Mansard conversions for generous space behind a new rear slope.
A mansard changes the rear roof geometry to create a room with far more usable height. It is a bigger architectural move, best handled with careful planning and a clear understanding of the property.
Client photographFull height
Headroom across the main space
Victorian
Well suited to period terraces
Planning
Usually needs formal consent
Bespoke
Designed around the rear elevation
A new rear slope, with much more room behind it
A mansard conversion replaces part of the existing rear roof slope with a steep, near-vertical face, usually set back from the original eaves. The result is a much larger volume of full-height space than a conventional rooflight conversion.
On Victorian terraces and some semis, this can be the only way to create a genuinely comfortable bedroom suite. The trade-off is a more visible external change and a more complex structural and planning process.
- Near-vertical rear face with a shallow upper roof
- Substantial full-height floor area
- Room for bedrooms, bathrooms and storage
- Can create a more architectural rear elevation
A design conversation with the street and the neighbours
Mansard conversions usually require planning permission because they change the roof shape and rear appearance. In conservation areas, the design needs to respond to local character, materials and the way the roof is seen from neighbouring properties.
Party wall matters also need early attention on terraces and semis. We coordinate the drawings, structural information and site arrangements so the approvals process is clear rather than reactive.
Making a larger volume feel calm
The advantage of a mansard is space; the challenge is making it feel considered. Window positions, ceiling heights, the staircase arrival and the bathroom location all need to work together.
We test layouts around real furniture and daily routines before construction. Eaves storage, ensuite drainage and the relationship between the new room and the landing are resolved early, when changes are still inexpensive.
- Layouts tested for beds, wardrobes and desk space
- Bathroom drainage and ventilation considered
- Window and rooflight positions balanced
- External detail coordinated with the existing house
Mansard conversion cost guide
A mansard is a substantial structural change, so the guide range is wider than a standard rear dormer.
| Scope | Typical guide | Typical build time |
|---|---|---|
| Single bedroom mansard | £50,000 – £60,000 | 8–10 weeks |
| Bedroom with ensuite | £60,000 – £75,000 | 10–12 weeks |
| Two-room or premium suite | £70,000 – £90,000+ | 12–14 weeks |
Planning, party wall, structural design and high-specification finishes can all affect the final cost. A survey and written scope are essential.
A clear process. No guesswork.
From the first survey to the final handover, every stage is owned, sequenced and explained.
First conversation
Tell us about the house, the space you need and any constraints you already know about.
Survey & feasibility
We measure the roof, check access and explain which routes are realistic for the property.
Design & quotation
The scope, specification, assumptions, exclusions and payment stages are set out in writing.
Approvals & programme
Planning, structural design, party wall and Building Regulations requirements are coordinated.
Build & handover
The work is sequenced carefully, inspected at the right stages and explained at completion.
Recent work from our own projects.
Every image below is our own work. Any design visualisation is clearly labelled.
Client photographThings worth asking before you begin.
If your question is not here, ask us directly. We would rather explain the position early than have it become a surprise later.
Ask a questionDoes a mansard conversion need planning permission?
Usually, yes. The change to the rear roof shape and appearance normally requires a householder application. Conservation areas and listed buildings bring additional requirements.
Is a mansard suitable for a Victorian terrace?
Victorian terraces are one of the most common candidates, provided the roof structure, party walls, access and planning context allow. The design should respect the terrace rather than compete with it.
How long does a mansard conversion take?
Construction commonly takes eight to twelve weeks, with larger or more detailed projects taking longer. Planning and party wall processes sit before that and can add several months.
Can a mansard include a roof terrace?
Sometimes the upper roof area can be used, but it depends on the design, waterproofing, privacy and planning position. We assess it as part of the proposal rather than assuming it is possible.
Related guidance and services
Let’s talk about the space above your ceiling.
Tell us about your house and what you would like to create. We will explain the realistic options, the approvals likely to be needed and the next practical step.
Oxford & Oxfordshire · Local team