Annexe extensions in Derry/Londonderry: design, approvals and build
We design and build annexe extensions for houses in Derry/Londonderry, with a written price once the survey and design are done and one point of contact throughout.
- Guide price in Derry/LondonderryFrom £47,000 inc VAT
- PlanningUsually needs planning permission
- Build time16–24 weeks on site
- Postcode districtsBT48
When an annexe extension makes sense
- Multi-generational families
- Homes with a large side or rear garden
- Relatives who need support close by
Accessibility is cheaper to design in than to retrofit. Level access, a 900 mm door width, a level-access shower and space to turn a wheelchair can all be planned into the footprint for little extra cost.
Will the council need to approve it?
In Northern Ireland the Planning (General Permitted Development) Order 2015 lets some single-storey rear extensions go ahead without planning permission, up to 3 m on a semi-detached or terraced house and 4 m on a detached house, within height and boundary limits. Larger, side and two-storey extensions normally need planning permission from the council, and building control approval is separate.
Before any drawing is finalised we check whether the house is listed, in a conservation area or subject to an Article 4 direction.
Northern Ireland has no Party Wall Act. Where work is on or close to a shared boundary, we agree access and protection with your neighbour in writing before work starts.
Building close to a public sewer needs the agreement of NI Water, which we check during design.
Applications are decided by your council, which handles local planning in Northern Ireland.
Extensions in and around Derry/Londonderry
Postcode districts we cover around Derry/Londonderry include BT48. Nearby, we also take on projects in Limavady (15 miles), Coleraine (27 miles), Magherafelt (31 miles).
Just over the County Tyrone border, Strabane is about 13 miles away. In Northern Ireland, extension projects follow the NI planning rules and council building control, which we account for from the first survey.
How much does an annexe extension cost in Derry/Londonderry?
Labour and material costs vary across the UK, so for Derry/Londonderry we use our Northern Ireland factor (×0.86). The ranges include VAT and exclude design, structural and council fees.
Typical rates in Derry/Londonderry: £1,720 to £3,270 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| Studio annexe 25 m² | £47,000 – £59,500 | £51,500 – £64,500 | £64,500 – £82,000 |
| One-bedroom annexe 35 m² | £60,000 – £75,500 | £72,000 – £90,500 | £90,000 – £114,500 |
| Larger annexe 45 m² | £77,000 – £97,000 | £92,500 – £116,500 | £116,000 – £147,500 |
For a figure based on your own dimensions, use our guide-price tool.
What happens next
Site visits are free and there is no obligation. Where drawings are needed, the design stage is priced in writing before it starts.
Free site visit
It starts with a visit to your house to measure, check access and talk through ideas and budget.
Design and approvals
We draw the design, agree it with you and handle planning or permitted development checks and building regulations.
Fixed written price
The price is fixed in writing once the design is settled, with a clear programme and payment stages.
Build and sign-off
We build it with one project manager, book the building control inspections and hand over the completion certificate.
Annexe extension questions answered
Who do I contract with for an annexe extension in Derry/Londonderry?
Your contract is with S&K Property Investments and Improvement Ltd, which designs and manages the project and the build teams who carry it out.
Can I see a price before committing to anything?
Yes. The guide prices on this page are adjusted for Derry/Londonderry, and the guide-price tool gives a range for your own size. After the survey you get a written price before anything is agreed.
How long does an annexe extension take to build in Derry/Londonderry?
On site, typically 16 to 24 weeks once approvals are in place. Before that, allow 10–16 weeks design and approvals.
How much does an annexe extension cost?
Our guide range is about £1,720 to £3,270 per m² including VAT. A one-bedroom annexe of about 35 m² is typically £72,000 to £90,500 at standard spec in Derry/Londonderry.
Can the annexe have its own front door?
Yes, many do, but it should still connect to the main house to stay clearly part of it.
Book a free site visit in Derry/Londonderry
We will measure up, check the planning position and give you honest guide figures.
- Free, no-obligation site visit
- Planning route checked before you spend on drawings
- Written price once the design is agreed
- Building control sign-off at the end
Prefer to talk? Call 0800 088 6341 or .
Book a free site visit
Tell us a little about the project and we will arrange a time.