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Every type of London loft conversion, explained

What each conversion involves, which houses it suits and where planning usually lands. Not sure which fits your roof? That’s what the survey is for.

Mansard loft conversions

A mansard rebuilds the rear roof slope at roughly 70 degrees with a flat roof on top, so the new floor has full-height walls almost all the way across. Inside it feels like a proper extra storey rather than a room in the roof.

It’s the London classic, particularly on terraces where neighbouring roofs have already been mansarded. Because it changes the roof shape so visibly, it almost always needs planning permission, and many boroughs publish design guidance covering the pitch, the materials and the window style. We work to that guidance from the first drawing.

Good fit for

  • Terraces where every square metre counts
  • Two rooms, or a bedroom suite with bathroom
  • Streets where neighbours already have mansards
  • Homeowners happy to go through planning

What’s involved

  • Planning route agreed and submitted before work starts
  • Party wall notices served on both neighbours
  • Rear slope rebuilt steeply, flat roof formed and waterproofed
  • Windows and any Juliet balcony set into the new face
  • Structure, insulation, electrics, plastering and finishing
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L-shaped dormer conversions

Most Victorian and Edwardian terraces have a rear outrigger, the narrow back addition over the kitchen or bathroom. An L-shaped dormer runs a rear dormer along the main roof and wraps it around into the outrigger, forming an L.

It’s the biggest space gain available on a terrace short of a mansard, and it usually lands a double bedroom, a bathroom and a landing on one floor. Where permitted development still applies, an L-shape can often be built under it, subject to the volume allowance.

Good fit for

  • Victorian and Edwardian terraces with a back addition
  • Bedroom plus bathroom in one conversion
  • Keeping the front of the house unchanged
  • Houses where a mansard would be refused

What’s involved

  • Volume checked against the permitted development allowance
  • Main roof dormer and outrigger dormer framed together
  • Roofs tied in and made watertight
  • Windows, rooflights and Juliet balcony fitted
  • Internal layout, bathroom, plastering and finishing
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Rear dormer conversions

A rear dormer is a box built out from the back roof slope. It replaces sloping ceiling with vertical wall, so you get standing height and usable floor right to the back of the house.

It’s the workhorse conversion on London semis and 1930s houses: good space, a straightforward build and often no planning application needed. Pair it with French doors and a Juliet balcony and the room opens onto the garden.

Good fit for

  • Semis and 1930s houses
  • A double bedroom with a shower room
  • Lofts that lack head height under a pitched roof
  • Garden views through French doors

What’s involved

  • Floor strengthened and the rear slope opened up
  • Dormer framed, roofed and made watertight
  • Cheeks tile-hung, slated or clad to match the street
  • Windows, rooflights and Juliet balcony fitted
  • Insulation, electrics, plastering and finishing
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Hip-to-gable conversions

Plenty of London semis and detached houses, especially interwar ones in the outer boroughs, have a hipped roof where the side slopes inwards. That slope eats the loft and often leaves nowhere for a staircase to land.

Building the hip up into a vertical gable wall extends the ridge to the end of the house and opens the whole roof. It’s usually combined with a rear dormer, which together give the largest room a semi can offer.

Good fit for

  • Semis and detached houses with a hipped roof
  • Lofts where a staircase won’t currently fit
  • The largest possible room on a semi
  • Pairing with a rear dormer

What’s involved

  • Hipped end removed and gable wall built up
  • Ridge extended and roof re-covered to match
  • Rear dormer added where required
  • Staircase run up in line with the existing stairs
  • Insulation, electrics, plastering and finishing
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Rooflight (Velux) loft conversions

A rooflight conversion leaves the roof shape untouched. The floor is strengthened, the roof insulated, and rooflights are set into the existing slope to bring in daylight.

It’s the quickest and least disruptive option, and the one most likely to be allowed where the roof faces the street or sits in a conservation area. It needs a loft that already has the height.

Good fit for

  • Lofts with good existing head height
  • Home offices, studies and guest rooms
  • Front roof slopes and sensitive streets
  • Keeping the outside of the house unchanged

What’s involved

  • Joists strengthened to take a habitable room
  • Rooflights fitted into the existing slope
  • Roof insulated between and under the rafters
  • Eaves storage built into the low sides
  • Staircase, electrics, plastering and finishing
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New loft staircase with white spindles, oak handrail and newel caps leading up from the first floor landing

Loft staircases

The staircase is what turns a loft into part of the house. On a London terrace it usually has to rise over the existing flight without stealing a bedroom, which takes careful setting out and a check on headroom against Building Regulations.

We design the stairs around your landing and fit them complete with spindles, handrail and balustrade, moving electrics and making good the plastering around them. If you’ve inherited a steep or unsafe loft stair, replacing it changes how the room gets used.

