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 Daventry?
In Daventry, a mansard loft conversion typically costs £62,000–£90,000 for a typical rear mansard, including VAT at 20% (standard rate). That range is adjusted for the East Midlands, where domestic building work typically costs around 5% below the national average. 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:
- Party wall surveyor fees
- Front, rear or both
- Scaffolding on busy streets
- Bathrooms and finishes
For a figure based on your own measurements, try the guide price tool, then book a free home visit for a fixed quote.
Do you need planning permission for a mansard loft conversion in Daventry?
Before anything is built in Daventry, we confirm which approvals apply 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.
Where work involves a shared wall, building on the boundary, or digging foundations within 3 metres of a neighbour’s building and deeper than its foundations (or within 6 metres for deeper work), the Party Wall etc. Act 1996 applies and notices must be served before work starts.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
On a typical mansard loft conversion we handle:
- Party wall notices to both neighbours
- Structural design and calculations
- Insulation, electrics, plumbing and plastering
- Staircase and fire-safe escape route
- New roof structure, slate or tile covering and lead work
- Dormer windows
How long does it take?
Build time is typically 9 to 12 weeks on site, after planning approval. Design and approvals come first and typically take 3 to 4 months, depending on the approval route.
Building in Daventry
The East Midlands has a mix of red-brick terraces, inter-war semis and newer estates, so rear extensions and garage conversions are common projects.
From NN11 outwards, we take on projects throughout Daventry and the surrounding parts of Northamptonshire.
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
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 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 Daventry
How much does a mansard loft conversion cost in Daventry?
In Daventry, 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.
Does a mansard need planning permission?
Almost always, because it changes the roof shape. Councils assess it against local design guidance.
How long does a mansard loft conversion take in Daventry?
Typically 9 to 12 weeks on site, after planning approval. Design and approvals beforehand usually take 3 to 4 months.
Do I need party wall agreements?
Yes, mansards on terraced houses almost always involve both party walls.
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.