Mansard Loft Conversions
The most involved conversion, and the one that creates the most usable space
A mansard reconstructs an entire roof slope, usually the rear, as a near-vertical wall set at a steep angle with a flat section at the top, and it's the most substantial type of loft conversion — but also the one that unlocks the most usable floor space and headroom of any option.
Where a dormer extends outward from part of the existing roof, a mansard rebuilds an entire roof slope from close to the ridge down to the wall plate, replacing it with a steeply angled, near-vertical wall and a flat roof section above. The result is close to full-height, full-width usable space across the whole converted area, which is why a mansard is often the choice when the goal is a proper additional storey rather than simply a converted attic. This scale of alteration means it's substantial structural work — most of the existing roof structure on that slope is removed and rebuilt, new walls and roof structure are formed, and because the change to the roof's appearance is significant, mansard conversions generally require planning permission rather than falling under permitted development, particularly on terraced properties or in areas with specific local roofscape considerations. It's a bigger undertaking than a dormer or rooflight conversion in terms of both structural work and time on site, but for properties where the loft genuinely needs to function as a full extra floor — not just a converted room — a mansard delivers space that the other conversion types simply can't match.
When Mansard Loft Conversions Is the Right Choice
- Wanting the loft to function as a genuine extra storey, not just a converted room
- Terraced or period properties where a large-scale rear roof rebuild suits the design
- Projects where maximising headroom and floor area matters more than minimising disruption
- Properties with planning permission already secured or being sought for a roof alteration
- Households prioritising space over the speed or simplicity of a smaller conversion
What's Involved
Design & Planning
We design the new roof form and manage the planning permission process, since mansards typically require full consent.
Roof Reconstruction
The existing roof slope is removed and rebuilt as a near-vertical wall with a flat roof section above.
Structural Work
New walls, structural steelwork and roof structure are formed to carry the substantially altered roof loads.
Fit-Out
The near-full-height new space is insulated, plastered and finished to complete an additional storey of living space.
Local to South Mimms, North London & Hertfordshire
Barnet, the historic market town at the top of Barnet Hill in the London Borough of Barnet, and Hertford, the county town of Hertfordshire, both have terraced and period streets close to their town centres where a mansard's ability to create a genuine extra storey, rather than just a converted attic, makes the most sense of the space available.
Mansard Loft Conversions — FAQ
Q.Why is a mansard more involved than a dormer?
A mansard rebuilds an entire roof slope rather than adding a structure to part of it, so it involves substantially more structural work and, in most cases, formal planning permission rather than permitted development.
Q.Does a mansard conversion always need planning permission?
In most cases yes, since it significantly changes the roof's appearance — we manage this process as part of the project rather than assuming permitted development applies.
Q.Is a mansard worth it compared to a dormer?
It depends on how much space you need — a mansard delivers close to full-height space across the whole converted slope, which suits households wanting a genuine extra floor rather than a single converted room.
Common on These Property Types
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