Two-Storey Annexe Extensions for Family

What you get

This service suits you if a parent, grown-up child or carer is moving in and you want them to have their own space while staying connected to the house. You get a layout that can be self-contained or shared, the approvals your nation needs with the annexe use made clear, accessible design where needed and the build, carried out by vetted teams working under S&K.

It suits you if…

An elderly parent is moving in and needs their own space
A grown-up child needs independence but is not ready to buy
You want a ground-floor bedroom and shower room for future needs
You have a side plot wide enough for a self-contained layout

Line drawing: existing house in outline, new work in brick, blue dashed line at first-floor level.

Design points that matter

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.

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.

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.

Planning and approvals by nation

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.

Wales

In Wales, a two-storey annexe extension can use the same permitted development rules as other extensions: 4 m ground floor and 3 m first floor at the rear, or the 10.5 m, 1 m set-back and 50% width tests at the side. If you apply, the householder fee is £585, and councils may limit the annexe to use by the household.

Approval in Wales: Householder planning application: £585. Councils normally decide householder applications within 8 weeks.

Building regulations: Building regulations approval under the Welsh Approved Documents, which differ from England's in places (notably energy efficiency).

Scotland

In Scotland, a two-storey annexe extension needs to be at least 10 m from every boundary to be permitted development under Class 1B, so most need a householder application (£371, decided within two months). The building warrant covers fire safety and escape for the self-contained layout.

Approval in Scotland: Householder planning application: £371. Councils have two months to decide a local planning application.

Building standards: A building warrant from the council's building standards service before work starts, and a completion certificate at the end. Scotland uses its own Technical Handbooks.

Northern Ireland

In Northern Ireland, a two-storey annexe at the rear can be permitted development within 3 m of the original rear wall and 7 m from the rear boundary, with the usual conditions. A side annexe needs a planning application costing £347, and councils may add conditions linking its use to the main house.

Approval in Northern Ireland: Planning application for works to a house: £347. Councils aim to decide local applications within an average of 15 weeks; many take longer.

Building control: Building control approval from the local council under the Building Regulations (Northern Ireland), using the Technical Booklets.

Guide price

As a guide, a two-storey annexe extension built to the side costs £86,000–£115,500 including VAT at 20% for a 3 m × 7 m footprint on two floors (42 m² of new floor space), plus kitchenette and shower room fittings, based on West Midlands prices and our Standard spec; London and the South East are higher.

Guide prices by region
Region	Per m² of new floor	Typical project
London	£2,460–£3,300 per m²	£103,500–£138,500
South East England	£2,260–£3,030 per m²	£94,500–£127,000
East of England	£2,110–£2,830 per m²	£88,500–£119,000
South West England	£2,110–£2,830 per m²	£88,500–£119,000
West Midlands	£2,050–£2,750 per m²	£86,000–£115,500
East Midlands	£2,010–£2,700 per m²	£84,500–£113,000
North West England	£1,950–£2,610 per m²	£82,000–£109,500
Yorkshire and the Humber	£1,890–£2,530 per m²	£79,000–£106,500
North East England	£1,840–£2,480 per m²	£77,500–£104,000
Wales	£1,890–£2,530 per m²	£79,000–£106,500
Scotland	£1,930–£2,580 per m²	£81,000–£108,500
Northern Ireland	£1,800–£2,420 per m²	£76,000–£101,500

Typical project: a 3 m × 7 m footprint on two floors (42 m² of new floor space), plus kitchenette and shower room fittings, priced to your choice. Including VAT at 20%, Standard spec. Essential spec is about 8% less, Premium about 20% more. See all prices and fees or work out your own guide price.

What's included

Free site visit
Measured survey, priced in writing with the design stage
Self-contained or shared annexe layout
Accessible design options
Planning application or permitted development check
Fire safety, escape and building regulations approval
Services, heating and drainage design
The build, carried out by vetted teams working under S&K

How it works

Free site visit
We look at your house, the boundaries, access and drains, and talk through what you need the new space to do.
Design and approval
Measured survey and drawings, then planning permission or a lawful development certificate, depending on the rules where you live.
Engineering and fixed price
Structural calculations and building regulations approval, then a fixed build price in writing.
Build and sign-off
Vetted teams working under S&K build it, and we arrange the completion certificate.

Questions about two-storey annexe extensions

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.

Will an annexe have its own council tax bill?

Sometimes. The Valuation Office Agency can band a self-contained annexe separately in England and Wales, though discounts or exemptions often apply when a relative lives there. Scotland and Northern Ireland have their own systems. Check with your council before the design is fixed.

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 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.

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