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 Gwynedd?
In Gwynedd, a mansard loft conversion typically costs £60,000–£87,500 for a typical rear mansard, including VAT at 20% (standard rate). That range is adjusted for Wales, where domestic building work typically costs around 8% below the national average. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| A typical rear mansard | £60,000–£87,500 |
| Higher specification | £87,500–£109,500 |
What moves the price most:
- Front, rear or both
- Roof covering: natural slate costs more
- Scaffolding on busy streets
- Bathrooms and finishes
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 Gwynedd?
Whether you need planning permission depends on your house and its location in Wales. In Wales a mansard roof needs planning permission and is judged against local design guidance.
The Party Wall etc. Act 1996 applies in Wales, so notices must be served before work on a shared wall, on the boundary, or excavation close to a neighbour’s foundations.
At the survey we check your house’s planning history and any restrictions, and tell you which route applies.
What we handle
On a typical mansard loft conversion we handle:
- Planning drawings and application
- Party wall notices to both neighbours
- Dormer windows
- Structural design and calculations
- New roof structure, slate or tile covering and lead work
- Insulation, electrics, plumbing and plastering
How long does it take?
Expect 9 to 12 weeks on site, after planning approval. Allow time beforehand for drawings and approvals, usually 3 to 4 months.
Building in Gwynedd
Terraced houses in Welsh towns often have narrow plots, which suits rear and side return extensions and rear dormers.
Towns we cover in Gwynedd include Bangor, Llandudno, Holyhead and Caernarfon.
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 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 Gwynedd
Why choose a mansard over a dormer?
A mansard gives more usable floor space and a neater appearance from the street, but costs more and needs planning permission.
How long does a mansard loft conversion take in Gwynedd?
Typically 9 to 12 weeks on site, after planning approval. Design and approvals beforehand usually take 3 to 4 months.
Can I stay at home?
Usually. The new roof is built under a temporary cover so the house stays dry.
Do I need planning permission for a mansard loft conversion in Gwynedd?
In Wales a mansard roof needs planning permission and is judged against local design guidance.
How much does a mansard loft conversion cost in Gwynedd?
In Gwynedd, a mansard loft conversion typically costs £60,000–£87,500 for a typical rear mansard, including VAT at 20% (standard rate). Your fixed price depends on the survey and drawings.
Do I need party wall agreements?
Yes, mansards on terraced houses almost always involve both party walls.