How to Get the Most From a Small Extension
Not all extensions need to be large to be transformative. A carefully designed extension of 10–20m² — the kind that typically falls within Permitted Development on a London terraced house — can make an enormous difference to how a home functions and feels. Here's how to maximise impact from a relatively modest addition.
Understand What the Extension Is For
Before designing a small extension, be clear about its purpose. Are you extending to create a larger kitchen? To add a dining area adjacent to an existing kitchen? To improve the garden connection? To create an extra ground-floor room? The purpose determines the optimal configuration, the position of doors and glazing, and the relationship between the new space and the existing house.
A small extension that tries to do too many things simultaneously — kitchen plus dining plus office plus garden connection — often does none of them particularly well. Focus on one or two functions and design the space to serve them excellently.
Maximise Light
In a small extension, natural light is particularly important. A generously glazed rear wall (bifold or sliding doors) plus one or two rooflights makes a 12m² extension feel considerably larger than its floor area suggests. The quality of light in a small, well-glazed space can surpass that in a larger, poorly-lit one.
Consider glazing on both the rear wall and in the roof. A flush threshold between interior and exterior (or a single step down to a terrace) extends the visual and physical space further.
Connection to the Existing House
A small extension that connects to the existing house through a narrow door or a single opening feels disconnected from the rest of the home. Opening up the full width of the rear wall of the existing house — a structural opening with a beam across the full width — creates a seamless connection and makes the extension feel like an integral part of the home rather than an addition.
This structural opening typically adds £5,000–£15,000 to the cost of the project but transforms the spatial quality of the result. It's almost always worth it.
Simplicity of Design
In a small extension, simplicity of design is a virtue. A well-detailed, simple flat roof with quality rooflights and clean internal finishes will always outperform a more complex roof form with multiple junctions and materials in a small footprint. Complexity adds cost, adds risk of water ingress, and rarely improves the spatial quality of a small extension.
Budget Reality
A well-specified 12–15m² rear extension in London typically costs £35,000–£65,000 including design and professional fees. The per-square-metre cost of small extensions is higher than larger ones — fixed costs (scaffolding, structural works, M&E connections) are shared over fewer square metres. This is worth understanding when comparing the cost of a small extension to a larger one.