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 March?
In March, a mansard loft conversion typically costs £69,000–£100,500 for a typical rear mansard, including VAT at 20% (standard rate). Building costs in the East of England run about 6% above the UK average, and the figures for March are adjusted to reflect that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| A typical rear mansard | £69,000–£100,500 |
| Higher specification | £100,500–£125,500 |
What moves the price most:
- Scaffolding on busy streets
- Number of dormers and lead work
- Roof covering: natural slate costs more
- Party wall surveyor fees
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 March?
The approval route for March is set by planning law 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.
At the survey we check your house’s planning history and any restrictions, and tell you which route applies.
What we handle
What we take care of:
- Building control sign-off
- Party wall notices to both neighbours
- Planning drawings and application
- Structural design and calculations
- Insulation, electrics, plumbing and plastering
- Staircase and fire-safe escape route
How long does it take?
Allow 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 March
Many towns in the East of England have estates built since the 1970s, where garage conversions and rear extensions are popular.
Projects in March (PE15) are surveyed in person before we quote, so the price reflects your actual property.
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
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 March
Can I stay at home?
Usually. The new roof is built under a temporary cover so the house stays dry.
How long does a mansard loft conversion take in March?
Typically 9 to 12 weeks on site, after planning approval. Design and approvals beforehand usually take 3 to 4 months.
Does a mansard need planning permission?
Almost always, because it changes the roof shape. Councils assess it against local design guidance.
Do I need party wall agreements?
Yes, mansards on terraced houses almost always involve both party walls.
How much does a mansard loft conversion cost in March?
In March, a mansard loft conversion typically costs £69,000–£100,500 for a typical rear mansard, including VAT at 20% (standard rate). Your fixed price depends on the survey and drawings.