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Lofts and upward extensions

Mansard loft conversions

Steep-sided roof extensions that add a whole new storey. Designed, approved and built by SK Residential, with a fixed price in writing for the agreed specification.

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What is a mansard loft conversion?

A mansard loft conversion replaces one or both slopes of a roof with a near-vertical wall, typically at 70 degrees, with small dormer windows set into it. It creates almost a full extra storey and is common on terraced houses in towns and cities, particularly in London.

London Victorian terrace with a slate mansard roof and lead-clad dormer windows

Mansards are a bigger structural job than other conversions because the roof is largely rebuilt. They normally need planning permission, and many councils have design guides setting the angle, materials and window style. We prepare the design to those guides and build in slate, lead and timber or approved alternatives.

Typical time on site
10 to 14 weeks
Guide price
£65,000 to £110,000
Building regulations
Required

What is included?

  • Planning application to local design guidance
  • Structural design and party wall process
  • Roof removal and new mansard frame
  • Slate cladding and lead-clad dormers
  • Staircase, insulation and fit-out
  • En-suite, electrics and fire safety

How much does a mansard loft conversion cost?

A rear mansard on a Victorian terrace typically costs around £65,000 to £85,000 including VAT, more in central London.

Mansard loft conversionsGuide price incl. VAT
Rear mansard£65,000 to £85,000
Front and rear (double) mansard£80,000 to £110,000

Unit: per conversion. Guide ranges only; your price is fixed in writing after the survey.

Use the guide price tool for a figure based on your size and specification, or see all guide prices.

Does a mansard loft conversion need planning permission?

England

Mansard conversions change the shape of the roof significantly, so they usually need planning permission in England. Many councils publish guidance on mansard design. Where several houses on a terrace already have mansards, approval is often easier.

Wales

This needs full planning permission from your council in Wales. We prepare and submit the application and deal with the planning officer on your behalf.

Scotland

This needs planning permission and a building warrant from your council in Scotland before work starts. We prepare both applications.

Northern Ireland

This needs full planning permission from the council in Northern Ireland, plus building control approval.

What about building regulations?

Full building regulations approval, including a new roof structure, fire separation from neighbours and a protected escape route.

What should I think about before starting?

  • A mansard nearly always involves party walls on both sides of a terrace.
  • The roof is open for longer than with a dormer, so weather protection matters.
  • Council design guides often require natural slate and lead.
  • Scaffolding and a temporary roof are usually needed.

How does the project run?

  1. Tell us about the project. Call, use the guide price tool or send the form with a few photos and a postcode.
  2. Free site visit. We measure up, look at access, drains and the structure, and talk through options and budget.
  3. Design and fixed price. You get drawings and a written price for the agreed specification before anything is ordered.
  4. Build and hand over. Our teams build to the programme, building control inspects, and you get the completion paperwork at the end.

Questions about mansard loft conversions

How much does a mansard loft conversion cost?

Typically £65,000 to £110,000 including VAT, depending on whether one or both roof slopes are rebuilt.

Does a mansard need planning permission?

Almost always, because it changes the roof profile.

How long does a mansard take?

Around 10 to 14 weeks on site after planning approval.

Why choose a mansard over a dormer?

A mansard gives more usable space and often fits a street better where neighbours already have one.

Will I need party wall agreements?

Very likely, as the work affects the walls shared with both neighbours on a terrace.

Related projects

Guides

Where do we build mansard loft conversions?

We take on mansard loft conversions across England, Wales, mainland Scotland and Northern Ireland. Choose your area:

Planning an extension, loft or new home?

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