Good fit for

  • Terraces with tight landings
  • Replacing a loft ladder with permanent stairs
  • Steep or unsafe stairs in an existing loft
  • Matching the style of your main staircase

What’s involved

  • Set out over the existing flight wherever possible
  • Headroom checked against Building Regulations
  • Stairs, spindles, handrail and balustrade fitted
  • Electrics moved where needed
  • Plastering and making good around the new stairs
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Loft bathroom under the eaves with wall-hung WC, basin and freestanding bath beside the new staircase

Loft bathrooms and ensuites

A loft bathroom has to work around two things: where you can stand up, and where the waste can run. We plan both at survey stage, usually stacking the new bathroom above the existing one to keep the pipework short.

Dormers and mansards give the head height a shower needs; under a rooflight conversion a bath under the slope often works better. We tile, fit and finish it as part of the conversion.

Good fit for

  • Turning the loft into a main bedroom suite
  • Taking pressure off one family bathroom
  • Dormer and mansard conversions
  • Guest and teenage bedrooms

What’s involved

  • Layout planned around head height and drainage
  • Waste run tied into the existing stack
  • Extraction, lighting and underfloor heating wired in
  • Tanking, tiling, shower or bath fitted
  • Sealed and finished ready to use
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Loft bedroom with sage green walls, black French doors onto a Juliet balcony and wall-mounted air conditioning

Juliet balconies and French doors

French doors with a Juliet balcony give a rear dormer or mansard proper daylight and a view over the gardens, without needing a platform to stand on.

Because there’s nothing to stand on, a Juliet balcony is generally acceptable under permitted development where a raised terrace would not be. Glass or black metal, both work on a London rear elevation.

Good fit for

  • Rear dormers and mansards
  • Loft bedrooms that need light and air
  • Frameless glass for a modern finish
  • Black metal rails on period houses

What’s involved

  • Opening framed into the dormer or mansard face
  • French doors fitted and sealed
  • Glass or metal balustrade fixed across the opening
  • Finished internally with the rest of the room
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Painted loft stairs with a herringbone runner leading up to a bright loft room with rooflight and built-in drawers

Existing loft conversions, put right

A lot of London houses come with a loft room that was converted years ago, cheaply, or without Building Control sign-off. It might have a ladder instead of stairs, thin insulation, an unsafe escape route, or no paperwork for your buyer’s solicitor.

We can strip it back and rebuild it properly, or fix only the parts letting it down: the staircase, insulation, rooflights, fire safety, electrics or plastering.

Good fit for

  • Houses bought with a dated or unapproved loft
  • Rooms that are freezing in winter and baking in summer
  • Replacing a ladder with a staircase
  • Adding a bathroom to an existing loft

What’s involved

  • Survey of what’s there and what’s missing
  • Strip-out where the structure isn’t up to it
  • Structure, insulation and fire safety brought up to standard
  • New staircase, rooflights, electrics and plastering
  • Finished so it reads as part of the house
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The five conversion types side by side

Planning depends on your address, your borough and the size of the conversion. This is the general picture, not a promise for your street.

TypeRoof shapeSpace gainedPlanning permission needed?Typically suits
MansardRear slope rebuilt near-vertical with flat topLargest gain, close to a full storeyUsually yesTerraces, especially inner London
L-shaped dormerDormer wrapped into the rear outriggerVery large, often two roomsOften not, if within the volume allowanceVictorian and Edwardian terraces
Rear dormerBox built out from the back slopeLarge gain across the backOften not, if within the volume allowanceSemis and 1930s houses
Hip-to-gableHipped side built up into a gableLarge, plus room for the stairsOften not, if within the volume allowanceSemis and detached with hipped roofs
Rooflight (Velux)UnchangedUses the height already thereRarelyLofts with good existing head height

Questions about conversion types

More answers on the home page, or call 020 3769 7040.

Mansard or L-shaped dormer, which gives more space?

A mansard, usually. It rebuilds the whole rear slope so you get full height across the floor. An L-shaped dormer gains less, but it often stays within permitted development and avoids a planning application, which can make it faster and more certain.

Do rooflight conversions need planning permission?

Normally not. Rooflights usually count as permitted development as long as they project no more than 150mm from the slope and the house isn’t a flat or covered by an Article 4 direction. Building Control approval is still needed for the conversion itself.

Where will the new staircase go?

Ideally straight up over the existing flight, so nothing is lost from the floor below. On narrow terraces we sometimes turn the flight or borrow a little from the landing. It is one of the first things we set out at survey.

Can you build a mansard in a conservation area?

Often yes, but it goes through planning and has to follow the borough’s design guidance on pitch, materials and windows. Where neighbouring properties already have mansards, the case is usually stronger. We check the local policy before you commit to anything.

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