House Extension Costs in North London (2026)
Last updated: June 2026 · Figures verified against live North London quotes, the April 2026 government fee schedule and current council planning records.
Quick answer: A single-storey rear extension in North London costs £45,000–£90,000 to build in 2026 (£2,800–£4,200 per m²), excluding VAT, professional fees and kitchen fit-out. Premium areas like Highgate and Hampstead run £3,500–£5,000+ per m². A typical 20m² kitchen extension lands at £75,000–£110,000 all-in.
If you're planning an extension in North London, the honest answer to "what will it cost?" is: more than the national average, and it depends heavily on your postcode, your property, and your spec. North London's housing stock — Victorian and Edwardian terraces, 1930s semis, period conservation-area homes — and London labour rates push prices above the figures you'll see quoted for the rest of the UK. This guide gives real 2026 ranges for the area we cover (Enfield, Barnet, Southgate, Winchmore Hill, Cockfosters, Palmers Green, Highgate, Muswell Hill, Potters Bar and the surrounding towns), what those prices include, and the local factors that move them.
Quick reference: North London extension costs, 2026
These are realistic all-in build ranges for North London (labour and materials, to a good standard finish) — excluding VAT and professional fees, which we break down further below.
| Extension type | Typical size | North London cost (2026) |
|---|---|---|
| Side return extension | 8–12 m² | £35,000 – £65,000 |
| Single storey rear extension | 15–20 m² | £45,000 – £90,000 |
| Kitchen extension (rear, incl. mid-range kitchen) | 18–25 m² | £55,000 – £110,000 |
| Wrap-around extension | 20–30 m² | £70,000 – £140,000 |
| Double storey / two-storey extension | — | £75,000 – £160,000 |
| Loft conversion (dormer) | — | £45,000 – £75,000 |
| Loft conversion (hip-to-gable + dormer) | — | £55,000 – £90,000 |
| Garage conversion | — | £18,000 – £35,000 |
| Basement conversion / dig-out | — | £100,000 – £250,000+ |
Every project is different — these are guide figures to set your expectations, not a quote. We give an itemised, fixed quote after a free site visit.
Cost per square metre in North London
The cleanest way to sanity-check a quote is per square metre. As a rule of thumb for 2026:
- National UK average: £1,500 – £2,500 per m² for the build.
- North London: £2,800 – £4,200 per m² for the build, excluding VAT and excluding kitchen/bathroom fit-out.
So a 20 m² single storey rear extension in Southgate or Winchmore Hill typically lands around £60,000–£80,000 for the build alone, before you add a kitchen, VAT (where it applies) and fees. North London sits 20–40% above the national figure for three reasons: London labour and trades cost more, period properties need more careful (slower) work to match existing brick and detail, and access on tight terraced streets adds time and logistics.
Costs by extension size
Size is how most people actually think about their project — "what would a 3m by 5m cost?" is one of the most-searched extension questions in the UK. These are North London build costs at 2026 rates (£2,800–£4,200/m², excluding VAT, fees and kitchen units), with the all-in range adding typical professional fees and VAT:
| Size | Footprint | Build cost | Realistic all-in | What it gets you |
|---|---|---|---|---|
| 3m × 3m | 9m² | £25,000 – £38,000 | £36,000 – £53,000 | Utility + WC, or a dining nook |
| 3m × 4m | 12m² | £34,000 – £50,000 | £47,000 – £69,000 | Compact kitchen-diner widening |
| 3m × 5m | 15m² | £42,000 – £63,000 | £57,000 – £85,000 | Proper kitchen-diner — the UK's most-searched size |
| 4m × 4m | 16m² | £45,000 – £67,000 | £61,000 – £91,000 | Square family kitchen with island |
| 4m × 5m | 20m² | £56,000 – £84,000 | £75,000 – £110,000 | Full-width kitchen-living space |
| 4m × 6m | 24m² | £67,000 – £100,000 | £89,000 – £130,000 | Open-plan kitchen, dining and snug |
| 25m²+ | 25–35m² | £70,000 – £147,000 | £93,000 – £185,000 | Wrap-around territory — full ground-floor rework |
Depth drives planning as well as price: up to 3m deep (4m detached) is usually permitted development; 3–6m (8m detached) uses the £249 prior-approval route; beyond that you're into a full £548 application. The Extension Builder prices your exact size and gives the planning route in 60 seconds.
What the price does — and doesn't — include
This is where most North London homeowners get caught out. A headline build price usually covers groundwork, structure, walls, roof, glazing, plastering and a basic finish. It usually does not include:
- The kitchen itself — units, worktops and appliances are typically £8,000–£30,000 on top for a kitchen extension, depending on spec.
