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Rear extensions — the most common approach in Chelsea, typically extending the kitchen or living space into the garden. Often combined with bifold or crittall-style glazing to bring in natural light while keeping the front elevation untouched.
Side return extensions — infilling the side alley space common on Victorian terraces, usually to widen a kitchen-diner. A cost-effective way to add meaningful space without a full rear extension.
Double-storey extensions — extending at both ground and first floor, typically used to add an extra bedroom or bathroom above an extended kitchen below. More involved structurally, and more likely to require full planning permission given the additional roofline impact.
Several factors set the final cost of a house extension in Chelsea:
Size and layout — footprint, number of storeys, and structural complexity Type of extension — rear, side return, wraparound, or double-storey Materials and finishes — brick matching, glazing specification, roofing Planning requirements — full planning permission is the norm in Chelsea's conservation areas, adding both time and design cost Site access — narrow terraced streets often mean higher labour and logistics costs than outer London.
Rear extensions in Chelsea typically run £80,000 to £200,000; side return conversions from £50,000 to £100,000; double-storey extensions £150,000 to £300,000, depending on specification.
Contact us today to discuss your house extension project in Chelsea and get a free no obligation quote. Our team is ready to provide you with expert advice and tailored solutions. Let us help you create a space that meets your needs and exceeds your expectations.
Conversion type | What it involves | Typical cost |
Roof light (Velux) | Skylight windows added to the existing roof, no structural change | £25,000 – £50,000 |
Dormer | Box-shaped extension to the rear roof slope, adds standing height | £45,000 – £70,000 |
Hip-to-gable | Converts a sloping hip roof into a vertical gable wall, common on semi-detached properties | £45,000 – £70,000 |
Mansard | Replaces most of the roof slope with a near-vertical wall, maximises space | £60,000 – £100,000 |
L-shaped dormer | Combines a rear dormer with a side extension over the back addition | £50,000 – £80,000 |
Project type | Description | Typical cost |
Basic conversion | Existing basement converted to a habitable room, no excavation | £100,000 – £200,000 |
Full excavation | No existing basement, or excavation needed to increase ceiling height | £250,000 – £500,000 |
Double-level basement | Extensive excavation and underpinning for maximum added space | £500,000+ |
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The most affordable option, a Velux conversion, adds skylight windows to your existing roof without major structural changes.
This option transforms a sloping “hip” roof into a vertical “gable” wall, maximising space in semi-detached properties..
A more complex project, a double-level basement adds significant space to your property but requires extensive excavation, underpinning, and design expertise.
Ideal for period properties or those in conservation areas, a Mansard conversion significantly alters the roof’s structure to add the most space.
Perfect for Victorian or period properties, this extension maximises space by extending both the rear and side roofs.
Several elements can impact the overall price of a loft conversion, including:
Contact us now for a free consultation to discuss your loft conversion project in Chelsea.