Guide · Updated 2026
How much does a loft conversion cost in London?
Short answer: most London loft conversions land somewhere between £45,000 and £95,000. That is a wide range because the number depends far more on your roof than on your taste. Here is what actually moves it.
Typical London ranges
Velux / rooflight conversionNo structural change to the roof shape. Only possible where you already have the head height.
£25,000 – £45,000
Rear dormerThe most common London conversion. Adds head height and usable floor across the back of the roof.
£45,000 – £75,000
Hip-to-gable + rear dormerFor a semi or end-terrace with a hipped roof. Roughly 20–30% more usable space than a dormer alone.
£55,000 – £95,000
L-shaped dormerVictorian terraces with a back addition. Two dormers joined, so effectively two conversions.
£70,000 – £95,000
These are London figures for a full design-and-build, including the en-suite most people add. London labour runs roughly a third above the national average for loft work, which is why the same job costs noticeably less outside the M25.
What actually drives the price
- Head height. Under about 2.2m from the ceiling joists to the ridge and your options narrow to lowering the ceilings below or raising the roof. Both change the number significantly.
- Where the stairs go. The staircase has to land somewhere legal without wrecking the room below. On a narrow terrace this is often the hardest part of the whole design.
- Structural work. Steels, new floor joists and the padstones they bear on. Not optional, and priced from an engineer's calculations rather than a guess.
- The en-suite. Adding one means waste runs, a pump more often than not, and tanking. It is usually the single biggest optional cost.
- Roof condition. If the existing covering is at the end of its life, doing it while the scaffold is already up is far cheaper than revisiting it in three years.
Costs people forget to budget for
- Scaffolding for the duration, not for a fortnight.
- Structural engineer's calculations and building control fees.
- Party wall notices if you are on a terrace or semi — served two months ahead, so it sits on the critical path.
- Fire safety. A third storey triggers a protected escape route: fire doors to rooms off the stair and mains-wired interlinked alarms.
- Making good downstairs where the new staircase opening meets your existing landing.
Why we do not publish a fixed price
Because we would be guessing, and the guess would be wrong in your favour right up until it wasn't. Two identical-looking terraces can differ by £20,000 once you know where the stairs land and what the roof is carrying. We come out, measure the head height, work out what your roof will take, and give you an itemised written price before anything starts.
Ranges reflect commonly quoted London prices for 2026 and are given as guidance only — they are not a quotation, and they are not our prices for your job. More about our loft conversions →
