Two-storey annexe extensions in County Londonderry

County Londonderry at a glance

Nation: Northern Ireland
Price region: Northern Ireland
Postcode areas: BT
Towns covered: 11 listed below, plus surrounding villages
Approval route: Planning permission is needed: permitted development side extensions in Northern Ireland can't be more than 4 m high, which rules out two storeys.
Site visits: Free, no obligation

What a two-storey annexe extension involves

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.

The main places we list in County Londonderry are Derry (BT48), Coleraine (BT51), Limavady (BT49), Magherafelt (BT45), Portstewart (BT55) and Portrush (BT56). We cover the villages in between too.

Guide price in Northern Ireland

For budgeting in County Londonderry, allow around £76,000–£101,500 (plus kitchenette and shower room fittings, priced to your choice) for a two-storey annexe extension with a 3 m × 7 m footprint on two floors (42 m² of new floor space). That's based on £1,800–£2,420 per m² including VAT for Northern Ireland. 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	£1,660–£2,230 per m²	£69,500–£93,500
Standard	£1,800–£2,420 per m²	£76,000–£101,500
Premium	£2,160–£2,900 per m²	£91,000–£122,000

Rules in 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.

There is no Party Wall Act in Northern Ireland. Shared walls and boundaries are a matter of title and common law, so we agree access and record conditions with neighbours before work starts.

Getting the design right

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.

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.

How we work in County Londonderry

Measure and listen
A visit to County Londonderry to understand how you live in the house now and what the extra rooms need to do, plus a first look at the structure.
Plans, then approval
Measured survey, design, then the right approval route for your house. We explain each step before we take it.
Structure and building control
A structural engineer sizes the foundations and steels, and we get building regulations approval before work starts.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.

Towns we cover in County Londonderry

Two-storey annexe extensions in County Londonderry: questions

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

In Northern Ireland our guide is £1,800–£2,420 per m² including VAT, so about £76,000–£101,500 (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.

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.

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 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.

Will I need planning permission in County Londonderry?

County Londonderry is in Northern Ireland. Planning permission is needed: permitted development side extensions in Northern Ireland can't be more than 4 m high, which rules out two storeys.

Neighbouring areas

All extension services in County Londonderry · About two-storey annexe extensions