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 Derby?
In Derby, a mansard loft conversion typically costs £62,000–£90,000 for a typical rear mansard, including VAT at 20% (standard rate). Prices across the East Midlands are typically 5% below the UK average for this kind of work, which is reflected in the range for Derby. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| A typical rear mansard | £62,000–£90,000 |
| Higher specification | £90,000–£112,500 |
The main things that change the cost:
- Scaffolding on busy streets
- Party wall surveyor fees
- Number of dormers and lead work
- Front, rear or both
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 Derby?
Whether you need planning permission depends on your house and its location in England. In England a mansard almost always needs planning permission because it changes the roof shape. Many councils publish design guidance for mansards on terraced streets, and some streets are more likely to be approved where neighbours already have one.
Building regulations approval comes from the council’s building control service or a registered building control approver. The work is inspected at key stages, such as foundations, drainage and insulation, and a completion certificate is issued 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
Handled as part of most mansard loft conversions:
- Planning drawings and application
- Building control sign-off
- Dormer windows
- Insulation, electrics, plumbing and plastering
- Staircase and fire-safe escape route
- New roof structure, slate or tile covering and lead work
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 Derby
In the East Midlands, many estates built since the 1960s have integral garages that convert well into a study or bedroom.
Our Derby coverage includes postcode districts DE1, and we also work in nearby places such as Belper, Ilkeston and Heanor.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Permissions sorted
Applications, building control and neighbour arrangements, all before the start date.
- 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 Derby
How much does a mansard loft conversion cost in Derby?
In Derby, a mansard loft conversion typically costs £62,000–£90,000 for a typical rear mansard, including VAT at 20% (standard rate). Your fixed price depends on the survey and drawings.
Do I need party wall agreements?
Yes, mansards on terraced houses almost always involve both party walls.
Does a mansard need planning permission?
Almost always, because it changes the roof shape. Councils assess it against local design 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.
How long does a mansard loft conversion take in Derby?
Typically 9 to 12 weeks on site, after planning approval. Design and approvals beforehand usually take 3 to 4 months.