How Much Do House Extensions Cost?

The cost of building a house extension in the UK can fluctuate dramatically depending on project size, which materials you select, and the complexity of the structural plan. According to industry data, a single-storey rear extension often begins at £1,500 per square metre for a straightforward build, while many standard expansions fall in the £1,800–£2,500 per square metre range. If you incorporate high-spec steel beams, designer glazing, or an upscale interior finish, totals can climb beyond £3,000 per square metre.

In Tower Hamlets, located in East London and covering areas like Whitechapel, Bethnal Green, Canary Wharf, and Limehouse, labour costs typically trend from moderate to high, reflecting ongoing regeneration and proximity to central business hubs. If your property is an older Victorian terrace in Bow or a 20th-century apartment near Shadwell, you might face extra structural measures—like underpinning or damp remediation—that boost final expenses. Large expansions can land between £40,000 and £100,000+, while smaller side-return or single-storey additions may be more economical. Multi-level or very lavish designs surpass typical cost thresholds if advanced engineering or top-tier decor is specified, and if you add or move a kitchen or bathroom, anticipate extra plumbing, electrical, and waterproofing efforts inflating costs.

When gathering contractor quotations, make sure each one includes foundation tasks, the structural assembly, roofing, fittings, finishing, labour overhead, etc. Also check if VAT—commonly 20%—is included or separate. Although renovation websites and magazines provide general references, accurate estimates demand multiple quotes from trustworthy local builders, assessed meticulously 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.

Tower Hamlets

Tower Hamlets is a diverse borough in East London, spanning from the high-rise financial district at Canary Wharf to historic areas like Spitalfields, Wapping, and Bow. Many Victorian terraces in Bethnal Green or Bow see single-storey rear expansions to transform cramped ground floors into open-plan living. In contrast, newer flats around Limehouse or the Isle of Dogs might adapt their interior spaces differently, occasionally creating small side extensions on ground-floor apartments with garden access—though these are less frequent. Loft conversions are still popular in pitched-roof dwellings near Mile End, turning attics into extra bedrooms or home offices. Basements, while not as common, do appear in certain affluent or historically significant roads near Whitechapel or Wapping, though water table and engineering concerns can raise the cost.

Local contractors mention that Tower Hamlets roads, particularly around Whitechapel High Street or near Canary Wharf, can experience significant traffic and parking constraints, so scheduling skip deliveries midmorning is wise. Labour fees vary from moderate in some residential pockets to higher in regeneration zones near the financial district. A well-planned extension can notably enhance daily comfort and property desirability, especially near strong transport links such as the DLR or District line. If you share boundaries in a terrace or live in a listed building (like some found in Stepney), open dialogues with neighbours and checking with the council early helps prevent party-wall or heritage conflicts.

Whether you aim to enlarge a Victorian terrace in Bethnal Green or adapt a ground-floor unit in Poplar, adjusting your extension plan to Tower Hamlets’ local environment and potential conservation rules typically eases the path toward official approvals.

Getting Started

Before breaking ground, settle on the kind of extension that best suits your Tower Hamlets property. A single-storey rear expansion is common for opening up an older kitchen-diner layout. A double storey approach increases living space on both floors, often adding a new bedroom or upstairs bathroom. A side extension can reclaim narrow land next to a terrace, if available. Should outward expansion be restricted, consider a loft or basement—though basements remain infrequent in Tower Hamlets outside certain prime roads, while loft conversions are more standard across pitched-roof Victorians in areas like Bow or Mile End.

Robust planning from the start curbs mid-project slowdowns. Develop a thorough budget referencing standard trade fees and typical material costs, plus a cushion for unexpected structural or finishing upgrades. If your design involves major structural changes—like eliminating substantial load-bearing walls—hiring an architect or building designer is often warranted. Some contractors provide design-and-build services but generally need initial sketches or partial planning consents for accurate quotes. Many owners in Tower Hamlets hire an architect first, then gather estimates from suitable builders.

