Single-storey rear extensions across Castlereagh
Castlereagh homeowners can use us for the whole single-storey extension project: survey, design, planning or permitted development checks, building regulations and the build itself.
- Guide price in CastlereaghFrom £18,000 inc VAT
- PlanningNI permitted development (rear 3–4 m) or planning
- Build time10–16 weeks on site
- Postcode districtsBT1, BT2, BT4, BT5, BT6
Local to Castlereagh
Site visits are available across Castlereagh (BT1, BT2, BT4, BT5, BT6, BT7). Neighbouring towns we cover include Belfast (2 miles), Newtownabbey (6 miles), Lisburn (7 miles), Carrickfergus (10 miles).
For homes towards County Down, Newtownards is around 8 miles away. In Northern Ireland, extension projects follow the NI planning rules and council building control, which we account for from the first survey.
What is included
- Doors, windows, insulation, plastering and first fix to finish
- Planning route checked and the right approval obtained
- Walls, steel beams and the new opening into the house
- Building regulations drawings and structural calculations
- Measured survey and design
What should I budget for a single-storey extension in Castlereagh?
Prices below are for Castlereagh, using the Northern Ireland factor of ×0.86. They are guide ranges including VAT for the build only, not a quote.
Typical rates in Castlereagh: £1,500 to £2,920 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| 3 m × 4 m 12 m² | £18,000 – £21,500 | £21,000 – £27,000 | £26,500 – £35,500 |
| 4 m × 5 m 20 m² | £30,000 – £35,500 | £35,000 – £45,000 | £44,500 – £58,500 |
| 5 m × 6 m 30 m² | £45,000 – £53,000 | £52,500 – £67,500 | £67,000 – £88,000 |
Want a range for your exact size? The guide-price tool takes about a minute.
Do I need planning permission in Castlereagh?
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.
The planning position for a specific Castlereagh address depends on its history and any designations, which is why we check it at the first visit.
Building close to a public sewer needs the agreement of NI Water, which we check during design.
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.
Applications are decided by your council, which handles local planning in Northern Ireland.
Our process, step by step
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
Once the layout is agreed, we deal with the council: planning permission or written confirmation that none is needed, plus building control.
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
Work is carried out to the agreed programme, inspected by building control and signed off at the end.
Questions people ask about single-storey extensions
Who do I contract with for a single-storey extension in Castlereagh?
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.
How long does a single-storey extension take to build in Castlereagh?
On site, typically 10 to 16 weeks once approvals are in place. Before that, allow 4–12 weeks design and approvals.
Can I see a price before committing to anything?
Yes. The guide prices on this page are adjusted for Castlereagh, 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 much does a single-storey extension cost per square metre?
Our guide range is about £1,500 to £2,920 per m² including VAT, depending on specification. A standard-spec 4 m × 5 m room usually lands at £35,000 to £45,000 in Castlereagh, plus design and council fees.
Flat roof or pitched roof?
Flat roofs give more headroom inside and suit lanterns and rooflights; pitched roofs can blend better with older houses. Both meet building regulations when built properly. See our flat roof and pitched roof pages for the details.
Book a free site visit in Castlereagh
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.