A double-storey extension adds two floors of new space to your house in one build, typically a larger kitchen or living room downstairs with an extra bedroom, bathroom or en-suite above, sharing one set of foundations and one roof.
Whatever type of house you own in East Barnet, we start by looking at how a double-storey extension would fit it rather than offering a standard package. We cover EN4, EN5, N12 and N14 and neighbouring places such as Hadley Wood, Barnet and Enfield Town. One named person looks after you from survey to handover, and nothing is booked until you hold our figure in writing, fixed for the work described.
- Guide price
- £78,000–£156,000 inc VAT
- Time on site
- 14–22 weeks on site
- Postcodes
- EN4, EN5, N12, N14 and N20
- Planning rules
- England
- Local area
- Greater London
- Survey
- Free, with a written quote
What should you budget for a double-storey extension in East Barnet?
Here is how the guide price for a double-storey extension breaks down in East Barnet. We start from national figures and adjust for London, which comes out about 30% above the national guide. The resulting range, VAT included, is £78,000–£156,000, and a survey, at no cost to you, firms it up.
| Type of job | What it usually involves | Guide in East Barnet |
|---|---|---|
| Small (15–20m² total) | A compact rear or side extension adding a small room on each floor. | £52,000–£84,000 |
| Typical (30–40m² total) | A larger kitchen or living room below with a double bedroom or en-suite above. | £78,000–£156,000 |
| Large (50m² plus total) | Wide or deep extensions, often with a new bathroom, steelwork and high-spec glazing. | £130,000–£234,000 |
Expect these to shape the final quote:
- Combined floor area across both storeys
- How the new roof joins the existing roof
- Foundation depth, ground conditions and drains to divert
- Scaffolding duration, access and the level of finishes
What’s included?
- Insulated cavity walls with brick or render to match the house
- First-floor joists, stud walls and new openings upstairs
- Roof structure tied into the existing roof, tiled to match
- Scaffolding for the full build, erected and inspected
- Electrics, plumbing and heating by qualified trades, with certificates
- Building control inspections and completion certificate
Local housing and a double-storey extension
London's housing is dominated by Victorian and Edwardian terraces, often in yellow London stock brick, with Georgian terraces in central districts and mansion blocks across many inner areas. Outer boroughs have large belts of interwar semis, and there are extensive post-war council estates. Many houses have been split into flats, and conservation areas are widespread.
Terraces suit side-return extensions and rear dormer loft conversions; interwar semis commonly take hip-to-gable lofts. Shared party walls, restricted parking and conservation rules often shape the plans and the programme.
Whatever era your East Barnet home dates from, we plan a double-storey extension around how it is actually built rather than a one-size-fits-all specification.
Planning and building rules in East Barnet
England, Wales, Scotland and Northern Ireland each handle planning a little differently. East Barnet comes under England, covered below, and we raise any questions with the council before your quote is finalised.
In England, a two-storey rear extension can only be permitted development if it is no more than 3 m deep, at least 7 m from the rear boundary and finished to match the house. Most double-storey and all two-storey side extensions need full planning permission.
Building Regulations approval is needed, with structural calculations for beams, foundations and the roof. The Party Wall etc. Act 1996 often applies on semi-detached and terraced houses.
Rules change and every property is different, so we check the planning history and constraints for your address before we quote.
The four stages
We look at the job
We arrange a free site survey on a date convenient to you. We measure up, look at the existing structure and access, and discuss your plans for a double-storey extension so the price reflects your home.
Written quote
We turn the survey notes into a written quote. The price is fixed for the specification we agree, and the document sets out materials, scope and payment stages in plain language.
Getting ready
We handle the paperwork side: checking whether planning permission or building control approval is needed, submitting applications where they are, and scheduling the trades and materials around your dates.
Finish and handover
The work is carried out to the agreed specification, with floors and furniture protected and the site kept tidy. At the end we clean up, walk through the finished job with you and hand over any certificates.
Why homeowners choose us
Frequently asked questions
How much does a double-storey extension cost?
A typical double-storey extension of 30–40m² across both floors costs £78,000–£156,000, built to a plastered finish. As a rough guide, allow around £1,400–£2,600 per square metre plus fixed costs for groundworks, scaffolding and fees. The second storey usually costs less per square metre than the first, because foundations and roof are shared. Bathrooms upstairs and a complex roof add most. We confirm a fixed price after the survey.
Which postcodes in East Barnet do you cover?
We cover EN4, EN5, N12 and N14, along with the rest of London. If your postcode is not listed, get in touch anyway: our coverage is UK-wide, and we can usually arrange a survey wherever you live. Enter your postcode in the guide-price tool or contact form and we will confirm.
Will the extension affect my neighbours?
A double-storey extension can affect neighbours' light, outlook and privacy, which is why planning departments look closely at height, depth and window positions. Side windows facing neighbours often need obscure glass. Work near a shared wall may also need party wall notices; the Party Wall etc. Act 1996 applies in England and Wales only. We talk through these points early so the design is realistic.
Who do I deal with during the job?
One point of contact manages your project from survey to handover. They schedule the trades working under our contract, keep you updated on progress, and are the person to call with any question. You don't need to coordinate builders, electricians or decorators separately, because that is part of what we do.
Can we live at home while it is built?
Most families stay at home during a double-storey extension. The new structure is built outside first, and we only break through into the existing rooms near the end, usually one floor at a time. Upstairs, this may mean a bedroom is out of use for a week or two. We fit dust screens, protect floors and stairs, and plan any time without water or power in advance.
Near East Barnet
Our coverage in East Barnet includes EN4, EN5, N12 and N14. We also travel to Hadley Wood, Barnet and Enfield Town, so neighbouring addresses are looked after on exactly the same terms as those in town.