What is a double-storey extension?
A double-storey extension (also called a two-storey extension) adds rooms on both the ground and first floor in one build. It typically gives a larger kitchen or living space downstairs and an extra bedroom or bathroom above.
How much does a double-storey extension cost in Highgate?
In Highgate, a double-storey extension typically costs £2,150–£3,250 per m² of floor area (both floors), including VAT at 20% (standard rate). For a typical 36 m² project that is roughly £77,500–£117,000. The guide for Highgate reflects typical costs in London, roughly 30% above the UK-wide figure. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (25 m²) | £54,000–£81,000 |
| Typical project (36 m²) | £77,500–£117,000 |
| Larger project (50 m²) | £107,500–£162,500 |
| Rate per m² | £2,150–£3,250 |
The main things that change the cost:
- Scaffolding and access to the rear
- Bathrooms or en-suites on the first floor
- Roof design and how it joins the existing roof
- Total floor area across both floors
A guide range is only a starting point: the guide price tool gives an instant figure for your size, and a free survey turns it into a fixed quote.
Do you need planning permission for a double-storey extension in Highgate?
Before anything is built in Highgate, we confirm which approvals apply in England. In England an extension of more than one storey can only be permitted development at the rear, no more than 3 metres deep and at least 7 metres from the rear boundary, with matching materials and any upper side windows obscure-glazed. Most double-storey extensions therefore go through a householder planning application.
Where work involves a shared wall, building on the boundary, or digging foundations within 3 metres of a neighbour’s building and deeper than its foundations (or within 6 metres for deeper work), the Party Wall etc. Act 1996 applies and notices must be served before work starts.
At the survey we check your house’s planning history and any restrictions, and tell you which route applies.
What we handle
On a typical double-storey extension we handle:
- Electrics, heating, plumbing and plastering
- Structural engineer’s calculations
- Brick or block walls, floors and a roof tied into the house
- Building control sign-off
- Foundations, drainage and scaffolding
- Design drawings and planning application
How long does it take?
Build time is typically 14 to 20 weeks on site, after planning and building control approval. Before that, surveys, drawings and approvals usually take 3 to 4 months, longer if the council asks for changes.
Building in Highgate
Many London boroughs have conservation areas and detailed design guides, so early design advice saves time at the planning stage.
Projects in Highgate (N6) are surveyed in person before we quote, so the price reflects your actual property.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Design and fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 03
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about double-storey extensions in Highgate
Can I live at home during the work?
Most families stay put. The shell is built first and the house is opened up late in the job, so disruption inside is limited to a few weeks.
How close can it be to my neighbour?
Councils look at loss of light and outlook for neighbours. Many apply a 45-degree guideline from the nearest neighbouring window. We design to the council’s published guidance to give the application the best chance.
How much does a double-storey extension cost in Highgate?
In Highgate, a double-storey extension typically costs £2,150–£3,250 per m² of floor area (both floors), including VAT at 20% (standard rate). A typical 36 m² project comes to roughly £77,500–£117,000. Your fixed price depends on the survey and drawings.
Who approves a double-storey extension in Highgate?
Planning matters in Highgate go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
What drawings do I need?
Planning drawings for the application, then more detailed building regulations drawings and structural calculations for building control. We prepare both.