House Extensions in North London

(Side returns, rear extensions, double-storey, wraparounds, and more)

Why extend your home?

Moving is disruptive. If you’ve built a life in Hampstead, Finchley, or Barnet, the thought of leaving neighbours, schools, and routines behind can be daunting. Yet houses don’t always keep pace with the families who live in them. Kitchens become bottlenecks, bedrooms feel cramped, and storage mysteriously evaporates as children grow older.

That’s why so many North Londoners turn to extensions. A house extension is more than extra square footage – it’s about unlocking the full potential of your home and making everyday life more enjoyable.

We’ve seen extensions completely transform the way people live:

  • A family in Camden who turned a dark galley kitchen into the heart of their home with a side return.
  • A Finchley couple who added two bedrooms and a larger lounge by building a double-storey extension.
  • A Barnet homeowner who created a seamless indoor-outdoor lifestyle with a wraparound extension and glazed corner.

In short, extensions give you room to breathe – and often add significant value to your property.

Types of house extensions

Every house is different, and so are the extension options. Here’s a guide to the main types we design in North London:

Rear extensions

  • Extend out into the garden, often from the kitchen or dining room.
  • Ideal for creating open-plan family spaces with doors onto the garden.
  • Common in Victorian terraces and 1930s semis.
  • Many rear extensions fall under permitted development rights.

Side return extensions

  • Perfect for terraced houses with narrow side alleys.
  • Often just 1–2 metres wide, but they make a huge difference to light and flow.
  • Popular in Hampstead and Camden where plots are tight.
  • Frequently combined with rooflights or glazed walls.

Double-storey extensions

  • Add living space downstairs and extra bedrooms or bathrooms upstairs.
  • Require planning permission but can significantly increase value.
  • Well-suited to family homes in Finchley and Barnet.

Wraparound extensions

  • Combine rear and side returns for maximum impact.
  • Turn a dark and fragmented ground floor into a light-filled, spacious hub.
  • Works best for detached or semi-detached homes.

Loft and extension combos

  • Many homeowners extend out and up at the same time.
  • Creates a balanced upgrade, avoiding the “lopsided” feel of a single extension.
  • Cost-effective if you’re already carrying out major works.

Basement extensions

  • More complex but sometimes the only option in conservation areas or dense locations.
  • Add gyms, playrooms, wine cellars, or even cinemas.
  • Seen more in Hampstead and Highgate where plots are constrained.

Planning permission and permitted development

One of the biggest questions homeowners ask is: Do I need planning permission?

The answer depends on your property type, borough, and conservation status.

Permitted development rights

  • Many rear and side extensions qualify under permitted development (PD).
  • PD allows certain works without a full planning application, provided they meet strict size and design criteria.
  • For example:
    • Single-storey rear extensions up to 3 metres (terraced houses) or 4 metres (detached houses).
    • Larger rear extensions (up to 6–8 metres) may require a prior approval process.
    • Side extensions must be single-storey, less than half the width of the house, and under 4 metres high.

When full planning permission is required

  • Double-storey extensions.
  • Wraparound extensions.
  • Any works in conservation areas (e.g. Hampstead Garden Suburb).
  • Listed buildings, where listed building consent is also needed.
  • Flats and maisonettes (PD rights don’t apply).

Local borough approaches

  • Camden: Often strict on heritage and conservation, especially in Hampstead and Highgate.
  • Barnet: More flexible for suburban semis and detached homes.
  • Brent: Practical in residential areas but stricter near high streets.
  • Westminster: Very restrictive, particularly in listed or heritage streets.

Because DOR Architects work across these boroughs, we know the quirks of each planning department – and how to present schemes in ways that maximise approval chances.

Costs of extensions in North London

Costs are always the elephant in the room. While every project is unique, here are ballpark figures:

  • Single-storey side or rear extension: £2,500–£3,500 per m²
  • Double-storey extension: £3,000–£4,000 per m²
  • Wraparound extension: £3,000–£3,800 per m²
  • Basement extension: £4,500+ per m²

Example scenarios

  • Side return in Camden: A 15m² side return at £3,000/m² = £45,000 build cost, plus £10–15k for design, planning, and approvals.
  • Double-storey in Barnet: A 40m² two-storey extension at £3,200/m² = £128,000 build cost, plus £20k+ for design and technical drawings.
  • Basement in Hampstead: A 50m² basement at £4,800/m² = £240,000 build cost, plus specialist waterproofing and structural engineering fees.

These numbers can rise with high-end finishes (think bespoke kitchens or imported stone), but a well-designed extension typically adds more value to your property than it costs to build.

Lifestyle benefits of extensions

Extensions aren’t just about bricks and mortar. They reshape the way you live:

  • Family life: Larger kitchens and open-plan spaces become social hubs.
  • Working from home: Garden rooms and loft conversions make perfect offices.
  • Multi-generational living: Double-storey extensions allow space for grandparents or teenagers.
  • Entertaining: Wraparound designs connect inside and outside, perfect for gatherings.
  • Resale value: Buyers love light, flexible homes – extensions often make properties far more attractive.

Why choose DOR Architects for your extension?

  • Design clarity: We use 3D modelling so you can visualise every option before committing.
  • Cost control: Our background in construction means fewer surprises on site.
  • Planning expertise: We’ve secured approvals across Camden, Barnet, Brent, and Westminster.
  • Interiors included: We don’t just add space – we reimagine the way your home flows.
  • Trusted network: Access to experienced engineers, contractors, and specialists.

Our process for homeowners

  1. Initial Consultation – Understanding your goals, budget, and property constraints.
  2. Concept Design – Exploring layouts, light, and materials using 3D models.
  3. Planning or Permitted Development – Identifying the smoothest approval path.
  4. Technical Design – Detailed drawings and coordination with engineers.
  5. Tendering – Helping you select reliable contractors.
  6. On-Site Support – Making sure what’s built matches the design intent.

Case studies and local insights

  • Camden terrace: A side return added just 1.8 metres but completely transformed the kitchen, with skylights bringing light into the centre of the house.
  • Barnet semi-detached: A double-storey rear extension created a family lounge and two new bedrooms, approved on the first application.
  • Finchley detached home: A wraparound extension with full-height glazing turned a tired 1930s house into a contemporary home.

FAQs

Do I need a party wall agreement for my extension?
Yes, if your extension is close to or affects a shared wall. We can guide you through the process.

Can I live in the house during construction?
For smaller extensions, often yes. For major works, it may be better to move out temporarily.

What’s the timeline for a house extension?

  • Design and planning: 3–4 months
  • Technical drawings: 1–2 months
  • Build: 4–8 months depending on scale

Will an extension always add value?
Almost always, provided it’s well-designed and matches local market demand. Poorly designed extensions can have the opposite effect.

Do you handle listed building extensions?
Yes. We’ve worked on listed homes in Hampstead and Highgate, securing both planning and listed building consent.

Can I build a basement under permitted development?
No – basements always require full planning approval.

Do you work outside North London?
Our focus is North London, but we do occasionally take on projects further afield.

Next steps

If you’re a North London homeowner considering an extension, the first step is a conversation. We’ll help you understand what’s possible, what it might cost, and how the process works.

Book a free homeowner consultation with DOR Architects – and see how your house could work harder for you.

Disclaimer

This guide is for general information only and does not constitute legal or professional advice. Always consult with a qualified architect or planning consultant for your specific circumstances.