Side return extensions in London

What is a side return extension?

Side return extensions are a popular way of increasing the size of Victorian and Edwardian houses in London. These properties often feature an original rear extension or ‘outrigger’ behind the main house, typically of two storeys underneath a pitched roof.

The rear outrigger occupies only part of the width of the plot to allow light into the rear reception rooms in the main part of the house. This creates a leftover space, a narrow and shaded part of the garden that is usually hard-paved and underused. A side return extension encloses this space and typically creates a new party wall along the boundary with the neighbouring house.

Architecture for London is an RIBA Chartered Practice. We design extensions, refurbishments and new homes, with particular experience in upgrading period properties to modern standards of comfort and energy performance. View our project portfolio, or if you would like to discuss your project, please contact us.

Side return extensions are particularly effective on terraced and semi-detached homes. Here, the use of the original external side passage is limited, but it does offer an opportunity to expand the kitchen and dining areas. They can be designed as modest infill additions or as more ambitious full-width rear extensions that completely transform the ground floor layout.

A well-designed side return extension will consider not only additional floor area, but also daylight, views to the garden, connection to outdoor space and improved circulation through the home. The aim is to turn a dark, cellular ground floor into a bright, flexible, open-plan living space.

Heart of the home

The new volume is often joined as one by inserting steel beams, allowing the removal of the original side wall. The kitchen can, therefore, be widened to become a generous space. It can be further enhanced by a glass box or glass sliding doors to the rear, creating improved views of the garden.

This can transform the kitchen into the social heart of the home. A side return extension frequently accommodates a family dining area, a breakfast bar or island, and built-in storage, helping to declutter the rest of the house. Underfloor heating, polished concrete or timber flooring, and carefully integrated lighting all contribute to a comfortable, contemporary space.

For families, this layout allows cooking, eating, homework and play to happen in one open plan space, with easy supervision of children in the garden. For those who enjoy entertaining, sliding or folding doors can open the full width of the extension, creating a seamless connection between inside and outside during warmer months.

Creating vertical space in a side return extension

Rear outriggers were originally designed to contain service spaces and typically have lower ceiling heights than the principal rooms of the house. These can be improved by lowering the kitchen floor by one or two steps to create a more generous volume. Alternatively, inventive double-height spaces or set-back mezzanines can be created by removing some or all of the floor above. These approaches create dramatic vertical space, something that is often missing from terraced properties.

Rooflights, high-level glazing and carefully positioned windows can emphasise this sense of height, washing internal walls with daylight and drawing the eye upwards. Exposed structure – such as steel beams or timber joists – can add character and texture, while also showing how the structure of the extension works.

Shared wall issues in London

Roof heights on the shared boundary wall are frequently limited for side return extensions. Local planning policy usually restricts these heights to reduce any impact on the neighbouring house, in terms of daylight and sense of enclosure. The particular requirements vary from borough to borough, yet they are usually set out in a residential design guide or supplementary planning document.

In addition to planning constraints, the Party Wall etc. Act 1996 often applies to side return extensions, as work will usually involve building on or close to the boundary. It is important to notify neighbours correctly and to agree any necessary party wall awards before construction begins.

Materials and details at the shared wall must be carefully considered for fire safety, weathering and acoustic performance. Good detailing can minimise sound transfer between properties and create a discreet, well-mannered elevation to the neighbouring side.

Daylight

A skylight or even an open light well is best placed to the rear of the new side return extension. This will allow as much natural light as possible in the original rear reception room.

A large skylight over the side return can create a striking, light-filled space alongside the original room. Where a more traditional appearance is desired, a series of smaller rooflights between structural rafters may be preferable to a single large pane.

Glazing to the garden, internal glazed screens and light-reflective finishes (such as light coloured joinery, polished concrete or limewash) all help to bring daylight deep into the plan. Where neighbouring windows limit the amount of side-facing glazing, borrowing light through internal windows and open-plan layouts becomes particularly important.

Planning and conservation

Many side return extensions can be built under permitted development rights, but in London these rights are often restricted, especially in conservation areas or for flats and maisonettes. Height, depth and materials may be controlled to preserve the character of the street and the setting of heritage assets.

Engaging an architect experienced with local planning authorities can help to navigate these constraints, ensuring that the extension is both policy-compliant and of high design quality. Early pre-application discussions with the council can also be beneficial when proposing a side return extension to a listed building in London.

Sustainability

A side return extension offers an opportunity to dramatically improve the thermal performance and comfort of period homes in London. High levels of insulation, airtightness measures, triple glazing and mechanical ventilation with heat recovery (MVHR) can be integrated into the new structure.

Works can be combined with sustainability upgrades to the existing house – such as wall insulation, improved roofs and floor insulation, and low-carbon heating systems. This approach can reduce energy use, improve indoor air quality and future-proof the property against rising energy costs.

Side return extensions in London: costs and construction

The cost of a side return extension varies depending on size, specification and complexity, but it is typically one of the most cost-effective ways to gain additional space in London. Structural alterations to remove existing walls, relocate drainage, or lower floors will influence the budget, as will the level of interior fit-out and joinery.

Construction usually requires temporary support to the existing rear wall, installation of new steelwork, formation of foundations and drainage, and then the building of the new external envelope and internal finishes. A well-planned programme and clear tender documentation help to keep costs under control and minimise disruption to the household.

Architecture for London is an RIBA Chartered Practice. View our project portfolio, or if you would like to discuss improvements to your property, please contact us.

Project architects: Ben Ridley, Tom Dawson, Amrit Marway