Two-storey annexe extensions in Greater London

Greater London at a glance

Nation: England
Price region: London
Postcode areas: BR, CR, DA, E, EC, EN, HA, IG, KT, N, NW, RM, SE, SM, SW, TN, TW, UB, W, WC
Towns covered: 215 listed below, plus surrounding villages
Approval route: Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
Site visits: Free, no obligation

What a two-storey annexe extension involves

A two-storey annexe extension is an attached extension laid out as self-contained living space on two floors, usually with a living area and kitchenette below and a bedroom and shower room above, for a relative living with the family. It stays part of the main house rather than a separate home. Planning and council tax rules treat it differently from a separate dwelling.

Across Greater London we cover Brent (HA0), Islington (EC1V), Westminster (SW1), Bexley (DA5), Barking (E6) and Archway (N6), plus the smaller places around them.

Guide price in London

Expect a two-storey annexe extension in Greater London to land somewhere around £103,500–£138,500 (plus kitchenette and shower room fittings, priced to your choice) for a 3 m × 7 m footprint on two floors (42 m² of new floor space). Our London guide rate is £2,460–£3,300 per m², including VAT. We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.

Spec	Per m²	Typical project
Essential	£2,260–£3,040 per m²	£95,000–£127,500
Standard	£2,460–£3,300 per m²	£103,500–£138,500
Premium	£2,950–£3,960 per m²	£124,000–£166,500

Rules in England

In England, an annexe on two floors is assessed like any two-storey extension: at the rear it can be permitted development if it goes no more than 3 m beyond the original rear wall and stays 7 m from the rear boundary, but at the side it needs planning permission, costing £548 (or £575 for applications made from 8 December 2026). Councils often add a condition that the annexe stays ancillary to the main house and is not let separately.

Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.

Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.

The Party Wall etc. Act 1996 applies, so notices may be needed for work on or near a shared wall or boundary.

Getting the design right

Annexe, not a separate house

To stay an annexe, the space should be used by members of the household and stay linked to the main house, usually with an internal door and shared address, garden and services. Designing it as a fully separate home can mean the council treats it as a new dwelling.

Services and metering

An annexe usually shares the main house's water, gas and electricity, with a separate circuit or sub-meter if you want to split costs. We plan heating, hot water and drainage so the annexe works well without needing new supplies.

How we work in Greater London

Look at the house
We start in Greater London with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Plans, then approval
Measured survey, design, then the right approval route for your house. We explain each step before we take it.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.

Towns we cover in Greater London

Two-storey annexe extensions in Greater London: questions

How much does a two-storey annexe extension cost in Greater London?

In London our guide is £2,460–£3,300 per m² including VAT, so about £103,500–£138,500 (plus kitchenette and shower room fittings, priced to your choice) for a 3 m × 7 m footprint on two floors (42 m² of new floor space). Essential and Premium specs move that by roughly 8% down or 20% up.

Does a two-storey annexe need planning permission?

It depends on where it goes and your nation. In England, a rear annexe extension can be permitted development within the 3 m and 7 m limits, but a side one always needs planning permission. If the annexe could work as a separate home, the council may treat it as a new dwelling, which needs full planning permission.

Can I rent out an annexe later?

Not always. Many annexe permissions include a condition that it is only used by members of the household, so renting it out may need a fresh planning application. If you think you might want to let it, tell us at the start so we can explain the options.

Can an annexe have its own front door?

It can, but a separate front door, kitchen and address together make it look more like a separate home, which can change how the council treats it for planning. Many annexes have their own door to the garden or side and an internal door to the main house. We explain how each choice is likely to be viewed before the design is fixed.

Will I need planning permission in Greater London?

Greater London is in England. Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.

Neighbouring areas

All extension services in Greater London · About two-storey annexe extensions