A single storey extension is the most popular way to add space to a home. Whether you’re creating a larger kitchen, an open-plan family room, or a garden room, a well-designed single storey extension can transform how you live.
Types of Single Storey Extension
Rear Extension
The most common type, extending into the back garden. Rear extensions are ideal for expanding kitchens and creating open-plan living spaces with good connection to the garden.
Typical size: 15-40 square metres
Ideal for: Kitchen-diners, family rooms, garden rooms
Planning: Often permitted development up to 3-8 metres
Side Extension
Built into the side return or side passage, typically on Victorian and Edwardian terraced houses. Side extensions are narrower but can significantly improve a cramped kitchen layout.
Typical size: 5-15 square metres
Ideal for: Kitchen extensions, utility rooms
Planning: Must not exceed half the width of the original house
Wrap-Around Extension
Combines a rear and side extension into an L-shaped addition, maximising the available space. This option works particularly well on corner plots and end-of-terrace houses.
Typical size: 25-50 square metres
Ideal for: Large kitchen-diners, open-plan living
Planning: Usually requires planning permission
Orangery or Garden Room
A glazed extension with a lantern roof, providing a bright transitional space between house and garden. Orangeries have more solid walls than conservatories, making them usable year-round.
Typical size: 15-30 square metres
Ideal for: Dining rooms, sitting rooms, home offices
Planning: May be permitted development depending on glazing ratio
Design Considerations
Light and Space
A successful single storey extension maximises natural light. Key design elements include:
- Large sliding or bifold doors connecting to the garden
- Roof lights or a lantern roof to bring light deep into the plan
- Side windows where possible
- Light-coloured finishes to reflect natural light
Consider how the extension affects light to existing rooms. A long, narrow extension might create a dark corridor effect if not carefully designed.
Open Plan vs Broken Plan
While fully open-plan layouts are popular, ‘broken plan’ designs are gaining favour. These use subtle dividers like changes in floor level, sliding screens, or furniture to define zones while maintaining visual connection.
Benefits of broken plan:
- Reduces noise transfer between zones
- Contains cooking smells to the kitchen area
- Creates cosier, more intimate spaces
- Allows different activities to happen simultaneously
Roof Design
The roof is a key design element with implications for both aesthetics and planning:
- Flat roof: Clean, modern appearance; easier to construct; can have green roof or terrace
- Pitched roof: Traditional appearance; may be required in conservation areas
- Lantern roof: Statement feature; creates dramatic central light source
- Part-glazed roof: Maximises light; popular for kitchen extensions
Indoor-Outdoor Connection
Modern extensions blur the boundary between inside and outside:
- Large glazed openings: Bifold, sliding, or pivot doors
- Continuous flooring: Same material inside and out
- Level thresholds: Flush transitions for seamless flow
- External rooms: Covered terraces extending the living space
Permitted Development Rules
Single storey rear extensions often qualify as permitted development, meaning no planning permission is required. The key limits are:
Depth from Rear Wall
- Attached houses: 3 metres (or 6 metres under Prior Approval)
- Detached houses: 4 metres (or 8 metres under Prior Approval)
Height Restrictions
- Maximum height: 4 metres
- Eaves height within 2m of boundary: 3 metres
Other Requirements
- No more than half the garden area covered by extensions
- Materials similar in appearance to the existing house
- No extension forward of the principal elevation facing a highway
If your extension exceeds these limits, you’ll need to apply for planning permission. Properties in conservation areas or with Article 4 directions may have more restricted permitted development rights.
Single Storey Extension Costs
Costs depend on size, specification, and location. Here’s a guide for London and Surrey:
| Extension Size | Cost Range (London/Surrey) |
|---|---|
| Small (10-15 sqm) | £35,000 – £55,000 |
| Medium (15-25 sqm) | £50,000 – £85,000 |
| Large (25-40 sqm) | £80,000 – £130,000 |
| Wrap-around (30-50 sqm) | £100,000 – £180,000 |
These costs include construction, standard finishes, and bifold doors. Kitchen fit-out, high-end finishes, and professional fees are additional.
Common Mistakes to Avoid
Going Too Small
An extension that’s too small often creates an awkward space that doesn’t function well. The cost per square metre decreases as size increases, so adding an extra metre or two is often worth the investment.
Ignoring the Existing House
The extension should integrate with your existing home, not feel like a separate addition. Consider how rooms flow together and how the extension affects circulation throughout the house.
Underestimating Disruption
A rear extension typically takes 3-5 months to complete. During construction, you’ll likely lose access to your garden and may have limited kitchen facilities. Plan for the disruption.
Skimping on Glazing
High-quality glazing is expensive but transformative. Aluminium frames, large glass panels, and minimal sightlines create a contemporary look that cheaper systems can’t match.
The Design Process
At Composition Design Architects, we follow a structured process:
- Initial consultation: Understand your requirements and assess your property
- Concept design: Develop options for layout, form, and materials
- Developed design: Refine the chosen option and prepare planning drawings
- Technical design: Produce detailed construction information
- Construction: Administer the building contract and inspect the works
We work with you at every stage to ensure the final result meets your needs and exceeds your expectations. You can also learn more about our team and view our portfolio.
Ready to Start?
If you’re considering a single storey extension in London or Surrey, contact us for an initial consultation. We’ll visit your property, discuss your requirements, and explain what’s achievable within your budget and planning constraints.
We work across London and Surrey, including Wimbledon, Wandsworth, Putney, Kingston, Surbiton, Guildford, Cobham, and Esher.
Get in touch to arrange your consultation.