For millions of London homeowners, extending the family home is a far more financially sensible and practically attractive alternative to the disruptive, expensive, and uncertain process of moving to a larger property. With London’s stamp duty costs, estate agent fees, conveyancing costs, and removal expenses regularly totalling tens of thousands of pounds on a single house move, the case for investing that money into extending and improving the property you already own has never been more compelling.
A well-designed and professionally built house extension does far more than simply add square footage. It fundamentally transforms the way a family uses and experiences their home, whether that means creating an open-plan kitchen and dining space that becomes the heart of family life, adding a dedicated home office that genuinely separates work from living, building a spacious ground-floor bedroom suite for an elderly relative, or simply freeing the existing ground floor from the cramped, chopped-up layout typical of many Victorian and Edwardian London terrace houses.
MayfairMarketplace.uk connects London homeowners with experienced, vetted, and accredited building contractors who specialise in residential house extensions. Our listed builders cover every extension type across all London boroughs, from compact single-storey kitchen extensions to ambitious double-storey side and rear additions that dramatically increase both the living space and the market value of a property.
Extension Types Available in London
Understanding the different extension options available to your specific property type is the critical first step in any project planning process. Our listed builders can advise authoritatively on which extension types are feasible, permitted, and most cost-effective for your individual home:
Single-Storey Rear Extensions
The most common extension type in London. A single-storey rear extension projects from the rear elevation of the property, typically into the existing garden space, and most commonly creates a new or enlarged kitchen, dining room, or open-plan living space. Under Permitted Development Rights, most houses in London can extend up to six metres to the rear (terraced and semi-detached) or eight metres (detached) without requiring full planning permission, subject to the Neighbour Consultation Scheme.
Double-Storey Rear Extensions
A double-storey rear extension provides significantly more additional floor space by extending both the ground floor and the first floor simultaneously. This typically creates new kitchen and dining space on the ground floor whilst simultaneously adding one or two additional bedrooms or a substantially enlarged bathroom suite on the first floor. Double-storey extensions generally require full planning permission and a more complex structural engineering and architectural design process.
Single-Storey Side Return Extensions
Many Victorian and Edwardian London terrace houses have a narrow, underutilised side passage running alongside the kitchen, the side return. Infilling this side return with a glazed extension is one of the most transformative alterations possible on this property type, creating wide, light-filled open-plan kitchen and dining spaces that feel entirely contemporary despite the age of the original house. Side return extensions are subject to planning permission in most cases.
Wrap-Around Extensions
A wrap-around extension combines a rear extension and a side return extension into a single, cohesive L-shaped addition. This approach maximises the additional floor space created in a single construction phase and produces some of the most dramatic interior transformations available to London terrace house owners.
Over-Structure Extensions
In some London properties, it is possible to build above an existing flat-roofed garage, utility room, or single-storey section of the house, adding a new room at first-floor level without requiring any ground-level garden space. These projects require careful structural assessment but can provide excellent additional space with minimal external footprint.
Planning Permission and Permitted Development in London
Navigating the planning system is one of the most important and frequently misunderstood aspects of any London extension project. Your builder and architect will advise you specifically on your property’s planning position, but the key principles are as follows:
Many single-storey rear extensions fall within Permitted Development Rights and do not require a formal planning application, although properties in Conservation Areas, Article 4 Directions, or those that are Listed Buildings will have significantly more restricted Permitted Development Rights and will almost always require full planning consent.
All extensions that fall outside Permitted Development parameters require a formal planning application to your local London borough council, which typically takes eight to ten weeks to determine.
Regardless of whether planning permission is required, all residential extensions in London require Building Regulations approval, which ensures the structural integrity, fire safety, thermal performance, and electrical and drainage compliance of the completed work. Your builder will manage this process on your behalf.
How Much Does a House Extension Cost in London?
Extension costs in London are higher than the national average, reflecting the capital’s higher labour costs, higher material delivery costs, and frequently more complex site conditions. As a general guide:
- A single-storey rear extension of 20 to 30 square metres typically costs between £45,000 and £90,000 in London, depending on specification and finish quality.
- A double-storey rear extension costs proportionally more, typically ranging from £80,000 to £160,000 for a mid-range specification.
- A side return extension typically costs between £40,000 and £80,000 depending on length and glazing specification.
These figures are indicative only. Your builder will provide a detailed, itemised quotation following a thorough site survey.
Frequently Asked Questions
The construction phase for a single-storey rear extension typically takes between eight and fourteen weeks from groundworks commencement to practical completion. A double-storey extension may take between sixteen and twenty-four weeks. The pre-construction phase, including architectural design, planning application, structural engineering, and procurement, typically adds a further three to six months before construction begins.
For all but the most straightforward extensions, instructing an architect or architectural designer is strongly recommended. A good architect will maximise the use of space within your extension, navigate the planning system effectively, and produce detailed construction drawings that enable your builder to price the work accurately and build it correctly. Many experienced builders work with preferred architectural practices and can recommend a suitable designer.
A well-designed and well-built extension almost invariably adds significant value to a London property. A high-quality open-plan kitchen extension on a London terrace house, for example, can add between 10% and 15% to the property’s market value, frequently representing a return that exceeds the cost of the extension itself.
Get a Free Extension Quote in London
Ready to transform your London home? Use MayfairMarketplace.uk to find an experienced, trustworthy house extension builder in your borough. Submit your enquiry today with a brief description of your project, and we will connect you with a vetted local builder who can provide a free, no-obligation site survey and quotation.