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 Northamptonshire?
In Northamptonshire, a mansard loft conversion typically costs £62,000–£90,000 for a typical rear mansard, including VAT at 20% (standard rate). Building costs in the East Midlands run about 5% below the UK average, and the figures for Northamptonshire are adjusted to reflect that. 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 |
Your quote will depend mainly on:
- Scaffolding on busy streets
- Front, rear or both
- Number of dormers and lead work
- Roof covering: natural slate costs more
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 Northamptonshire?
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.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
Handled as part of most mansard loft conversions:
- Staircase and fire-safe escape route
- Planning drawings and application
- Dormer windows
- Insulation, electrics, plumbing and plastering
- Building control sign-off
- Party wall notices to both neighbours
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 Northamptonshire
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.
Towns we cover in Northamptonshire include Northampton, Corby, Kettering, Wellingborough, Rushden and Daventry.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Design and pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about mansard loft conversions in Northamptonshire
How much does a mansard loft conversion cost in Northamptonshire?
In Northamptonshire, 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.
Can I stay at home?
Usually. The new roof is built under a temporary cover so the house stays dry.
What roof covering is used?
Natural slate is traditional; some councils accept other materials. We follow local guidance.
How long does it take?
Around 9 to 12 weeks on site, plus 2 to 3 months for planning and party wall matters beforehand.
Do you build mansard loft conversions in Northamptonshire?
Yes. We build mansard loft conversions across Northamptonshire, including postcodes CV23, LE15, LE16, MK19 and NN1. Every project starts with a free home visit.