What is a basement conversion?
A basement conversion turns an existing cellar into living space, or excavates a new basement under the house or garden. Waterproofing, structural support and daylight are the main design challenges.
How much does a basement conversion cost in Newtownabbey?
In Newtownabbey, a basement conversion typically costs £1,650–£2,750 per m² for converting an existing cellar, including VAT at 20% (standard rate). For a typical 30 m² project that is roughly £49,500–£82,500. The guide for Newtownabbey 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 (21 m²) | £34,500–£58,000 |
| Typical project (30 m²) | £49,500–£82,500 |
| Larger project (42 m²) | £69,500–£115,500 |
| Rate per m² | £1,650–£2,750 |
The main things that change the cost:
- Waterproofing system
- Lightwells
- Existing cellar or new excavation
- Agreements with neighbours on shared walls
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 basement conversion in Newtownabbey?
Whether you need planning permission depends on your house and its location in Northern Ireland. In Northern Ireland converting an existing cellar usually does not need planning permission; new excavation and external changes may.
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.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
What we take care of:
- Underpinning or new structure where needed
- Lightwells and windows
- Electrics, heating and plastering
- Written agreement with neighbours on shared walls
- Insulation, ventilation and drainage pumps
- Waterproofing design (tanking or cavity drain membrane)
How long does it take?
Build time is typically 8 to 16 weeks for a cellar conversion; longer for new excavation. Allow time beforehand for drawings and approvals, usually 3 to 5 months.
Building in Newtownabbey
Across Northern Ireland, bungalows and chalet bungalows are common, so loft conversions and rear extensions are popular projects.
We work across Newtownabbey and neighbouring areas such as Belfast, Carrickfergus and Bangor. Postcodes we cover in Newtownabbey include BT36 and BT37.
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
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about basement conversions in Newtownabbey
How do you keep a basement dry?
With a waterproofing system designed to BS 8102, typically a cavity drain membrane with a sump pump, or a tanking system.
How much does a basement conversion cost in Newtownabbey?
In Newtownabbey, a basement conversion typically costs £1,650–£2,750 per m² for converting an existing cellar, including VAT at 20% (standard rate). A typical 30 m² project comes to roughly £49,500–£82,500. Your fixed price depends on the survey and drawings.
Can a basement be a bedroom?
Yes, with a suitable escape route such as a lightwell window or protected stair.
Do I need planning permission for a basement conversion in Newtownabbey?
In Northern Ireland converting an existing cellar usually does not need planning permission; new excavation and external changes may.
How long does a basement conversion take in Newtownabbey?
Typically 8 to 16 weeks for a cellar conversion; longer for new excavation. Design and approvals beforehand usually take 3 to 5 months.
Is new excavation worth it?
It can be in high-value areas, but costs are high. We give a feasibility view before design starts.