It’s also important to organise a contractor well in advance, as reputable local teams frequently have packed timetables—particularly if you’re near Canary Wharf or around times of local development surges. Collecting multiple quotes early allows you to parse cost breakdowns, check references thoroughly, and choose a builder aligned with your budget and aesthetic. A skilled contractor might also refine your scheme—for instance, suggesting extra rooflights or adjusting an internal hallway to fit a discreet WC.

Project Management

You typically organise an extension in one of two approaches:

1. Single contract (design-and-build or main contractor)
   You sign a single overarching agreement with a building company that conducts or coordinates everything—foundation excavation, structural frames, electrics, plumbing, roofing, finishing. They subcontract trades, typically adding a 10–15% management fee. This unifies scheduling, giving you one main contact.
2. Multi-trade or split contract
   You personally employ groundworkers, carpenters, roofers, electricians, plumbers, etc. Although you save on the main contractor’s markup, you manage each trade’s timeline. If one trade finishes late, subsequent tasks might pause, adding stress or cost. This setup suits owners with the capacity to check progress and manage trades daily or weekly.

For bigger expansions in Tower Hamlets, single-contractor routes are common, especially for owners who prefer minimal day-to-day involvement in scheduling. If you pick multi-trade, ensure you can frequently visit the site and maintain close oversight of deliveries and tasks.

Do I Need Planning Permission?

Whether planning permission is necessary depends on your extension’s dimensions, height, and location on the plot. Under Permitted Development Rights, you can sometimes enlarge a house without lodging a planning application, so long as your design stays within certain size bounds. If it extends beyond those, a householder planning permission request is required.

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.

Parts of Tower Hamlets—like Spitalfields or some riverside enclaves—have conservation or heritage overlays, removing or limiting PD in certain streets. Checking Tower Hamlets Council’s planning guidelines or a planning consultant clarifies if your extension is PD or needs formal permission early on.

Do I Need Planning Permission For A New Storey?

Loft conversions altering rooflines or adding dormers generally require planning permission. Yet adding a new storey can be permitted development if you satisfy strict criteria and file a prior approval to the borough’s planning office. Otherwise, Householder/Full Planning Permission is standard. If your property meets the criteria, the bullet points below define those constraints:

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.

Additional completion rules might also apply. In many Tower Hamlets terraces, consistent roof lines or local design guidelines can shape the feasibility of adding entire new storeys.

Do I Need Planning Permission For A New Basement?

Constructing a new basement typically requires planning permission, and excavation under your property similarly often triggers permission due to the project’s scale. Engaging with Tower Hamlets Council’s planning office early clarifies local restrictions—particularly in historically sensitive zones near Spitalfields or near the Thames in Wapping. Basements represent one of the most expensive expansions, so even if official planning consent might not be mandated in certain scenarios, Building Regulations remain essential to uphold structural robustness, damp proofing, fire safety, and so forth.

Check local constraints surpassing PD expansions—some roads in Whitechapel or near Limehouse Basin might forbid or limit underground work. While basements are less frequent in typical terraced areas, more affluent pockets along riverside developments might adopt them if outward space is restricted.

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 a building regulations application. For simpler jobs, you can serve a Building notice, but more extensive builds typically demand a Full Plans Application, wherein you provide detailed specifications for approval prior to any construction. A Building Notice sees inspectors validate the work as it proceeds.

It’s also worth noting that tasks involving electrical, window fitting, plumbing, or heating systems may be carried out by professionals who are registered under competent person schemes (like NICEIC for electrics or FENSA for windows), allowing them to self-certify compliance instead of requiring separate building control checks.

A Full Plans Application commonly exposes design or safety flaws before work starts, while a Building Notice might suffice for straightforward projects. Either route, building control’s final endorsement confirms your completed extension meets code standards.

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

Whereas planning permission explores whether the extensions meets local and national planning requirements, building control ensures the structural soundness and regulatory compliance of your build.

