House Extension Cost in South London: Single Storey, Double Storey and Side Return
Planning an extension is often one of the biggest decisions a homeowner will make, especially in areas where space is limited and moving can be expensive. Before speaking to builders or architects, it helps to understand what affects the budget and why prices can vary so much from one property to another.
For homeowners researching house extension costs in South London, the final figure will usually depend on the type of extension, structural complexity, finish quality, access and planning requirements.
What Is the Average House Extension Cost in South London?
House extension costs in South London typically range from £2,000 to £4,000 per square metre depending on the complexity and finish of the build.
Several factors influence the final cost, including:
- Extension type
- Property access
- Structural work required
- Interior finishes
- Planning and architectural fees
- Kitchen or bathroom installations
- Steel beam requirements
- Ground conditions
South London projects can sometimes cost more than national averages due to tighter site access, parking restrictions and higher labour demand.
- Single-storey extension: Typically costs between £45,000 and £90,000+
- Double storey extension: Typically costs between £75,000 and £150,000+
- Side return extension: Typically costs between £40,000 and £85,000+
- Kitchen extension: Typically costs between £50,000 and £120,000+
These figures are intended as general guidance only and should always be confirmed through a detailed site assessment and quotation.
Single-Storey Extension Cost in South London
A single-storey extension is often the most popular option for homeowners wanting to expand kitchens, dining areas or open plan-storey-plan living spaces.
In South London, the average single storey-plan-storey extension cost is usually between £45,000 and £90,000 depending on size and specification.
What affects the cost?
The main pricing factors include:
- Rear extension size
- Bi fold-storey-fold or sliding doors
- Rooflight installation
- Structural steelwork
- Underfloor heating
- Kitchen fitting
- Bespoke glazing
- Interior finish quality
A straightforward rear extension with standard finishes will naturally cost less than a fully customised architectural build with premium materials.
Many homeowners choose single-storey-fold extensions because they can dramatically improve day-to-day living without the disruption of moving house.
Double Storey Extension Cost
Double storey extensions generally offer better value per square metre because the roof and foundations are shared across two levels.
In South London, double-storey extension costs commonly range from £75,000 to £150,000 or more.
This type of extension is ideal for:
- Adding extra bedrooms
- Creating additional bathrooms
- Enlarging kitchens and living spaces simultaneously
- Increasing family accommodation
Why are double-storey extensions more complex?
Although more cost-effective per square metre, they involve additional structural and planning considerations, including:
- Staircase integration
- Load-bearing calculations
- More extensive steelwork
- Fire safety compliance
- Potential neighbour impact
Planning approval is often required, particularly in conservation areas or where overlooking may become an issue.
Working with experienced extension builders is important to ensure the project runs smoothly and complies with UK building regulations.
Side Return Extension Cost in London
Side return extensions are especially common in Victorian and Edwardian terraced homes throughout South London.
A side return extension typically costs between £40,000 and £85,000 depending on layout and specification.
These extensions utilise the unused alleyway space at the side of a property to widen the ground floor, often transforming narrow kitchens into large open-plan living areas.
Why are side return extensions popular?
They can:
- Improve natural light
- Create better kitchen layouts
- Increase property appeal
- Maximise unused external space
- Enhance open-plan living
However, side return projects can involve structural complexity because existing external walls are often removed and replaced with steel supports.
Party wall agreements may also be required where neighbouring properties are affected.
What Additional Costs Should You Budget For?
Many homeowners focus only on construction costs, but a successful extension project also requires professional services and finishing costs.
Additional expenses may include:
- Architectural drawings
- Structural engineer fees
- Planning application fees
- Building control fees
- Party wall surveyors
- Temporary accommodation if needed
- Landscaping and decorating
- VAT
It is sensible to keep a contingency budget of around 10 to 15 per cent for unforeseen costs.
Older South London properties can sometimes reveal hidden structural or drainage issues once work begins.
Is a House Extension Worth the Investment?
For many homeowners, extending is more cost-effective than moving, particularly in high-value South London areas.
A well-designed extension can:
- Improve quality of life
- Add functional space
- Increase property value
- Avoid moving costs and stamp duty
- Future-proof a family home
The key is ensuring the design, layout and build quality align with both your lifestyle and your long-term property goals.
Choosing an experienced local builder can also help avoid delays, budget overruns and compliance issues.
Choosing Experienced Extension Builders in South London
Choosing the right contractor is an important part of any extension project. Homeowners should look for experienced builders with strong local knowledge, transparent quotations and a proven track record of quality work. If you are planning a house extension in South London, contact Doran Bros Construction to discuss your project with our team.
At Doran Bros Construction, we specialise in high-quality house extensions across South London, helping homeowners create practical and beautifully finished living spaces tailored to modern family needs.
Frequently Asked Questions
How much does a kitchen extension cost in South London?
A kitchen extension in South London usually costs between £50,000 and £120,000 depending on size, layout and specification.
Do I need planning permission for a house extension?
Some extensions fall under Permitted Development rights, but larger or more complex projects may require planning permission.
How long does a house extension take?
Most house extensions take between 3 and 6 months depending on complexity and structural requirements.
Is a double-storey extension better value?
In many cases, yes. Double storey extensions often provide more space for a lower cost per square metre.
What type of extension adds the most value?
Open-plan kitchen extensions and additional bedroom space typically provide the strongest return in family homes.