Loft Conversion Cost London 2026: How Much Does a Loft Conversion Cost?
- LCCL Construction
- Jun 29
- 3 min read
The cost of a loft conversion in London depends on the type of conversion, the size of the loft, the specification of finishes and the location within London. This guide gives you accurate 2026 loft conversion costs across all five conversion types so you can budget realistically before starting your project. LCCL Construction has delivered over 350 loft conversions across London and Hertfordshire and provides fully transparent pricing as part of our complete design and build service.
Loft Conversion Cost by Type in London in 2026
Velux loft conversion cost: £18,000 to £48,000. The most affordable option. Installs roof windows without altering the roof structure. Requires minimum 2.2m headroom. See our full Velux loft conversion guide.
Dormer loft conversion cost: £45,000 to £68,000. The most popular conversion in London. Creates a full-height room with vertical walls. See our full dormer loft conversion guide.
L-shaped loft conversion cost: £48,000 to £85,000. Best for terraced houses with a back addition — creates two bedrooms instead of one. See our full L-shaped loft conversion guide.
Hip to gable loft conversion cost: £47,000 to £78,000. Best for semi-detached and detached properties with a hipped roof. See our full hip to gable loft conversion guide.
Mansard loft conversion cost: £62,000 to £165,000. Creates the most floor space. Best for premium London locations. See our full mansard loft conversion guide.
What Is Included in a Loft Conversion Cost in London?
LCCL Construction's loft conversion costs include the full design and build service: measured building survey, architectural design, planning permission application where required, building regulations, structural engineer calculations, party wall notices and agreements where required, all construction works including roof alterations, structural steelwork, insulation, internal walls, staircase, electrics, plumbing and plastering. Decoration and fitted furniture are additional.
What Factors Affect Loft Conversion Cost in London?
The key factors are: type of conversion, size of the loft space, number of rooms and bathrooms, specification of windows and glazing, whether planning permission is required, complexity of structural works, location within London and quality of finishes. Premium London postcodes typically cost 10-20 per cent more than outer London due to higher labour costs, access constraints and planning complexity.
Loft Conversion Cost Per Square Metre in London
Loft conversion costs in London typically range from £1,200 to £2,500 per square metre of new floor space created.
A standard dormer creating 25 square metres at £1,800 per square metre costs approximately £45,000.
A premium mansard in a Central London conservation area creating 35 square metres at £3,500 per square metre costs approximately £122,500.
The cost per square metre is generally lower for larger conversions and higher for smaller or more complex ones.
How Much Value Does a Loft Conversion Add Compared to Its Cost?
A well-executed loft conversion in London typically generates a return of 150 to 300 per cent of the construction cost in added property value.
A dormer costing £55,000 typically adds £100,000 to £150,000 in value.
A mansard costing £90,000 in Knightsbridge or Mayfair can add £400,000 to £800,000.
See our full guide on how much value a loft conversion adds.
Frequently Asked Questions About Loft Conversion Costs in London
How much does a loft conversion cost in London in 2026?
From £18,000 for a Velux to £165,000 for a high specification mansard in a premium London location. A typical dormer with en-suite costs £45,000 to £68,000.
Does the cost include planning permission?
Yes — LCCL Construction includes all planning permission costs and professional fees in the design and build estimate.
What is the cheapest type of loft conversion?
A Velux loft conversion is the most affordable at £18,000 to £48,000 — but requires sufficient existing roof height of at least 2.2 metres.
To get a free detailed estimate call LCCL Construction on 020 8037 7332 or get an instant quote online.
