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 Downpatrick?
In Downpatrick, 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. Building costs in Northern Ireland run about 14% below the UK average, and the figures for Downpatrick are adjusted to reflect that. 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:
- Floor lowering and underpinning
- Lightwells
- Ground water and access
- Agreements with neighbours on shared walls
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 basement conversion in Downpatrick?
The approval route for Downpatrick is set by planning law in Northern Ireland. In Northern Ireland converting an existing cellar usually does not need planning permission; new excavation and external changes may.
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.
At the survey we check your house’s planning history and any restrictions, and tell you which route applies.
What we handle
On a typical basement conversion we handle:
- Structural and ground survey
- Written agreement with neighbours on shared walls
- Electrics, heating and plastering
- Lightwells and windows
- Waterproofing design (tanking or cavity drain membrane)
- Insulation, ventilation and drainage pumps
How long does it take?
Allow 8 to 16 weeks for a cellar conversion; longer for new excavation. Design and approvals come first and typically take 3 to 5 months, depending on the approval route.
Building in Downpatrick
Northern Ireland has many detached and semi-detached homes on generous plots, which suits single-storey rear extensions and garage conversions.
Our Downpatrick coverage includes postcode districts BT30, and we also work in nearby places such as Newtownards, Lisburn and Belfast.
How it works
- 01
Survey and brief
We visit, discuss your ideas and budget, and survey the property or site at no cost.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about basement conversions in Downpatrick
How much does a basement conversion cost in Downpatrick?
In Downpatrick, 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.
Do I need planning permission for a basement conversion in Downpatrick?
In Northern Ireland converting an existing cellar usually does not need planning permission; new excavation and external changes may.
Is new excavation worth it?
It can be in high-value areas, but costs are high. We give a feasibility view before design starts.
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 long does a basement conversion take in Downpatrick?
Typically 8 to 16 weeks for a cellar conversion; longer for new excavation. Design and approvals beforehand usually take 3 to 5 months.
Can a basement be a bedroom?
Yes, with a suitable escape route such as a lightwell window or protected stair.