Even if your Tower Hamlets extension falls under PD or obtains official permission, you must still satisfy building regulations—for example, ensuring stable foundations, correct insulation, correct ventilation, etc. With older Victorian or Edwardian terraces in areas like Bow or Bethnal Green, verifying new loads won’t compromise existing walls is crucial.

DIY Contribution

Homeowners sometimes envision handling parts of their extension themselves. Painting, decorating, or yard work can be plausible DIY tasks if you have the experience. Doing your own demolition, up to a point, may also be feasible—if you verify which walls are structurally significant and follow safety protocols.

But tasks including gas lines, rewiring, or structural modifications almost always call for qualified professionals. Errors might threaten safety or incur big rework costs. Realistically judge your skills; overreaching can stall progress. Builders may need to wait if your portion runs late, elevating total costs. If you want partial DIY, seeking professional advice first helps prevent large pitfalls.

In Tower Hamlets, partial DIY frequently surfaces at the finishing stage—like painting walls or refining outdoor spaces—once the main shell is completed. Attempting advanced structural or mechanical tasks alone jeopardises official checks or compromises final quality.

Do I Need An Architect?

If your extension is relatively small or simple, a structural engineer or design professional might suffice. For larger, more complicated layouts, though, an architect often brings real advantages. Competent architects integrate aesthetic form, daily function, and cohesive transitions between existing and new rooms.

They can also confirm if your plan is PD-eligible or needs a planning application. While employing an architect pushes up initial fees, it frequently forestalls mid-project design errors that inflate budgets.

Tower Hamlets includes modern high-rises around Canary Wharf, older terraces in Bow, and 19th-century properties near Wapping. An architect might craft partial glass roofs or folding wall solutions to unify a period exterior with a contemporary interior, reflecting the borough’s blend of old and new.

How Long Does It Take To Build An Extension?

Forming a practical schedule is crucial for a smooth build. A smaller single-storey rear project—especially if it’s straightforward, typical in materials, and PD-approved—could wrap up in just weeks once ground and structural tasks begin. Larger expansions, multi-level or multi-room, might take several months to half a year or more, shaped by how intricate the design is and how many trades you engage.

At times, you may consider relocating temporarily if supporting walls are demolished or if vital utilities are disrupted. Even if you remain at home, you’ll face dust, noise, and limited access to certain rooms.

It’s prudent to plan extra time for possible delays. Inclement weather can hamper exterior work, inspectors might call for small plan changes, or deliveries might arrive late. Coordinating a realistic timeline with your contractor keeps stress down, and finishing earlier than anticipated is always a bonus. Keeping a financial contingency helps handle hidden structural demands or finishing changes discovered mid-project.

Tower Hamlets roads near Whitechapel High Street, Mile End Road, or the busy Canary Wharf area can be heavily trafficked, so skip drop-offs typically occur midmorning. Altering your internal finishes or structural layout partway through can also shift your final completion date.

Step By Step

Though taking on an extension is formidable, with careful planning, reliable builders, and a rigorous budget, it can succeed. Whether you desire a more spacious ground-floor area, extra upstairs rooms, or even a basement, watch each stage closely and anticipate frequent 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. Fix any remaining flaws prior to final payment. Keep building control certificates, warranties, and compliance records for future property transactions or refinancing.

Once your extension in Tower Hamlets finalises and passes official checks, you can enjoy a bigger, more functional interior. Whether you formed a bright rear lounge or built a second floor with bedrooms, it generally boosts comfort and property value, particularly in locations benefitting from Crossrail, the DLR, or cultural hotspots near Brick Lane. A snagging survey ensures finishing mistakes—small cracks, uneven paint lines—are corrected. Storing building control documents and warranties demonstrates adherence to regulations, reassuring potential buyers or lenders if you decide to move later. Your newly enlarged Tower Hamlets home can then serve your evolving needs well into the future.