Mansard loft conversion plans in Kensington and Chelsea

Always. A mansard rebuilds the roof into a steep rear slope with a flat top, and that wholesale change of roof shape is well outside permitted development — so it needs a full householder application to the Royal Borough of Kensington and Chelsea on every street, designated or not. On a terrace in a conservation area such as Chelsea and Kensington the roofline is protected, so the design is scrutinised more closely still.

It is a rebuilt roof with a steep, near-vertical rear slope and a small flat top, which creates almost a full extra storey inside — far more than a dormer returns. Kensington and Chelsea's period terraces are the classic mansard candidates, and where a row already carries mansards a new one that matches the line is the most likely of all lofts to be approved despite being the largest. the Royal Borough of Kensington and Chelsea is the decision-maker.

Because it reshapes the whole roof rather than adding a box to it. The steep slope pushes the walls out almost to vertical and the flat top lifts the ceiling, so the usable floor runs nearly the full footprint of the house at head height — close to a complete storey. That is why, in Kensington and Chelsea, a mansard is chosen when a dormer or hip-to-gable will not give enough room. the Royal Borough of Kensington and Chelsea is the decision-maker.

It can, but the case is harder. Where a terrace already has a consistent mansard line, matching it is straightforward; on an unbroken row, the Royal Borough of Kensington and Chelsea weighs whether your mansard would break the skyline or could set an acceptable pattern for the street. We draw the design to sit within the terrace and make that argument on the elevations rather than leave it to chance.

Almost certainly, on both sides. A mansard rebuilds the roof up to and across the party walls with the neighbours either side, so the Party Wall etc. Act applies to each and notice must be served before work starts — separately from the Royal Borough of Kensington and Chelsea's planning decision. We detail both party walls on the drawings and flag the notices early so surveyors can be appointed without holding up the build.

We price each Kensington and Chelsea mansard individually, because the terrace, the roofline match and the party-wall detailing vary street to street, and send a fixed, no-obligation quote within one working day. It covers the full drawing pack with free revisions until the Royal Borough of Kensington and Chelsea approves, and we confirm the roofline case at the outset. Call 020 7864 7245 to start.