How Much Do House Extensions in Islington Cost?

In the UK, the price of a house extension can vary dramatically based on several factors—such as how large the design is, which materials you choose, and how structurally complex it is. According to industry data, a single-storey rear extension might start around £1,500 per square metre for a simple build, while many standard expansions fit in the £1,800–£2,500 per square metre bracket. Should you adopt custom steel beams, glazed walls, or high-end interior finishes, costs may push above £3,000 per square metre.

In Islington, a borough in north London known for its blend of historical terraces and modern apartments, labour rates generally rank on the higher side because of the proximity to central London and the popularity of housing there. If your house is a Victorian or Georgian terrace near Upper Street or Canonbury, you may face additional structural reinforcement to handle the new weight, pushing up costs. More spacious expansions can often land anywhere from £40,000 to £100,000+, while modest side-return or rear additions might stay cheaper. Meanwhile, multi-storey or luxury designs exceed standard price levels if advanced structural solutions or premium materials are implemented. If you add a kitchen or bathroom, factor in the extra plumbing, waterproofing, and electrical lines that increase final bills.

When gathering quotes from building contractors, ensure each quote specifies whether it includes foundation work, structural assembly, roofing, fittings, finishing, labour, overhead, and so on. Clarify if VAT—commonly 20%—is included or separate. Although magazines and renovation websites supply general figures, genuine accuracy demands multiple quotes from established trades and a thorough line-by-line comparison.

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.

Islington

Islington, often described as vibrant and cosmopolitan, is known for its Georgian squares, Victorian terraces, and modern developments intermixed around areas like Angel, Highbury, and Barnsbury. Many residents expand small ground-floor kitchens to create an open-plan living-dining area that captures more natural light—especially common in those classic Islington terraces with narrow footprints. Others attempt side-return extensions if the property includes a narrow side yard, reclaiming previously wasted space. Loft conversions are also prevalent, transforming pitched or mansard roofs into new bedrooms or studies, often in prime spots near Upper Street’s amenities.

Local contractors mention that busy roads such as Upper Street or Essex Road can complicate skip drop-offs and material deliveries, so scheduling them off-peak is important. Labour costs here can be on the higher side, and the borough features multiple conservation areas—for instance, around Canonbury or Arlington Square—adding extra scrutiny to external changes. Still, a well-planned extension can provide a huge boost in daily comfort and property value, particularly if you’re near key tube stations (e.g., Angel) or Overground links (e.g., Highbury & Islington). It’s wise to let neighbours know if you share boundary walls or if the build might affect them, minimising potential disputes.

Whether your plan is a small single-storey rear design to create a spacious kitchen-lounge or a more ambitious multi-storey overhaul, adapting it to Islington’s local character and planning guidelines will simplify approvals and result in a final aesthetic that suits the borough’s architectural style.

Getting Started

Before launching the build, choose which extension approach suits your Islington house. A single-storey rear addition might unify living and cooking zones, while a double storey design can provide both ground-floor and upper-level rooms. If you have a small, enclosed side passage typical of Islington terraces, a side-return extension can reclaim that space. Alternatively, a loft or basement might be an option if outward expansion is restricted, although basements are less frequent unless you reside in more premium streets near Highbury Fields or Barnsbury.

Robust planning early in the process often prevents mid-project turmoil. Outline a comprehensive budget, referencing labour fees and material rates, and leave a contingency for structural surprises or upscale finishes. If your design entails major structural updates, you might hire an architect or an experienced designer. Certain building firms provide a design-and-build service but typically want preliminary plans or partial planning permission to quote accurately. Many Islington homeowners consult an architect first, then gather quotes from building contractors.

Also, you should secure a contractor well before your planned start date, as reputable trades often book up quickly. Comparing multiple quotes early lets you examine cost details, investigate references, and select a builder who aligns with your vision. A seasoned contractor may refine your plan—for example, placing additional rooflights for more natural illumination or adding a discrete utility closet.

Project Management

When organising an extension, two main frameworks exist:

• Single contract (design-and-build or main contractor)
  You sign one contract with a building company that manages everything, including foundations, structural work, plumbing, electrics, roofing, and finishing. They usually subcontract specialist trades, applying around 10–15% markup. This consolidates oversight and ensures a single point of communication for the client.
• Multi-trade or split contract
  You hire each trade individually—groundworkers, carpenters, roofers, electricians, plumbers, etc. While you might bypass a main contractor’s overhead, you also take on scheduling. If one trade finishes late, subsequent tasks might face delays or increased costs. This method suits owners willing to handle daily coordination and who have adequate construction familiarity.

For large or architecturally demanding builds in Islington, many owners choose a single-contractor approach, given they may not have time for trade-by-trade management. If you do multi-trade, be ready to devote hours weekly, ensuring deliveries and tasks align seamlessly.

Do I Need Planning Permission?

Whether you need planning permission depends on the extension’s size, height, and property location. Under Permitted Development Rights, you can sometimes enlarge your home without lodging a formal application, provided you keep within certain dimensional constraints. If your proposal exceeds these allowances, you generally must file 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.

Because Islington includes numerous conservation areas—like Barnsbury, Canonbury, or Angel—some expansions that would ordinarily be PD might need planning approval. Checking with Islington Council’s planning office early clarifies if your extension meets PD or must be formally submitted.

