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 Lisburn?
In Lisburn, 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 |
The main things that change the cost:
- Roof covering: natural slate costs more
- Number of dormers and lead work
- Front, rear or both
- Scaffolding on busy streets
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 Lisburn?
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.
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 mansard loft conversion we handle:
- New roof structure, slate or tile covering and lead work
- Dormer windows
- Staircase and fire-safe escape route
- Planning drawings and application
- Written agreement with neighbours on shared walls
- Structural design and calculations
How long does it take?
Expect 9 to 12 weeks on site, after planning approval. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in Lisburn
Across Northern Ireland, bungalows and chalet bungalows are common, so loft conversions and rear extensions are popular projects.
Projects in Lisburn (BT27 and BT28) are surveyed in person before we quote, so the price reflects your actual property.
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 mansard loft conversions in Lisburn
What roof covering is used?
Natural slate is traditional; some councils accept other materials. We follow local guidance.
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.
Do I need planning permission for a mansard loft conversion in Lisburn?
In Northern Ireland a mansard needs planning permission from the council.
How much does a mansard loft conversion cost in Lisburn?
In Lisburn, 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.
How long does a mansard loft conversion take in Lisburn?
Typically 9 to 12 weeks on site, after planning approval. Design and approvals beforehand usually take 3 to 4 months.
Can I stay at home?
Usually. The new roof is built under a temporary cover so the house stays dry.