Two-storey annexe extensions in Lancashire

Lancashire at a glance

Nation: England
Price region: North West England
Postcode areas: BB, FY, L, LA, OL, PR, WN
Towns covered: 30 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.

Lancashire towns we list: Preston (PR1), Burnley (BB10), Blackburn (BB1), Blackpool (FY1), Morecambe (LA4) and Lancaster (LA1). Every other address in Lancashire is covered as well.

Guide price in North West England

Using our North West England rates, a two-storey annexe extension with a 3 m × 7 m footprint on two floors (42 m² of new floor space) comes to about £82,000–£109,500 (plus kitchenette and shower room fittings, priced to your choice), including VAT. Bigger or more glazed designs cost more per m². Steelwork for wide openings is the item most likely to move the figure; we'll know once the engineer has designed it.

Spec	Per m²	Typical project
Essential	£1,790–£2,400 per m²	£75,500–£101,000
Standard	£1,950–£2,610 per m²	£82,000–£109,500
Premium	£2,340–£3,130 per m²	£98,000–£131,500

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

Ground-floor living for the future

Many annexes are planned so the occupant could live on the ground floor if stairs become difficult. A ground-floor bedroom space, a level-access shower and wider doorways cost little at the design stage and are expensive to add later.

Fire separation and escape

A kitchenette in an annexe and a bedroom above need safe escape and suitable separation from the main house. Building control checks the escape windows, smoke alarms and the door between the two parts.

How we work in Lancashire

Start at your house
We come to your home in Lancashire, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
Get it approved
Once you're happy with the design we submit it to the council for Lancashire and deal with any questions from the planning officer.
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.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.

Towns we cover in Lancashire

Two-storey annexe extensions in Lancashire: questions

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

In North West England our guide is £1,950–£2,610 per m² including VAT, so about £82,000–£109,500 (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 an annexe be designed for someone with limited mobility?

Yes. We can plan a ground-floor bedroom space, a level-access shower, wider doorways, lever handles and space for a stairlift later. These features are much cheaper to build in at the start than to add afterwards, and they keep the annexe useful as needs change.

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 Lancashire?

Lancashire 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 Lancashire · About two-storey annexe extensions