Mansard loft conversions in Wiltshire

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 Wiltshire?

In Wiltshire, a mansard loft conversion typically costs £66,500–£97,000 for a typical rear mansard, including VAT at 20% (standard rate). Building costs in the South West are close to the UK average, so the figures for Wiltshire are close to our national guide. Design, structural calculations and council fees are extra.

The biggest cost drivers are:

• Roof covering: natural slate costs more
• Number of dormers and lead work
• Bathrooms and finishes
• Scaffolding on busy streets

A guide range is only a starting point: the guide price tool gives an instant figure for your size, and a free survey turns it into a fixed quote.

Do you need planning permission for a mansard loft conversion in Wiltshire?

Here is how the rules work for a mansard loft conversion 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.

At the survey we check your house’s planning history and any restrictions, and tell you which route applies.

What we handle

Handled as part of most mansard loft conversions:

• Dormer windows
• Staircase and fire-safe escape route
• Party wall notices to both neighbours
• Insulation, electrics, plumbing and plastering
• New roof structure, slate or tile covering and lead work
• Structural design and calculations

How long does it take?

Expect 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 Wiltshire

In parts of the South West, protected landscapes and conservation areas shape what can be built, so materials and roof forms are chosen carefully.

Towns we cover in Wiltshire include Swindon, Salisbury, Trowbridge, Chippenham and Melksham.

How it works

1. 01

   Visit and measured survey

   A free visit to understand the project, check access and take measurements.

2. 02

   Design and fixed quote

   Drawings, structural calculations and an itemised, fixed price for the agreed specification.

3. 03

   Approvals

   Planning or permitted development confirmation, building regulations and any party wall matters.

4. 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 Wiltshire