Quick Summary
Side return extensions typically take 3–5 months to complete and cost between £80,000 and £200,000, depending on size and design. Smaller single-storey projects are around 3m × 5m, while larger double-storey extensions can be taller and wider. Planning permissions, party wall agreements, and neighbour consultations can affect timelines and costs, but these estimates cover most straightforward projects.
Side return extensions are among the most popular ways to improve a home. They make use of unused space along the side of a property, enhance natural light, and are usually faster and less expensive to build than other types of extensions. These extensions are highly versatile, offering homeowners plenty of options for how to use the extra space.
What Is a Side Extension?
A side return extension involves building in the unused space alongside a property. Common types include:
- Single-storey side extension (approx. 3m × 5m, £90K–£120K)
Adds ground floor living space by utilising the side area of a property. - Double-storey side extension (approx. 2m × 7m, £150K–£200K)
Expands the property over two floors, creating significant additional living space. - Side kitchen extension (approx. £80K–£120K)
Extends the kitchen into unused side space, enabling a modern, open-plan layout. - Victorian terrace side extension (approx. £80K–£120K)
Ideal for Victorian homes with narrow side alleys, allowing for an expanded layout. - Glass side extension (approx. £80K–£140K)
Maximises natural light with large glass panels, skylights, or sliding doors.
These estimates are approximate. For a tailored calculation, use our Quick Quote Calculator.
Do You Need an Architect?
If your project affects the exterior of your home, hiring an architect is highly recommended. Architects ensure that your extension is safe, legal, and aesthetically pleasing, and help avoid unexpected issues during construction. Learn more about what an architect can do for your extension project.
Space Requirements for a Side Extension
One key benefit of side extensions is that they take up minimal space. Unlike rear extensions, side extensions typically utilise unused side areas between properties, preserving garden space.
Planning Permission for a Side Extension
Many side extensions can be completed under permitted development rights, avoiding full planning permission. Key considerations include:
- Located at the side of the property (not front-facing a road)
- Matches existing building materials
- Occupies less than 50% of land around the property
- Less than 50% of the original house width
- Height under 4m (or 3m if within 2m of a boundary)
- Eaves and ridge no taller than the existing house
If you’re unsure whether your project qualifies, schedule a free consultation with our experts.
Party Wall Agreements
Side extensions may affect shared walls with neighbouring properties, known as party walls.
- If your project involves a party wall or excavation within 3–6m of a neighbour’s property, you must obtain permission at least 2 months in advance.
- Consult a surveyor to check property lines and avoid potential legal or repair costs.
Book a free advice session with one of our consultants to ensure compliance.
Construction Timeline
Side extensions typically take 3–5 months to complete. Experienced architects and contractors can help streamline the process and keep your project on track.
Is a Side Extension Worth It?
Side extensions are a practical solution for homeowners with unused side space. Benefits include:
- More living space: Perfect for open-plan kitchens, additional bedrooms, or storage.
- Increased natural light: Incorporate glass panels, skylights, or sliding doors to brighten interiors.
- Flexible design: Suitable for Victorian terraces, modern homes, or any property layout.
Finding Vetted Builders Through NABC
For peace of mind, consider hiring vetted builders by NABC. Every builder in our network is fully vetted for reliability, quality, and compliance with building regulations. This ensures your side extension project is carried out safely, efficiently, and to a professional standard.
Using an NABC-approved builder can save time, reduce stress, and help avoid common pitfalls with construction, planning, or neighbour disputes. Find your trusted local builder through www.nabc.org.uk.