Side Extension vs Rear Extension — Which Is Right for Your Home?

Introduction

Many homeowners planning a ground-floor extension face an early choice: extend to the rear, to the side, or potentially a combination of both. The right answer depends on a mix of factors — the size and shape of your plot, what planning policy allows, what your house needs most, and what your budget is.

This guide walks through the key differences to help you think clearly about which direction is right for your project.

Rear Extensions

A rear extension adds space behind the main back wall of your home. It's the most common type of ground-floor extension in London, and for most Victorian and Edwardian terraced houses, it's the primary option because there's no side space available.

Permitted Development. Single-storey rear extensions under 3m (for terraces and semis) or 4m (for detached houses) can often be built under Permitted Development rights, avoiding the need for planning permission — though prior notification under the Neighbour Consultation Scheme may still be required up to 6m and 8m respectively.

What it typically adds. Rear extensions usually expand the kitchen, create an open-plan kitchen-diner, add a garden room or family room, or relocate the kitchen to create a more useful layout.

Design considerations. The depth of the extension is constrained by planning policy and the depth of the rear garden (you need to leave usable outdoor space). Glazing to the rear — roof lights, bifold or sliding doors — is important for light penetration.

Side Extensions

A side extension adds space to the side of the house, typically using the side passage or alley, or extending into the side of the garden. These are more common on semi-detached and detached houses where a side flank is accessible.

Planning requirements. Side extensions almost always require planning permission, because Permitted Development rights for side extensions are more limited — the extension must not exceed half the width of the original house, must not be forward of the principal elevation, and must not include a first-floor extension above the side.

What it typically adds. Side extensions can add a utility room, extended hallway and cloakroom, or additional reception space. They can also create a larger kitchen by expanding sideways rather than backwards.

Design considerations. A side extension next to a shared boundary may trigger the Party Wall Act, requiring a party wall agreement with the neighbouring owner. This is particularly relevant where the extension involves any excavation close to the party wall.

Wrap-Around Extensions — The Best of Both

Where a property has both rear garden space and a usable side, a wrap-around extension combining rear and side elements can deliver a significantly more spacious and functional ground floor than either alone.

A wrap-around extension typically involves a rear extension of the back wall combined with a side infill of the passage, creating an L-shaped footprint that improves both depth and width. The result is often a much more generous kitchen-dining-living space than a rear extension alone could achieve.

Wrap-around extensions typically require planning permission for the side element, and often for the whole scheme. They involve more complex structural and drainage co-ordination than a straightforward rear extension.

Key Questions to Ask

When deciding which approach suits your home:

What does your plot allow? Is there a usable side space? Is there enough rear garden depth to extend backwards and still have usable outdoor space?

What does planning allow? Is your property in a conservation area or under an Article 4 direction that removes Permitted Development rights? What has been approved on comparable properties in your street?

What does your home most need? Is your kitchen the main priority, or are you trying to create additional reception space or a utility room?

What is your budget? Side extensions and wrap-arounds are generally more expensive per square metre than straightforward rear extensions because of their structural complexity and planning requirements.

Not sure which direction is right for your project?
RCB Design & Build provides design and build advice from early concept through to delivered project. Contact us to discuss your options.