Loft Conversion Cost London 2025 — What You Really Pay
Detailed 2025 cost breakdown for every type of loft conversion in London — Velux, dormer, hip-to-gable, mansard and L-shaped. Real prices, not estimates.
Loft Conversion Costs in London 2025
A loft conversion is consistently one of the best-value improvements you can make to a London home — adding between one and two bedrooms without reducing garden space. But costs vary significantly based on the type and specification.
Velux / Rooflight Conversion: £20,000–£35,000
The simplest and most affordable option. New Velux or equivalent roof windows are inserted into the existing roof slope without altering the roofline. No structural changes to the ridge or eaves. Cost is lower but headroom is limited — the conversion is only viable if the existing roof pitch creates at least 2.2m of usable height.
Includes: Velux windows, new stair, floor joists, insulation, plasterboard, electrics, decoration. Does not typically include en-suite (add £8,000–£15,000).
Dormer Conversion: £45,000–£70,000
The most popular loft conversion type across London. A box-shaped structure projects out from the rear roof slope — creating vertical walls and maximising usable floor area. Works well on Victorian and Edwardian terraces.
Includes: all structural steelwork, new floor joists, dormered roof structure, flat roof (GRP or zinc), windows, new stair, full internal fit-out, and decoration. En-suite bathroom included in most packages.
Hip-to-Gable Conversion: £55,000–£85,000
Suitable for semi-detached or detached houses with a hipped roof. One or both hipped ends are extended to create a full gable wall — significantly increasing floor area. Often combined with a rear dormer.
L-Shaped Dormer: £55,000–£90,000
A dormer that wraps around both the rear and side of the property. Common on Victorian terraces in South and East London. Creates the maximum possible floor area within the existing footprint.
Mansard Conversion: £65,000–£100,000
The most extensive conversion — the rear (or both front and rear) roofslopes are raised to near-vertical, with a small flat section at the top. Maximum headroom and floor area. Often the only viable option for deeper floor plans.
What Drives Costs Up
Party wall awards (mandatory for terraced and semi-detached properties), structural engineer fees, the complexity of the internal layout, and the specification of the en-suite bathroom are the key variables. Zinc or copper roof coverings add a premium over standard GRP.
Call SuperBuilder on 0800 530 0853 for a free loft conversion survey.
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