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 County Antrim?
In County Antrim, a mansard loft conversion typically costs £56,000–£81,500 for a typical rear mansard, including VAT at 20% (standard rate). That range is adjusted for Northern Ireland, where domestic building work typically costs around 14% below the national average. 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 |
Your quote will depend mainly on:
- Scaffolding on busy streets
- Number of dormers and lead work
- Agreements with neighbours on shared walls
- Bathrooms and finishes
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 mansard loft conversion in County Antrim?
Here is how the rules work for a mansard loft conversion 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.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
From survey to sign-off, the job normally involves:
- New roof structure, slate or tile covering and lead work
- Planning drawings and application
- Insulation, electrics, plumbing and plastering
- Staircase and fire-safe escape route
- Structural design and calculations
- Written agreement with neighbours on shared walls
How long does it take?
Allow 9 to 12 weeks on site, after planning approval. Before that, surveys, drawings and approvals usually take 3 to 4 months, longer if the council asks for changes.
Building in County Antrim
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 Antrim include Belfast, Lisburn, Newtownabbey, Carrickfergus, Ballymena and Antrim.
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 fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 03
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about mansard loft conversions in County Antrim
Can I stay at home?
Usually. The new roof is built under a temporary cover so the house stays dry.
Who approves a mansard loft conversion in County Antrim?
Planning matters in County Antrim go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
Do I need planning permission for a mansard loft conversion in County Antrim?
In Northern Ireland a mansard needs planning permission from the council.
How much does a mansard loft conversion cost in County Antrim?
In County Antrim, 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.
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.
What roof covering is used?
Natural slate is traditional; some councils accept other materials. We follow local guidance.