South London Extensions: Costs and Options in 2026
15, Jan, 2026
More homeowners across South London are choosing to extend instead of moving. Due to the rising property prices, limited housing stock, and the need to stay closer to schools, transport, and the community, an house extension is becoming the new norm for modern families.
However, not all extensions are designed for every property. Victorian terraces, post-war semis, and detached homes each come with different possibilities, planning considerations, and costs. To help you, we will talk about all South London extensions for 2026, what each one is best for, and how much homeowners should realistically budget.
Why Extensions Are So Popular in South London
South London has a high concentration of period properties with layouts that no longer suit modern lifestyles. Narrow kitchens, limited storage, and a lack of flexible living space are common issues. The extensions offer a solution, allowing homeowners to create open-plan kitchens, add bedrooms, or improve natural light without sacrificing location.
Single-Storey Rear Extensions
Single-storey rear extensions are common in South London. They work well for:
Larger kitchen-diners
Family living spaces
Improving flow to the garden
These extend out into the garden and can dramatically change how the ground floor works. Rooflights and large sliding or bi-fold doors are often used to maximise light.
Average cost in South London:
£60,000 - £120,000, depending on size, finishes, and glazing.
Side Return Extensions
Side return extensions are popular in Victorian and Edwardian terraces, which often have a narrow unused alleyway along one side of the property. These are best for:
Widening small kitchens
Adding utility or storage space
Creating a more balanced ground-floor layout
Although smaller than rear extensions, side returns often involve structural steelwork and drainage changes, which can affect cost. The average cost is £55,000 - £90,000.
Wrap-Around Extensions
It’s a combination of a rear extension with a side return, creating a large L-shaped addition. These are best for:
Maximum ground-floor transformation
Open-plan kitchen, dining, and seating areas
Families planning to stay long term
This type of extension creates a good visual impact but is also more complex to build. The average cost is £120,000 - £200,000+, depending on scope and specification.
Read More: Wrap-Around Extensions
Double-Storey Extensions
Double-storey extensions add space both upstairs and downstairs, making them a strong option for growing families. But a planning permission may be required. These are best for:
Adding bedrooms and bathrooms
Long-term family homes
Properties with sufficient garden space
The typical cost includes £110,000 - £180,000+
Loft Extensions as an Alternative
When garden space is limited, a loft extension can be a better option than building outwards. These are best for:
Extra bedrooms or home offices
Preserving garden space
Increasing property value efficiently
Rear dormer and mansard loft conversions are common in South London, depending on planning rules. Their typical cost is around £55,000 - £100,000.
Basement Extensions
Basement extensions are less common and considered mostly in higher-value areas. These are best for:
Adding space without altering the external footprint
Home gyms, cinemas, or additional living areas
These projects are complex and require specialist design and construction. The average cost for these extensions is £150,000 - £300,000+
Conservatories, Orangeries, and Garden Rooms
These options are best for homeowners who are looking for additional space without the cost of a full extension. Such extensions are best for:
Garden-facing living areas
Home offices or studios
Faster, lower-cost builds
The year-round usability depends heavily on insulation, glazing, and heating choices. The average cost is £20,000 - £60,000.
How Much Do South London Extensions Cost in 2026?
In 2026, most South London extension projects fall between £2,500 and £4,000 per square metre, depending on build quality and complexity. The cost changes depend on structural requirements, glazing, and internal finishes.
Many homeowners researching South London extensions are surprised to learn that kitchens, bathrooms, and professional fees are often additional costs that should be planned for from the start.
Planning Permission and Regulations
Some extensions fall under permitted development, whilst others require full planning permission. Conservation areas, listed buildings, and party wall matters are common in South London and can affect timelines.
Building Regulations always apply and cover structure, insulation, electrics, drainage, and ventilation. Failing to factor this in early can lead to delays and unexpected costs.
Choosing the Right Extension for Your Home
The right extension depends on:
Your property type
How do you want to use the space
Your budget and long-term plans
Local planning constraints
For example, side return extensions suit terraces, whilst detached homes may benefit more from double-storey builds.
Advice from Denham Crescent
Denham Crescent specialises in designing and building South London extensions that suit real homes and real lifestyles. We know local planning rules, structural challenges, and the practical realities of building in busy residential areas.
Homeowners need early feasibility and design from the planning stage to construction, and final finishes, with clear communication and realistic budgets. If you’re extending your home in 2026, a complementary professional advice is the best way to start.
Call us today to book your free site assessment.
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