts, consider hiring an architect or qualified designer. A few UK building firms offer design-and-build services, but normally they require preliminary sketches or partial planning approval to quote precisely. Typically, homeowners engage an architect first, then collect quotes from builders.

It’s also wise to look for a builder early, as reputable teams are often in high demand. Gathering quotes soon lets you compare costs, talk with references, and lock in your contractor. A capable builder can also refine your initial ideas—for instance, proposing an additional window for sunlight or optimising the layout for storage.

Project Management

When organising an extension, most homeowners pick one of two methods:

• Single contract (design-and-build or main-contractor):
  You sign a single agreement with a building firm that handles everything, including structural tasks, plumbing, and electrics. They typically subcontract specialist trades, charging around 10–15% markup for coordination. This approach consolidates scheduling and ensures you have one main contact.
• Multi-trade or split contract:
  You directly manage each trade—foundations, carpentry, roofers, electricians, plumbers, and so forth. Although it might appear cheaper, it requires keen project management, ensuring each element lines up smoothly. If a particular trade lags, follow-up trades may be delayed, risking budget escalation. Handling this route means you’ll need considerable construction knowledge or time.

For extensive or intricate builds, many Barking and Dagenham owners lean toward a single-contractor model, letting professionals manage each trade. Those with strong organisational skills or who know reliable local trades may prefer multi-trade, but it’s more hands-on.

Do I Need Planning Permission?

Whether you need planning permission depends on your proposed extension’s size, height, and location on the property. Under Permitted Development Rights you are allowed to extend a house without needing to apply for planning permission if specific limitations and conditions criteria are met. However, if your project goes beyond these allowances, an application for householder planning permission will likely be needed.

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 Barking and Dagenham, some areas under regeneration or with existing planning conditions might impose additional checks. Always confirm with local planning staff whether your project qualifies as PD or if you must submit a householder permission request.

Do I Need Planning Permission For A New Storey?

Loft extensions involving dormer windows or raising the roof often require planning permission. Adding a new storey is considered permitted development, meaning planning permission is not required, if strict criteria are met. This is also contingent on an application for the local authority’s prior approval. Otherwise, an application for Householder/Full Planning Permission will be needed. If your house meets the requirements, the limits on the proposed development is as follows:

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.

There are also requirements following completion of development. Even if your build meets each criterion, double-check with Barking and Dagenham’s planning team to avoid confusion—especially in uniformly designed streets.

Do I Need Planning Permission For A New Basement?

Creation of a new basement will usually need planning permission, and excavating to create a basement is also likely to require planning permission due to the major works required. It’s a good idea to discuss your project with your local planning authority to understand requirements before applying. Basement excavation is similarly complex. Even if the project does not require explicit planning approval, you still must comply with the Building Regulations to ensure the extension is structurally sound and meets standards for escape routes, ventilation, damp proofing, fire safety, and more.

Always check any and all possible regulations that may apply in your area and for your specific home. In some cases, an extension that would normally fall under Permitted Development can be restricted by previous and local planning conditions. Check local council guidance or consult a planning expert to be certain.

In Barking and Dagenham, basements are comparatively rare, but some households consider partial below-ground levels if outward or upward development is not an option. Prepare for higher build costs and potentially longer timelines if you go this route.

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 detect problems before work starts, while a Building Notice is often fine for simpler expansions. In either method, building control must grant approval to confirm you have adhered to codes for stability, fire protection, insulation, etc.

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 no planning application is mandatory (due to Permitted Development), you must still comply with building regulations to make sure foundations, ventilation, and other aspects meet present standards. In Barking andDagenham, older houses can need extra checks to handle expansions safely.

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 Barking and Dagenham, partial DIY typically occurs after the core shell is built, when owners add finishing touches or decorative elements. Handling major structural or mechanical projects yourself could interrupt the entire workflow if anything is off-schedule.

Do I Need An Architect?

If your design is straightforward, you might rely on a structural engineer or a professional building designer rather than a fully chartered architect. Yet for many extension projects, especially bigger or more complex ones, engaging an architect can be hugely beneficial. Good architects consider not only aesthetics but also practicalities such as natural light, flow between rooms, and how the extension integrates with your existing house and garden.

They can also guide you through planning permission or permitted development applications. While an architect does mean extra upfront costs, their expertise often pays for itself by creating a better-functioning layout and avoiding design errors that could cause problems later.

Barking and Dagenham contains several areas where mid-century houses might require thoughtful upgrading to fit contemporary lifestyles. Architects can propose rooflights, sliding doors, or innovative internal partitions that amplify space and cohesiveness.

How Long Does It Take To Build An Extension?

A timeline is vital for keeping everything under control. A modest extension—like a small single-storey rear addition—might take only weeks once on-site work begins, especially if it’s within permitted development, relies on simple design features, and uses available materials. Larger schemes, such as multi-room expansions or multi-level builds, could stretch from several months to over half a year, shaped by complexity and how many trades you need.

In some cases, a temporary move-out might be necessary if major structural tasks cut off utilities or involve tearing out principal walls. Even if you remain, noise, dust, and restricted room access can be expected.

Always factor in a buffer. Delays occur due to poor weather halting exterior tasks, inspectors requesting minor changes, or supply shipments arriving late. Planning a realistic schedule with the contractor eases pressure. Equally, setting aside contingency funds handles mid-project adjustments or unanticipated structural fixes.

In Barking and Dagenham, skip placement and delivery times can be complicated by main roads, so midday scheduling often works best. If you alter finishes or source unique materials mid-project, you can push back completion even further.

House Extensions Step By Step

Undertaking an extension is significant, but with a solid plan, capable professionals, and a sensible budget, there’s no reason success should elude you. Whether you want a bigger kitchen-diner, another bedroom, or a loft conversion, it pays to grasp each phase and watch out for potential stumbling blocks.

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 unresolved issues should be corrected before issuing the last payment. Keep any building control certificates, warranties, and other paperwork in a safe place, should you later sell or remortgage.

Once the extension receives its final approval, you can enjoy a larger, more functional layout. Whether you have fashioned a bright rear living area or added extra floors, a well-executed project adds both convenience and potential future value to your property. In Barking and Dagenham, a family-friendly borough with evolving transport links, an expanded home often stands out if you ever decide to sell. A snagging survey ensures that small defects—like hairline cracks, misaligned paint lines, or uneven floor finishes—are spotted and resolved. Retaining evidence of compliance, such as building regs approvals and warranties, demonstrates to prospective buyers or mortgage lenders that everything was done correctly. With that, your new living space in Barking and Dagenham is ready to enrich your day-to-day life for years to come.