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The most popular London extension type. Opens up the ground floor with a kitchen-diner, adding space and value to terraces and semis.
Get quotes →Adds space on both floors simultaneously. Typically more cost-effective per square metre than building two separate single-storey projects.
Get quotes →Fills the narrow side passage common in Victorian terraces to create a wider, brighter kitchen or dining room. Very popular in inner London.
Get quotes →Combines a rear and side return extension for maximum ground floor space. Transforms the layout of Victorian terrace houses.
Get quotes →Open-plan kitchen, dining and living space extending from the rear. The most sought-after layout for London family homes.
Get quotes →Glazed roof lanterns, bifold doors and structural glass bring the outside in. Popular for kitchen extensions across all London boroughs.
Get quotes →| Job | Low estimate | High estimate |
|---|---|---|
| Single-storey rear extension | £25,000 | £50,000 |
| Double-storey extension | £45,000 | £90,000 |
| Side return extension | £20,000 | £40,000 |
| Wrap-around extension | £35,000 | £70,000 |
| Kitchen-diner (open plan) | £30,000 | £60,000 |
| Structural engineer fees | £1,500 | £3,000 |
| Architect fees | £3,000 | £8,000 |
| Planning application fee (householder) | £206 | £206 |
| Party wall agreement (per neighbour) | £700 | £2,000 |
| Lawful Development Certificate | £103 | £206 |
Prices are estimates for London 2026. Costs vary by specification, borough, ground conditions, and access. Always get multiple quotes.
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House extensions are the most popular home improvement project in London. With property prices at a premium and moving costs — stamp duty, legal fees, estate agents — significant, extending an existing home almost always makes better financial sense than upsizing. A well-designed single-storey rear extension adds 10–15 square metres to a Victorian terrace, transforming a cramped back room into an open-plan kitchen-diner that modern buyers expect. Double-storey extensions add space on both floors simultaneously and are more cost-effective per square metre than two separate projects. Side return extensions are particularly popular in inner London's Victorian terraces, using the narrow side passage to widen the kitchen without touching the rear garden.
Permitted Development rights allow many London homeowners to build single-storey rear extensions without a planning application, provided the extension stays within national size limits. However, conservation areas, Article 4 Directions, and listed buildings can remove these rights — and London has more conservation areas per square kilometre than almost any other UK city. Always confirm your planning position before commissioning architects or builders. If your extension requires planning permission, the standard 8-week decision period applies, though pre-application advice from the council can significantly reduce the risk of refusal.
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