Do I Need Planning Permission For A New Storey?

Loft conversions that modify rooflines or incorporate dormers typically require planning permission. Yet you might add a brand-new storey through permitted development if your design follows strict criteria and you file a prior approval with local authorities. Otherwise, Householder/Full Planning Permission is required. If your property meets those rules, see the bullet points below for the key 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.

Further conditions may apply when the work completes. Because many Islington terraces form uniform roofscapes, ensuring harmony with the neighbouring rooflines is typically crucial.

Do I Need Planning Permission For A New Basement?

Generally, a new basement needs planning permission, and large-scale excavation under the property is similarly likely to require planning permission due to its extent. It’s wise to consult Islington’s planning authority at the outset, gauging their expectations. Basements are inherently big projects, so even if formal planning permission may not always be mandatory, Building Regulations definitely apply to ensure structural resilience, safe exit routes, adequate ventilation, damp-proofing, and so on.

Confirm any local constraints that can override standard PD expansions. Areas around Islington—particularly near Angel or in historically sensitive squares—often have stricter measures for underground expansions. Checking council guidelines or engaging a planning specialist can secure clarity.

Although some owners in prime spots near Highbury Fields or Barnsbury occasionally build basements to gain extra living space, the cost is high due to engineering complexities and potential party-wall negotiations.

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 often detects design or stability issues before building begins, whereas a Building Notice can suffice for more modest expansions. Both routes end with building control issuing approval, confirming code adherence.

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 your Islington extension qualifies under PD, you must still meet building regulations for stable foundations, suitable insulation, damp resistance, and so on. Given many older Georgian or Victorian houses in the borough, verifying load-bearing capacity is usually vital.

DIY Contribution

Homeowners sometimes consider handling certain extension tasks personally. Painting, decorating, or landscaping can be viable DIY undertakings if you have the necessary aptitude. Doing your own demolition, to an extent, may also be feasible—provided you identify structural walls and observe safety requirements.

However, tasks including electric rewiring, gas line connections, or structural adaptations typically belong to licensed professionals. Errors can become safety hazards or lead to substantial rework. Being forthright about your skill set is essential; overshooting can stall the job. Builders may have to pause if your part isn’t completed, raising final bills. If you do want to do some DIY, seeking professional advice first can help you avoid major blunders.

In Islington, partial DIY frequently focuses on final décor or small-scale landscaping once the main structural aspects finish. Attempting advanced mechanical or structural tasks on your own can jeopardise official inspection timelines or degrade project quality.

Do I Need An Architect?

If your planned changes are straightforward, a structural engineer or building designer may be enough. But for a larger or more challenging layout, an architect can prove invaluable. Skilled architects combine aesthetic flair, functional layout, and integration of the new space with existing rooms and any external areas, such as gardens or terraces.

They can also advise whether your extension requires planning permission or fits under PD. While an architect’s fee lifts your initial spend, it often spares you from flawed designs that might need big alterations halfway through.

Islington, famous for its squares, terraced streets, and lively artistic scene, houses everything from Georgian terraces near Angel to post-war blocks in Highbury. An architect can propose blending older exteriors with a bright, modern extension—perhaps featuring foldable glass walls or partial skylights—while preserving the borough’s historic ambiance.

How Long Does It Take To Build An Extension?

Establishing a realistic timeline is vital for staying in control. A smaller single-storey rear project—especially if basic and using standard materials—could wrap up in mere weeks once ground and structural works begin, assuming it meets PD. Larger expansions, multi-room or multi-level, might run from a few months to half a year or beyond, dictated by how intricate the build is and how many trades are involved.

At times, you might opt to move out temporarily if central walls are demolished or essential utilities shut down. Even if you remain, anticipate dust, noise, and limited access to specific rooms.

Always build slack into your schedule. Bad weather can hamper exterior tasks, inspectors can request modifications, or deliveries might lag behind. Setting a sensible timescale with your contractor helps contain stress, and if you finish early, so much the better. Likewise, a financial cushion is recommended for unforeseen tasks or design changes mid-flow.

Islington experiences heavy traffic near Angel or Highbury Corner, so skip drop-offs commonly dodge peak hours. If you revise design specifics after the build launches, you risk extending completion further.

House Extensions Step By Step

While launching an extension is major, with thorough planning, trustworthy trades, and a well-considered budget, it’s entirely doable. Whether you want extra space for a new family room, to upgrade a loft into bedrooms, or even to attempt a basement, watch out for each stage and typical pitfalls.

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. Resolve any outstanding issues before final payment. Keep building control approvals, warranties, and official compliance documents for any mortgage or resale situation.

Once your extension secures its final sign-off, you’ll have a more spacious, functional residence in Islington. Whether you fashioned a bright rear living-dining zone or added a second storey, these improvements typically augment comfort and property desirability. A snagging survey catches finishing flaws—like faint cracks, uneven paint lines, or misaligned fittings—so you can remedy them. Filing building control records and warranties proves compliance with regulations, reassuring prospective buyers or lenders. That done, your newly expanded Islington home can accommodate your family’s evolving needs for years ahead.