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 Worthing?
In Worthing, a mansard loft conversion typically costs £73,000–£106,500 for a typical rear mansard, including VAT at 20% (standard rate). That range is adjusted for the South East, where domestic building work typically costs around 12% above the national average. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| A typical rear mansard | £73,000–£106,500 |
| Higher specification | £106,500–£133,000 |
What moves the price most:
- Party wall surveyor fees
- Scaffolding on busy streets
- Front, rear or both
- Number of dormers and lead work
Use the guide price tool to see how size and specification change the figure, then ask for a written, itemised quote.
Do you need planning permission for a mansard loft conversion in Worthing?
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.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
What we take care of:
- Structural design and calculations
- Building control sign-off
- Planning drawings and application
- New roof structure, slate or tile covering and lead work
- Party wall notices to both neighbours
- Insulation, electrics, plumbing and plastering
How long does it take?
The build itself usually takes 9 to 12 weeks on site, after planning approval. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in Worthing
The South East has a broad mix of housing, from Victorian terraces in the towns to post-war semis and newer estates, so extension types vary street by street.
We work across Worthing and neighbouring areas such as Lancing, Shoreham-by-Sea and Portslade. Postcodes we cover in Worthing include BN11, BN91 and BN99.
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
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 Worthing
Can I stay at home?
Usually. The new roof is built under a temporary cover so the house stays dry.
Do you build mansard loft conversions in Worthing?
Yes. We build mansard loft conversions across Worthing, including postcodes BN11, BN91 and BN99. Every project starts with a free home visit.
How much does a mansard loft conversion cost in Worthing?
In Worthing, a mansard loft conversion typically costs £73,000–£106,500 for a typical rear mansard, including VAT at 20% (standard rate). Your fixed price depends on the survey and drawings.
What roof covering is used?
Natural slate is traditional; some councils accept other materials. We follow local guidance.
Do I need party wall agreements?
Yes, mansards on terraced houses almost always involve both party walls.