House extension architects

An extension either transforms how a house works or wastes a lot of money moving a wall. The difference is in the plan: where the light lands, where the kitchen sits, and how the new space meets the garden.

We design extensions that pass planning and work day to day, then produce the technical set your builder prices from.

Extension types

Single-storey rear extension

The most common project we do. Typically opens up a kitchen and dining space across the back of the house with sliding or bi-fold doors and rooflights over the deep plan.

Side return extension

Fills the narrow alley beside the rear outrigger of a Victorian terrace. It rarely adds much floor area on paper, but it changes the whole ground floor from a series of small rooms into one wide space.

Wrap-around extension

Rear and side return combined. The biggest ground-floor gain available on a typical terrace, and usually the point at which full planning permission is needed rather than permitted development.

Two-storey and first-floor extensions

Adds a bedroom or bathroom above. Nearly always needs planning permission, and daylight, overlooking and the impact on neighbours have to be handled carefully in the design.

Garage conversions and outbuildings

Garden studios, home offices and garage conversions. Often permitted development, subject to height, position and the proportion of garden covered.

Basements

Excavation under the footprint or garden. Most London boroughs now have specific basement policies covering depth, extent and construction method, and a structural method statement is normally required with the application.

Permitted development limits for rear extensions

For houses, single-storey rear extensions are commonly allowed without planning permission within these limits:

• Up to 3m deep for a terraced or semi-detached house, or 4m for a detached house.
• Maximum height of 4m, or 3m if within 2m of a boundary (eaves limit).
• No more than half the land around the original house covered by buildings.
• Materials similar in appearance to the existing house.

Deeper extensions — up to 6m on a terraced or semi-detached house, or 8m on a detached house — can be possible through the prior approval route, where the council notifies your neighbours and considers their objections about impact. It is a lighter process than full planning but it is still an application, and it has a deadline of its own.

What the council actually looks at

• Daylight and sunlight to neighbouring windows, often assessed using the 45-degree and 25-degree rules in the borough's design guidance.
• Overlooking from new first-floor windows and terraces.
• Character — whether the extension is subordinate to the original house, and whether the materials and window proportions sit properly with it.
• Garden loss and biodiversity, increasingly with drainage and permeable surfacing conditions attached.

Beyond planning

Planning permission is not permission to build. You will also need building regulations approval, and usually a party wall agreement if you are building on or near a shared boundary. We produce the construction drawings, structural coordination and specification for both, so there is no gap between the approval and the build.

Typical programme