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 County Londonderry?
In County Londonderry, 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 County Londonderry 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 |
Your quote will depend mainly on:
- Steel work where the side wall is opened
- Drains, gas meters or soil pipes that need moving
- Roof design and tile matching
- Internal fit-out of the new rooms
For a figure based on your own measurements, try the guide price tool, then book a free home visit for a fixed quote.
Do you need planning permission for a side extension in County Londonderry?
Here is how the rules work for a side extension 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.
In Northern Ireland building control approval comes from the council, usually through a full plans application or a building notice, with inspections during the work and a completion certificate at the end.
We check this for your address before design work starts, so there are no surprises later.
What we handle
From survey to sign-off, the job normally involves:
- Opening into the existing house
- Survey of the boundary, drains and access
- Planning drawings and application
- Building control completion
- Walls, roof and windows to match the house
- Foundations and drainage alterations
How long does it take?
Build time is typically 10 to 16 weeks on site depending on size and storeys. Before that, surveys, drawings and approvals usually take 3 to 4 months, longer if the council asks for changes.
Building in County Londonderry
Northern Ireland has many detached and semi-detached homes on generous plots, which suits single-storey rear extensions and garage conversions.
Towns we cover in County Londonderry include Derry, Coleraine, Limavady and Magherafelt.
How it works
- 01
Survey and brief
We visit, discuss your ideas and budget, and survey the property or site at no cost.
- 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 County Londonderry
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.
Do I need planning permission for a side extension in County Londonderry?
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.
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.
Do you build side extensions in County Londonderry?
Yes. We build side extensions across County Londonderry, including postcodes BT28, BT45, BT46, BT47 and BT48. Every project starts with a free home visit.
How much does a side extension cost in County Londonderry?
In County Londonderry, 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.