Understanding the Different Types of Home Extensions

Homeowners in London often look to extend their house rather than move, making the most of limited urban space. Common approaches include adding ground-floor extensions, building up or down, or repurposing under-used lofts. Each extension type has its own advantages and challenges. Below we explain the main options – single-storey rear, side-return, wrap-around, double-storey, loft and basement conversions – with notes on how they suit London’s houses, planning rules and space constraints.

Single-Storey Rear Extensions

A single-storey rear extension (ground-floor addition to the back of the house) creates extra living space, often for a larger kitchen, dining area or family room. It typically features large sliding or bi-fold doors onto the garden. In London terraces, small rear extensions (around 3 m deep) usually fall under Permitted Development rights, meaning no full planning application is needed if limits aren’t exceeded. These extensions are popular for open-plan layouts and bringing in daylight. However, they also reduce garden space and may need planning approval if very deep. Key points for homeowners:

• What it adds: Much more open-plan living area (e.g. a kitchen/diner or extra lounge)‍. Rooflights or lanterns can boost natural light.
• London context: Common on Victorian/Edwardian terraces. Permitted Development usually allows up to ~3 m rear projection (double with a prior-notification scheme). A Party Wall Agreement is often needed because walls are shared.
• Considerations: Loss of outdoor garden/deck space, structural work for foundations, and possible impact on neighbours’ daylight. Very large extensions require full planning permission and Building Regulations approval.

Side Return Extensions

A side-return extension builds into the narrow alley (side passage) next to a terraced or semi-detached house. This “side gap” space is often under-used, and extending into it can dramatically widen a tight kitchen or living area. Adding a rooflight or glazed roof can flood the room with light. London’s row houses often have this alley space, making side returns very common. Benefits and cautions include:

• Advantages: Makes use of wasted side space (useful on narrow plots). Ideal for terraces and semi-detached homes. It adds width to ground-floor rooms and often brings in extra daylight (via skylights or glass roofs). Because it’s usually single-storey and modest in size, it may be easier to approve under Permitted Development than a deep rear extension.
• Challenges: Limited width means careful furniture layout is needed. Work often involves opening or rebuilding the existing side wall (structural support is needed). This type is not applicable if the house has no side passage (e.g. detached or wide-fronted homes). Planning permission may still be required, especially if extending more than a few metres or in conservation areas.

Wraparound Extensions

A wraparound (L-shaped) extension combines a rear extension with a side-return build, essentially “wrapping” new space around the back corner of the home. This creates a very large, open-plan ground floor and can have a striking contemporary look. It works especially well on period terraced or semi-detached houses with an existing side return, as noted by architects: “Wrap around extensions typically work best on Victorian and Edwardian terraced and semi-detached homes”. Key points:

• Advantages: Maximises floor area by using both rear and side land. It transforms the flow of a traditional house into a modern, open-plan layout, often with more natural light and architectural interest (angled walls or rooflights). When well-designed, it gives a “wow” factor and can greatly improve how the home feels.
• Challenges: This is a complex build. A wraparound is typically more expensive and technically involved than a simple rear or side extension. It usually requires full planning permission (beyond Permitted Development limits). Designers must take care to avoid creating dark zones – e.g. central corridors with no daylight – and to prevent overshadowing neighbours’ gardens. Underground services and party walls can complicate construction. In conservation areas or tight urban plots, planning hurdles (and costs) can be significant.

Double-Storey Extensions

A double-storey extension adds two floors of new space (one on top of another). For example, you might build a single-storey extension and then construct a new first floor over it. This approach effectively adds an extra bedroom or bathroom upstairs while enlarging the living area below. It’s ideal for homeowners who want a substantial increase in space without expanding the building’s footprint. Advantages and trade-offs:

• Advantages: Adds a large amount of space for family use – e.g. additional bedrooms or a larger master suite above, plus a bigger kitchen or living area below. Because a rear double-storey extension retains the original front façade, it is often more acceptable to planners. (As Urbanist Architecture notes, it “won’t change your house’s facade, which will normally please the council”.) This can result in a neat, balanced layout, since many houses are wider than they are deep. Double-storey extensions make creative reconfiguration of the home possible while keeping the garden largely intact.
• Challenges: This is a major project. Costs and disruption are significantly higher than a single-storey addition. A deeper foundation and stronger structure are required, and the build time is longer. Importantly, double-storey extensions almost always need full planning permission (Permitted Development rights generally do not cover two-storey builds). Neighbours may be more affected by loss of light or privacy on the second floor. In short, careful planning and design are needed to ensure a good result.

Loft Conversions

In London’s older housing stock, loft or attic space often goes unused – especially in Victorian and Edwardian homes with steep roofs. Converting the loft is a popular way to gain a new bedroom, home office or studio without altering the garden at all. A well-designed loft can effectively add a new floor of living space. Loft conversions are very common in urban areas (where garden space is tight), since they give extra space “without needing to move house”. Advantages and considerations include:

• Advantages: Significant extra space – often a whole new bedroom and possibly an ensuite bathroom or study. The work is mostly internal, so it can often proceed under Permitted Development rules (as long as volume and height limits are respected). Many London conversions use dormer windows or rooflights to bring in daylight, making the space bright. Because you’re working within the existing roof structure, the garden remains untouched. This is a very efficient way to expand a family home.
• Challenges: The existing roof must have enough headroom; sometimes the roof shape must be altered or raised (especially for mansard or full-width dormers). You’ll need a new staircase and must meet fire-safety and insulation requirements. In conservation areas, visible roof alterations can be restricted. (Typically, a simple Velux-style conversion with windows flush to the roof slope is allowed by right, but larger dormers or mansard conversions may need planning permission.) In short, structural modifications and regulatory compliance (Building Regulations, Party Wall agreements) are key factors.

Basement Conversions

Many older London houses (especially Georgian, Victorian and Edwardian terraces) already have a basement or cellar. Converting this space can add a substantial new room or even multiple rooms below ground – for example a guest suite, home cinema, gym or office. Modern conversions use waterproofing, insulation and clever lighting (light wells, windows or even walk-on glass panels) to make basements feel usable and bright. Because the extra space is “hidden” underground, it avoids shrinking the garden or altering the house footprint. Some key points:

• Advantages: Unlocks “hidden” space. In terraced London houses that have basements, conversion can dramatically increase usable area without any change to the street view. It’s often a practical solution where external space is very limited (for many inner-London homes, it’s hard to extend outwards due to tight plots or planning restrictions). A modern basement can be designed as a seamless, light-filled room under the floor above. (For example, well-placed windows in light wells or a sunken patio can bring daylight downstairs.) The result is a flexible new living area that integrates with the rest of the home.
• Challenges: Converting a basement is technically demanding and can be expensive. If a basement already exists, you mainly need to excavate floor, install drainage/waterproofing and fit services. If no basement exists and one must be dug out, that involves major excavation, underpinning foundations and relocating utilities – a very large undertaking. London’s high water table in parts of the city can make new basements tricky. Careful structural engineering and a Party Wall survey (if houses are attached) are crucial. In many cases, internal conversions alone may not need planning permission, but adding new front windows, lightwells or external stairs does trigger approval.

Each extension type offers different benefits for London homes. A rear or side extension quickly adds more ground-floor living space, wrap-arounds maximise both dimensions for airy layouts, a double-storey adds vertical space for bedrooms, loft conversions open up unused roof space, and basements utilise the underground potential. The right choice depends on your home’s style (terraced, semi, detached), available land, and planning constraints. Always consider factors like natural light, party walls and local planning policies. Consulting an architect or extension specialist can help ensure your new addition both meets your needs and fits London’s unique context.

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