Ideas Library · Roof Design
Mansard Roof: Gaining a Storey Inside the Silhouette
Change the roof geometry itself rather than cutting into a given roof: a steep lower plane gives near-vertical walls to the top floor while a shallow upper plane keeps the ridge and the apparent height where they were.
Spaces:Whole roofTop floor within the roofStreet elevationDormer face
Style:Period-inspiredUrbanTraditionalContemporary
Where this idea works
Where this idea works
Contexts this direction tends to suit — and, honestly, where it may not.
- Buildings where extra floor area is wanted but height is constrained
- Streets where roofs of this profile already sit comfortably
- Owners who want the added storey to read as roof rather than as an extra floor
- Plans where near-vertical walls at the top floor make the space genuinely usable
Where it may not fit
Where it may not fit
- Roofs whose structure cannot carry a changed geometry without a qualified professional's assessment
- Settings where the roof profile is controlled — confirm with the relevant authority
- Situations where escape, access or floor-level requirements are unresolved — a question for a qualified professional
Planning
Planning considerations
- Two planes means two conditions: the steep face behaves almost like a wall, the shallow one almost like a flat roof
- The change of angle is a visible line all the way round, so decide where it sits in relation to the floor inside
- Windows on the steep face usually arrive as dormers, so their rhythm is decided with the form, not after it
- Adding habitable space inside a roof brings requirements to confirm with a qualified professional and the relevant authority
Layout
Layout considerations
- The steep plane returns useful wall height at the room's edge, which is what the form buys
- The shallow upper plane makes the ceiling flat across the middle of the room
- Corner conditions on the steep plane are awkward, so keep fitted joinery away from them
- Stair arrival needs headroom under the shallow plane rather than under the steep one
Materials & finishes
Materials and finishes to discuss
Named generically as starting points to discuss with professionals — not specifications, and not priced.
Consider:Slate or tile on the steep planeMembrane or metal on the shallow planeDormer cheeks and flashingsLeadwork or metal detailingEaves and cornice trim
- Ask how the junction between the two planes is weathered, since water passes from a shallow fall to a steep one there
- Discuss how the near-vertical covering is fixed and how it sheds at its base
- Confirm how dormer cheeks and their flashings are detailed on an exposed elevation
Maintenance & durability
Maintenance and durability questions
- The shallow upper plane is out of sight from the ground, so ask how its condition is checked
- Discuss how the steep face and its dormers are reached for repair given their height
Professional review
What to ask a qualified professional
Bring these questions to a designer, contractor or the relevant qualified professional or authority.
- Would this geometry change the structure and the load path in ways you would need to assess?
- How would you weather the junction where the steep plane meets the shallow one?
- What would I need to confirm with the relevant authority about a habitable floor inside the roof?
- Which coverings would you suggest discussing for a near-vertical roof plane?
- How would the upper plane be inspected and maintained once it is out of sight?
More ideas
Related ideas
Level-Change Floor Transition →Handling flooring where floor levels differ — step-downs, sunken zones and edges that read clearly and safely, framed as owner-side planning inspiration.Geometric Patterned Tile Floor →Arranging tiles into a repeating geometric pattern turns the floor into a centrepiece, a direction where setting-out and cut placement carry the whole look.Open-Plan Zoning →An educational look at defining cooking, dining and living zones in one open room using rugs, lighting, level and ceiling cues rather than partitions.Roofline & Eaves Detailing →Explore how fascia, soffit and eaves detailing shape the crown of an elevation, plus the questions to confirm before refining these edges.Acoustic Underlay Floors →An acoustic underlay beneath the finish floor aims to soften impact and airborne sound between levels, a direction worth exploring in multi-storey homes.Border & Inlay Floors →Framing a floor with a contrasting border or feature inlay to define edges and entries, focusing on setting-out, framed as owner-side inspiration.Broken-Plan Floor Zoning →Defining zones in a large open-plan space by switching floor material, using the seam as a boundary between functions, framed as owner-side inspiration.Asymmetric Pitch →Explore shifting the ridge off the centreline so one slope runs long and shallow and the other short and steep above the rooms.
Related guides
Related Build Design Hub guides
Roof Design Ideas
Educational roof design inspiration — roof form, edge condition, the plane seen from above and the shape read from inside, framed as directions to explore before speaking with professionals.
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