- VAT — most residential extension work is standard-rated at 20%. Always check whether a quote is inclusive.
- Professional fees — design, planning, structural engineering and building control (see below).
- Bespoke extras — roof lanterns, large structural sliding/bifold doors, underfloor heating, high-end flooring and landscaping.
When you compare two quotes, compare what's in them — a cheaper number is often cheaper because it's leaving more out.
Seven things that move the price in North London
- Period housing stock. Victorian and Edwardian terraces (common across Winchmore Hill, Crouch End, Highgate and Palmers Green) need matching London stock brick, careful structural openings into solid walls, and detailing that takes longer than a modern build.
- Conservation areas. Monken Hadley, parts of Highgate, Winchmore Hill and Hadley Wood carry conservation-area controls that can require higher-spec materials and more design work — and remove some permitted development rights.
- Party Wall agreements. On terraced and semi-detached homes (most of the area), you'll usually need a Party Wall agreement with neighbours. Budget £1,000–£2,500+ per neighbouring owner if surveyors are appointed.
- Access and logistics. Narrow terraced streets, restricted parking and skip/scaffold licences add cost on tight North London sites compared with a detached home with side access.
- Ground conditions. Clay soils across much of North London affect foundation depth; basements and dig-outs are sensitive to the water table and neighbouring structures.
- Specification. The single biggest swing. The same footprint can vary 40%+ between a practical family finish and a high-end scheme with structural glazing, a feature kitchen and underfloor heating — which is common in EN4, N6 and N10.
- Structural complexity. Removing load-bearing walls for open-plan living, steel beams, and large openings all add engineering and build cost.
Costs by area
Affluent North London postcodes tend toward higher specs (and therefore higher total project values), even for the same footprint:
- Cockfosters & Hadley Wood (EN4): larger plots and higher-end finishes; rear and wrap-around extensions frequently £90k–£160k+.
- Southgate & Oakwood (N14): strong period and 1930s stock; single storey and kitchen extensions commonly £55k–£100k.
- Winchmore Hill & Palmers Green (N21, N13): Edwardian terraces and semis; side return and rear kitchen extensions £45k–£95k.
- Highgate & Muswell Hill (N6, N10): period, often conservation-controlled; expect higher material/design spend.
- Enfield (EN1–EN3): the widest mix; practical family extensions from the mid-£40ks upward.
- Barnet (EN5/EN4) & Potters Bar (EN6): semis and detached with side access; double storey and loft projects well represented.
Professional fees — budget 10–18% on top
Beyond the build, a properly run project includes:
- Design & drawings: typically 8–15% of build cost for a full design-and-build service.
- Planning application: local authority fee plus drawings/documents where a full application is needed (many extensions qualify under permitted development — see our planning guide).
- Structural engineer: ~£600–£1,500 for calculations and beam design.
- Building control: local authority or approved inspector fees for sign-off.
- Party Wall surveyor: where required (see above).
Do you need planning permission? (It affects cost and timeline)
Many single storey rear extensions in North London are built under permitted development — no full planning application — which saves time and fees. But conservation areas, listed buildings, flats and larger schemes need a full application, and each borough (Enfield, Barnet, Haringey, Hertsmere for Potters Bar) applies the rules slightly differently. See our council-by-council planning guides before you budget.
How to get an accurate figure
Online ranges only get you so far. The price of your extension depends on your property, your ground, your spec and your borough. We offer a free site visit and a fixed, itemised quote across North London — no obligation. Get a free quote →
Frequently asked questions
How much does a single storey extension cost in North London in 2026? Typically £45,000–£90,000 for the build (around £2,800–£4,200 per m²), excluding VAT, the kitchen and fees. A 20 m² rear extension in Southgate or Enfield usually lands in the £60k–£80k build range.
Why are North London extensions more expensive than the national average? London labour rates, period properties that need careful matching work, tight-site access on terraced streets, and higher specifications all push North London 20–40% above the UK average.
Does a house extension add value in North London? In most of the area a well-designed extension adds value, and a larger kitchen-diner or extra bedroom is among the most sought-after improvements — but in high-value postcodes always weigh spend against the local ceiling price.
Is VAT included in extension quotes? Usually not — most residential extension work is standard-rated at 20%. Always confirm whether a quote is VAT-inclusive.
Do I need a Party Wall agreement? On most North London terraced and semi-detached homes, yes — budget £1,000–£2,500+ per affected neighbour if surveyors are appointed.