Guide to London House Extensions: Costs, Process & Timelines

Extending your home is one of the most effective ways to gain extra space without the expense and disruption of moving. Whether you’re looking to create an open-plan kitchen, add a new bedroom, or build a larger living area, a well-planned extension can significantly improve both the functionality and value of your property. However, the process can feel complex, especially in London where planning regulations, construction constraints and varying costs all play a major role. This guide breaks down the essentials to help you understand what to expect from a house extension project in the capital.

1. Understanding the Costs

Extension costs in London depend heavily on the scale of the project, the structure of your property and the level of finish you choose. Smaller single-storey extensions can be relatively straightforward, while larger or multi-storey builds often require more structural work and professional input. London prices tend to be higher than the national average due to material costs, labour demand and limited site access, but a well-designed extension can also deliver strong long-term value. Speaking with an experienced contractor early on will help you establish a realistic budget and avoid unexpected expenses later.

2. The Planning and Design Process

Before any construction begins, you’ll need a clear design plan. Many London properties fall within conservation areas or have specific planning restrictions, so understanding what is allowed on your street is important. Some projects may fall under permitted development, making the process quicker, while others require a full planning application. Working with a design and build contractor can simplify this stage, as they can take care of drawings, applications and structural calculations while ensuring the design is practical and cost-effective.

3. Construction Timelines

Timelines vary based on the type and scale of extension. A small rear extension might take several weeks, while larger double-storey builds can take several months from groundwork to completion. Access restrictions, weather and structural challenges can also influence timescales, particularly in densely built London neighbourhoods. A good contractor will provide a clear schedule and regular updates so you know exactly what stage the build is at and what to expect next.

4. Common Types of Extensions in London

Rear extensions and side-return extensions are extremely popular in Victorian and Edwardian homes, allowing homeowners to transform narrow layouts into bright, open-plan living spaces. Loft conversions often complement ground-floor extensions by adding extra bedrooms or bathrooms. Double-storey extensions, although more complex, can dramatically increase the size and value of a property. Each type requires different structural considerations, so choosing a builder with experience in London homes is crucial for a smooth process.

5. Working With the Right Contractor

A successful extension requires coordination between design, construction and project management. Choosing a contractor who understands London’s unique building challenges — from tight access points to party wall agreements — will make the experience more efficient and less stressful. At Building Blueprints, we handle the full process from concept to completion, ensuring your extension is delivered with quality workmanship, transparent communication and a focus on long-term durability.

Extending your home is a significant investment, but with careful planning and the right team in place, it can transform the way you live. If you're considering an extension and want expert guidance on costs, design or feasibility, Building Blueprints is here to help every step of the way.