Mansard
Mansard Loft Conversions in Bromley
The largest loft conversion there is. Rebuilding the roof to near-vertical to create a full storey rather than a room in the roof.
A Floor, Not a Loft
A mansard rebuilds the roof structure so the rear wall rises at around 72 degrees, almost vertical, with a shallow, nearly flat roof on top. The result does not feel like a loft conversion at all. It feels like a floor of the house, because that is effectively what it is.
That makes it the most expensive option on this site and the most disruptive, and it is why mansards cluster where the houses are larger and the ceilings are higher to start with. The period stock around Chislehurst, Bickley and Dulwich rather than the interwar semis.
When a Mansard is Worth It
- You want two rooms or a bedroom-and-bathroom suite rather than one room.
- The existing roof is too shallow for a dormer to rescue.
- The house is a larger period property where the proportions can carry it.
- You are staying put long enough for the spend to make sense.
Be aware of the trade: a mansard almost always needs planning permission. It changes the roof profile substantially, and it is very difficult to keep inside the permitted development conditions, particularly the rule that no part may exceed the height of the highest part of the existing roof, and the requirement that materials match.
What the Work Involves
Full Structural Design
A mansard alters the roof more than any other conversion, so the calculations cover the whole roof, not one slope.
Stripping the Roof
Most of the existing roof comes off. This is the most exposed and most weather-dependent stage of any conversion.
Rebuilding to Near-Vertical
New rear wall at around 72 degrees, with a shallow roof above it.
Party Wall Upstands
On a terrace or semi, the shared walls usually need building up to the new roof line.
Floor and Stairs
New floor on steels, and a staircase to what is effectively a new storey.
Fit-Out and Sign-Off
Full internal finish plus building control approval at each stage.
Mansard Costs in Bromley
| Conversion type | Estimated cost in Bromley |
|---|---|
| Mansard | £65,000 – £120,000 |
Figures are estimates for guidance only, based on published 2026 ranges and prices advertised locally. Every loft is different. The only accurate number is a quote from a surveyor who has been up in yours.
Planning Permission for a Mansard
Assume you need it. A mansard is the type least likely to fit inside Class B, and the houses that suit a mansard are disproportionately the ones in Bromley's 47 conservation areas, where Class B does not apply at all and a full application is required regardless.
That is not a reason not to build one. It is a reason to get the planning position established before you spend money on detailed design. The planning guide covers what that process looks like.
This is general information, not planning advice. Permitted development rights depend on your specific property, what has already been built, and whether the address falls in a conservation area or under an Article 4 direction. Check your address on Bromley Council's own map, and take professional advice before committing to anything.
Why Start Here
We are Not Quoting You
We do not carry out the work, so we gain nothing from talking you into a bigger conversion than your roof needs. A building company quoting you is in a different position.
Specialists Who Cover Your Postcode
Your enquiry goes to loft conversion companies actually working in your part of the borough and currently taking work, not a national list.
Bromley Rules, Not National Boilerplate
Forty-seven conservation areas and an Article 4 direction that removes rights most guides assume you have. We cover what applies here.
Nothing Owed, Nothing Booked
Quotes are free and there is no obligation at any point. On a job this size, take two or three of them.
Find Out What Your Loft Conversion Would Cost
Tell us about your house and what you want the loft for. We will pass it to loft specialists covering your area, and they will come back to you with a quote. No obligation, no pressure.
Areas We Cover for Mansard Conversions
Mansards suit larger period houses where the proportions carry the change, and where the planning position needs checking first.
Other Conversion Types
Not sure this is the right conversion for your house? The other types are below, and the types of loft conversion guide compares them properly, including the lofts that cannot be converted at all.