Single Storey Extensions Explained: What’s Involved
In short
A single storey extension adds ground floor space to a house, usually at the rear, into a side return or as a wraparound combining both. It is the most common way London families create an open plan kitchen and living space, and many can be built under permitted development or prior approval.
A single storey extension is the classic London home improvement: knock through at the back, extend into the garden or side return, add glazing and roof lights, and create the open plan kitchen, dining and living space that so many period houses lack. Done well, it changes how a family uses the whole house.
Types of single storey extension
- Rear extension: extends straight out from the back wall of the house.
- Side return extension: fills the narrow passage beside the rear outrigger of a Victorian or Edwardian terrace, often with a glazed or sloping roof.
- Wraparound (L shaped) extension: combines side return and rear extension for the largest open plan space.
- Side extension: on semi detached and detached houses, extending to the side of the property.
Planning: what the rules currently allow
Under permitted development in England, a single storey rear extension on a house can currently extend up to 3 metres from the original rear wall (4 metres for a detached house), with a maximum height of 4 metres and eaves no higher than 3 metres within 2 metres of a boundary. Through the prior approval process, where neighbours are consulted, those depths increase to 6 metres and 8 metres. Side extensions are limited to single storey and half the width of the original house. Side return and wraparound extensions often need planning permission, and conservation areas, flats and Article 4 areas have tighter rules. Check the current position with your council before you commit to a design.
Other approvals
- Building regulations for structure, foundations, drainage, insulation, glazing and fire safety. See building regulations approval.
- Party wall notice where you build on or near the boundary or excavate close to a neighbour’s foundations.
- Build over agreement with the water company if the extension sits over a public sewer, which is common in London gardens.
The build, stage by stage
- Site set up, protection and strip out
- Foundations, drainage and the ground floor slab
- Walls, steelwork and opening up the rear of the house
- Roof, roof lights and glazing to make it weathertight
- First fix, insulation, screed and underfloor heating
- Plastering, kitchen installation, flooring and second fix
- Decoration, snagging and building control sign off
What drives the cost
Size, the amount of structural steel, glazing (large sliding or bifold doors and roof lights are significant items), ground conditions and drainage, and the specification of the kitchen and finishes. A clear schedule of works shows you where the budget goes.
How we handle single storey extensions on London’s Prestige projects
We manage your extension from start to finish: design coordination, planning or prior approval, building regulations, party wall, the build and the finished kitchen and interiors, with one project manager and clear updates every week. See the glazed side return and bifold doors on our Meadway Close wraparound extension, explore our extension service, and book a site visit to talk through your plans.
Common questions
How far can I extend without planning permission?
Currently up to 3 metres for most houses (4 metres if detached) under permitted development, or 6 and 8 metres through prior approval, subject to height and other conditions. Flats, conservation areas and Article 4 areas differ.
Do I need building regulations for a single storey extension?
Yes. Building regulations apply even when planning permission is not needed, covering structure, foundations, drainage, insulation and fire safety.
Can I live at home during a single storey extension?
Usually, with some disruption when the rear wall is opened and the kitchen is out of use. A temporary kitchen and careful sequencing keep this period as short as possible.