Designing a Flat Roof Extension with Balcony in South West London
17, May, 2025
For many homeowners in South West London, space is a luxury. As house prices continue to rise, extending your home rather than moving has become the smarter choice. Among the most stylish and functional options is a flat roof extension with a balcony, a design trend that is transforming modern homes across London.
In this blog, we explore the key considerations, benefits, and design tips for creating the perfect flat roof extension with a balcony, tailored for urban properties in South West London.
Read More: Flat Roof vs Pitched Roof: What Works in South West London?
Why Choose a Flat Roof Extension with Balcony?
A flat roof extension with balcony is not just a contemporary design statement — it’s a smart way to maximise space, light, and outdoor access in homes where garden space may be limited. The flat roof structure provides a clean, modern look and offers the ideal platform to support a functional outdoor area on top, whether that’s a roof terrace, Juliet balcony, or private seating zone.
In densely built neighbourhoods like Balham, Clapham, or Wimbledon, this type of extension offers an ideal combination of practicality and aesthetic appeal.
Planning Permission and Building Regulations
Planning a flat roof extension with balcony in South West London does require careful attention to local planning policies, especially regarding privacy, overlooking neighbours, and external appearance.
While flat roof extensions can sometimes fall under permitted development, the addition of a balcony or terrace typically requires full planning permission. South West London boroughs like Wandsworth, Lambeth, or Merton often have specific guidelines that address overlooking and visual impact, especially in conservation areas or terraced housing.
It’s always advisable to work with experienced architects or extension specialists who are familiar with your local council’s planning process to avoid costly delays or rejections.
Balcony Types to Consider
When designing a flat roof extension with balcony, you’ll have a few styles to choose from depending on your space and the intended use.
Juliet Balcony: A non-walkable balcony with railings installed outside large doors or windows. Ideal for letting in air and light without needing full structural support.
Walk-on Roof Terrace: A proper balcony or terrace built on top of the flat roof extension with decking, balustrades, and even seating areas.
Recessed Balcony: Built within the structure itself, offering more privacy and protection from the elements.
Each design comes with its own planning and structural requirements, so working with specialists is key.
Design and Material Considerations
A flat roof extension with balcony can be designed to suit both traditional and modern homes. In South West London, homeowners are often blending original architecture with clean, modern lines.
Consider using:
Frameless glass balustrades for an open and minimalist look
Decked or tiled surfaces for added style and durability
Sliding or bi-fold doors to create a seamless connection between indoors and your rooftop balcony
The materials used on your flat roof also matter. Ensure that your roofing system is suitable for foot traffic, water-resistant, and well insulated. Warm roof systems, for example, are popular in London homes due to their superior thermal performance.
Maximising Light and Views
One of the biggest advantages of a flat roof extension with balcony is the opportunity to increase natural light in your home. Large roof lights or sliding glass doors can flood your kitchen or living room with daylight while offering easy access to your private outdoor space.
If you’re lucky enough to have a skyline view over South West London, a well-positioned balcony can completely change the way you use your space — perfect for morning coffee, evening relaxation, or entertaining friends.
Cost Expectations
The cost of a flat roof extension with a balcony in South West London varies based on design complexity, materials, and permissions. As a rough guide:
Flat roof rear extensions can range from £35,000–£70,000+
Adding a usable roof balcony or terrace can increase costs by £10,000–£25,000+ depending on the size, access, and finish
Though this may seem like a significant investment, the added value to your property and lifestyle can make it worthwhile — especially in high-demand areas.
How Denham Crescent Can Help
At Denham Crescent, we specialise in bespoke flat roof extensions across South West London. Whether you're in Streatham, Tooting, or Putney, we can help you design and build a flat roof extension with a balcony that complements your home and enhances your lifestyle.
From concept to completion, we handle planning permissions, structural design, and construction, making the process seamless and stress-free. If you're considering adding space, light, and outdoor living to your home, speak with our team today to see how we can help bring your vision to life.
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