What is a side extension?
A side extension builds into the space beside a semi-detached or detached house, often over a driveway or side passage. It can be single-storey, for a utility room, downstairs toilet or study, or two-storey to add a bedroom above.
How much does a side extension cost in Lisburn?
In Lisburn, a side extension typically costs £1,450–£2,300 per m² of floor area, including VAT at 20% (standard rate). For a typical 28 m² project that is roughly £40,500–£64,500. The guide for Lisburn reflects typical costs in Northern Ireland, roughly 14% below the UK-wide figure. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (20 m²) | £29,000–£46,000 |
| Typical project (28 m²) | £40,500–£64,500 |
| Larger project (39 m²) | £56,500–£89,500 |
| Rate per m² | £1,450–£2,300 |
What moves the price most:
- Roof design and tile matching
- Boundary walls and access for materials
- Single or two storeys
- Steel work where the side wall is opened
Your exact price depends on the survey and drawings. The guide price tool gives a quick range in the meantime.
Do you need planning permission for a side extension in Lisburn?
Before anything is built in Lisburn, we confirm which approvals apply in Northern Ireland. In Northern Ireland a single-storey side extension can be permitted development if it is no more than 4 metres high, no wider than half the original house and not beside a wall facing a road. Side extensions of more than one storey need planning permission.
Northern Ireland has no Party Wall Act. Work on shared walls relies on agreement with the neighbour and common law, so we agree the arrangements in writing before work starts.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
The work we manage on a side extension:
- Walls, roof and windows to match the house
- Building control completion
- Planning drawings and application
- Structural calculations
- Survey of the boundary, drains and access
- Opening into the existing house
How long does it take?
The build itself usually takes 10 to 16 weeks on site depending on size and storeys. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in Lisburn
Northern Ireland has many detached and semi-detached homes on generous plots, which suits single-storey rear extensions and garage conversions.
Our Lisburn coverage includes postcode districts BT27 and BT28, and we also work in nearby places such as Belfast, Newtownabbey and Newtownards.
How it works
- 01
Free visit
We look at the property, talk through what you want and measure up. There is no charge and no obligation.
- 02
Design and pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Permissions sorted
Applications, building control and neighbour arrangements, all before the start date.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about side extensions in Lisburn
Do I need planning permission for a side extension in Lisburn?
In Northern Ireland a single-storey side extension can be permitted development if it is no more than 4 metres high, no wider than half the original house and not beside a wall facing a road. Side extensions of more than one storey need planning permission.
Will a two-storey side extension look odd?
Not if it is designed well. Setting it back from the front and keeping the roof lower than the main ridge usually gives a natural look and is what most councils ask for.
Can a side extension go over a drain?
Often yes, with a build-over agreement from the water company or by rerouting the drain. We check this during the survey.
How much does a side extension cost in Lisburn?
In Lisburn, a side extension typically costs £1,450–£2,300 per m² of floor area, including VAT at 20% (standard rate). A typical 28 m² project comes to roughly £40,500–£64,500. Your fixed price depends on the survey and drawings.
How long does it take?
Roughly 10 to 16 weeks on site once approvals are in place, depending on whether it is one or two storeys.
Who approves a side extension in Lisburn?
Planning matters in Lisburn go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.