What is a mansard loft conversion?
A mansard loft conversion rebuilds the roof with a nearly vertical slope (about 72 degrees) and a flat top, effectively adding a new storey. Small dormer windows sit within the steep slope. Mansards are common on period terraces in towns and cities.
How much does a mansard loft conversion cost in Belfast?
In Belfast, a mansard loft conversion typically costs £56,000–£81,500 for a typical rear mansard, including VAT at 20% (standard rate). Prices across Northern Ireland are typically 14% below the UK average for this kind of work, which is reflected in the range for Belfast. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| A typical rear mansard | £56,000–£81,500 |
| Higher specification | £81,500–£102,000 |
The biggest cost drivers are:
- Front, rear or both
- Number of dormers and lead work
- Agreements with neighbours on shared walls
- Scaffolding on busy streets
A guide range is only a starting point: the guide price tool gives an instant figure for your size, and a free survey turns it into a fixed quote.
Do you need planning permission for a mansard loft conversion in Belfast?
The approval route for Belfast is set by planning law in Northern Ireland. In Northern Ireland a mansard needs planning permission from the council.
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
What we take care of:
- New roof structure, slate or tile covering and lead work
- Insulation, electrics, plumbing and plastering
- Dormer windows
- Planning drawings and application
- Staircase and fire-safe escape route
- Building control sign-off
How long does it take?
Build time is typically 9 to 12 weeks on site, after planning approval. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in Belfast
Across Northern Ireland, bungalows and chalet bungalows are common, so loft conversions and rear extensions are popular projects.
Belfast sits in County Antrim. We cover the whole of Belfast, including postcodes BT1, BT2, BT3 and BT4.
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
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Build and sign-off
We run the build to a written programme and hand over the completion certificate.
Questions about mansard loft conversions in Belfast
Can I stay at home?
Usually. The new roof is built under a temporary cover so the house stays dry.
How much does a mansard loft conversion cost in Belfast?
In Belfast, a mansard loft conversion typically costs £56,000–£81,500 for a typical rear mansard, including VAT at 20% (standard rate). Your fixed price depends on the survey and drawings.
What roof covering is used?
Natural slate is traditional; some councils accept other materials. We follow local guidance.
Do I need planning permission for a mansard loft conversion in Belfast?
In Northern Ireland a mansard needs planning permission from the council.
Do you build mansard loft conversions in Belfast?
Yes. We build mansard loft conversions across Belfast, including postcodes BT1, BT2, BT3 and BT4. Every project starts with a free home visit.
Why choose a mansard over a dormer?
A mansard gives more usable floor space and a neater appearance from the street, but costs more and needs planning permission.