How much does a loft conversion cost in the UK?
A loft conversion typically costs between £25,000 and £100,000+ in the UK, depending on the type of conversion, the size of the space and where you live. London costs run 20–30% higher than the national average due to labour rates, access constraints and the complexity of working in densely built Victorian and Edwardian streets.
This guide breaks down the costs by conversion type, explains what drives the price up or down, and helps you understand what a realistic budget looks like before you speak to a builder.
If you're based in London and ready to take the next step, see our loft conversions page for details on how Beams can help.
Loft conversion costs by type
The type of conversion is the single biggest factor in your final cost. Here is a breakdown of typical UK costs and London costs by conversion type.
Velux / rooflight conversion
The simplest and most affordable option. No changes to the roof structure — Velux or rooflight windows are installed into the existing roof slope. Works best where there is already sufficient head height (at least 2.2 metres from floor joist to ridge).
UK cost: £20,000–£40,000
London cost: £25,000–£45,000
Dormer loft conversion
The most popular choice for London terraced houses. A box-shaped extension is added to the rear roof slope, creating full-height usable space — typically enough for a bedroom and en suite. Requires planning notification but usually falls under Permitted Development.
UK cost: £35,000–£60,000
London cost: £45,000–£75,000
L-shaped dormer
A rear dormer combined with a second dormer over the back addition — common in Victorian terraces with outriggers. Can add two bedrooms and a bathroom. More expensive than a standard dormer due to the additional structure.
UK cost: £45,000–£70,000
London cost: £55,000–£85,000
Hip-to-gable conversion
Suited to semi-detached and end-of-terrace homes with hipped roofs. The sloping hip is replaced with a vertical gable end, usually combined with a rear dormer. More structural work than a dormer, but creates significantly more space.
UK cost: £45,000–£65,000
London cost: £55,000–£75,000
Mansard conversion
Maximum space — near-vertical walls and a flat roof create an almost full-storey addition. Common in conservation areas and period properties. Almost always requires full planning permission. The most expensive conversion type.
UK cost: £55,000–£80,000
London cost: £70,000–£100,000+
All figures are indicative ranges excluding VAT, professional fees and interior fit-out. Your builder will confirm a fixed price for your specific project before any commitment is made.
What affects the cost of a loft conversion?
Beyond the type of conversion, several factors can push costs higher or lower.
Size of the space
Larger loft spaces cost more to convert. More floor area means more structural work, more insulation, more electrics and more finishing. A 20 sqm dormer conversion will cost significantly less than a 40 sqm one.
Roof structure
Older cut roofs — common in Victorian and Edwardian properties — are generally more straightforward to convert. Modern trussed roofs require more structural work to create usable space, which adds cost.
Staircase
A new staircase is always required and can be expensive depending on the design and available space. A simple straight staircase costs less than a bespoke spiral or space-saving design. Budget £3,000–£10,000 for a well-designed staircase.
Bathroom or en suite
Adding a bathroom to the loft adds plumbing, tiling and sanitary-ware costs. A basic en suite typically adds £5,000–£12,000 to the project.
Structural work
Steel beams are commonly required in loft conversions to support the new floor structure. Expect to pay £2,000–£5,000 for steelwork, depending on span and complexity.
Access and location
In London, tight streets, restricted parking for skips and deliveries, and limited working hours in some boroughs all add to labour costs. Properties in conservation areas may also require specific materials, which can be more expensive.
Finish specification
The level of finish — flooring, lighting, joinery, bathroom specification — has a significant impact on final cost. A basic functional finish will cost less than a high-specification one with bespoke storage, underfloor heating and premium tiles.
What is not included in loft conversion quotes
When comparing quotes, make sure you understand what is and is not included. Common exclusions:
- VAT — most builders quote excluding VAT. Add 20% to any net figure.
- Architect or structural engineer fees — typically £1,500–£5,000 depending on the scope of design work required.
- Party Wall surveyor fees — if the Party Wall Act applies (as it often does in London terraces), budget £1,000–£3,000 for surveyor fees.
- Planning application fees — if planning permission is required, the fee is currently £258 for a householder application in England.
- Lawful Development Certificate — recommended even where planning is not required. Around £103 to apply for.
- Interior fit-out — flooring, decoration, furniture and storage are often excluded from the structural quote. Budget separately for these.
Is a loft conversion worth the money?
In most cases, yes — particularly in London.
A well-executed loft conversion typically adds 15–25% to a London property's value. On a £600,000 home, that could mean £90,000–£150,000 of added value from a project costing £50,000–£75,000.
Compare that to moving house. Stamp duty alone on a £750,000 London property is £27,500, and total moving costs in London regularly exceed £40,000 — before the disruption of uprooting your family and leaving your neighbourhood.
A loft conversion creates the space you need, in the home you already love.
For a full guide to planning your loft conversion — including permitted development rules, party wall advice and how to find the right builder — see our guide to how to plan a loft conversion in the UK [LINK: /blog/how-to-plan-a-loft-conversion-uk].
How to get an accurate loft conversion cost
The only way to get a reliable cost for your specific project is to have a builder visit the property, assess the roof structure, head height and access, and produce a detailed fixed-price quote.
Beams matches London homeowners with vetted builders who specialise in loft conversions. You receive up to three like-for-like quotes, so you can compare on a fair basis before committing to anything.
Know what your loft conversion should cost and how long it should take
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