Costs · Extensions
What Affects the Cost of a Loft Conversion in London
Loft costs depend heavily on the type of conversion and the work it triggers elsewhere in the house. This guide sets out the main cost drivers, without quoting a headline figure.
The type of conversion matters most
A rooflight conversion within the existing roof, a rear dormer, a hip-to-gable and a full mansard are very different in cost, because they involve very different amounts of new structure and roof alteration. The more the roof is reshaped, the more the cost — but also, usually, the more usable the space.
Our fixed-fee packages
Design fees, inc. VAT — separate from the council fees above
| Package | Fixed fee |
|---|---|
| Planning Route ReviewA paid route check before drawings or applications. | £395 inc. VAT |
| Standard Planning Drawings PackageFor straightforward householder schemes. | from £1,450–£1,950 inc. VAT |
| Full Householder Planning PackageDrawings plus application preparation and submission. | from £2,250–£3,250 inc. VAT |
| Licence to Alter / Flat Refurbishment Drawing PackLeasehold flat alterations and freeholder consent drawings. | from £1,500–£2,750 inc. VAT |
| Building Regulations / Technical Drawing PackageTechnical drawings once the planning route is clear. | from £2,750–£4,950 inc. VAT |
| Listed / Conservation Planning PackHeritage-led drawings and consent strategy. | Quoted after review |
Fixed fees quoted before you commit, credited from the £395 route review if you proceed. Larger, listed or complex projects are quoted after a paid review rather than sold at a fixed price. See all packages or find your package.
Structure, stairs and fire safety
A loft conversion is rarely just work in the loft. New structure is needed to carry the floor, a compliant staircase has to be fitted in (which can affect the floor below), and adding a storey changes the means of escape for the whole house — usually triggering a protected stair, fire doors and detection. These knock-on works are a significant part of the cost and are easy to underestimate.
Planning and conservation
Where planning permission is required — common in conservation areas and for dormers and mansards — there are application fees and a longer programme, and conservation constraints can require more expensive materials and detailing. A mansard in a sensitive area is both the most generous and the most demanding option.
Finishes and bathrooms
As with any project, the specification drives cost: an ensuite bathroom (with its plumbing and waterproofing), built-in storage to use the awkward roof geometry, rooflights and the quality of finishes all add to the figure. Lofts often need clever joinery to be genuinely usable, which is worth budgeting for.
Getting to a real number
A reliable cost comes from a design that resolves the structure, stairs and fire strategy, and a competitive tender. We prepare the drawings that let contractors price the same scope, so the quote reflects the real work rather than optimistic assumptions.
Frequently asked questions
Why does a loft conversion cost more than just the loft?
Is a mansard more expensive than a dormer?
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Related services and areas
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