A Single Storey Rear Extension is one of the easiest ways to add space to your home. It works well for kitchens, dining rooms, and family areas. Most homeowners choose it because it costs less than moving.
This guide covers cost, planning rules, design ideas, and timelines. You will also learn how to avoid the mistakes that cause delays and budget overruns.
What Is a Single Storey Rear Extension?
This type of build is a new ground floor room built onto the back of your house. It usually replaces a small kitchen or an unused garden area with open, usable space. Most homeowners use this type of build to create a bigger kitchen-diner. Others use it for a playroom, home office, or extra living room. Unlike a loft conversion or a two storey build, this project stays on one level. That keeps costs down and avoids many of the planning headaches tied to upper floor additions.Why Homeowners Choose This Extension Type
- Adds usable floor space without moving house
- Often falls under permitted development, saving time
- Brings in more natural light through glazing and rooflights
- Increases property value in most UK markets
- Suits terraced, semi-detached, and detached homes
Planning Permission and Permitted Development Rights Explained
One of the biggest questions homeowners ask is whether they need planning permission. In most cases, the answer is no. Many single storey rear extensions fall under permitted development rights. These are national rules that let you build without a full planning application, as long as you stay within set limits. Extra Reading: House Extension TypesStandard Permitted Development Limits
- Terraced and semi-detached houses: up to 3 metres from the original rear wall
- Detached houses: up to 4 metres from the original rear wall
- Maximum height of 4 metres overall
- Eaves height of no more than 3 metres if within 2 metres of a boundary
- The extension must not cover more than half the garden
- Materials should match the existing house in appearance
The Larger Home Extension Scheme
If you want to build bigger, the Larger Home Extension Scheme lets you extend further. Terraced and semi-detached homes can reach 6 metres. Detached homes can reach 8 metres. This route needs a prior approval application. Your council checks your plans and gives neighbours 21 days to raise concerns. It is not full planning permission, but it does add a few weeks to your timeline.When You Will Need Full Planning Permission
- Your home sits in a conservation area or has an Article 4 direction
- The property is listed
- You want to exceed the permitted development size limits
- The design uses very different materials from the existing house
- Previous owners have already used up the permitted development allowance
Building Regulations You Cannot Skip
Even if you avoid planning permission, you still need to follow building regulations. These rules cover safety, insulation, drainage, and structural strength. Building control will check your extension at key stages, including foundations, drainage, and final completion. Skipping this step can cause serious problems if you sell your home later.Key Areas Building Control Will Check
- Foundation depth and ground conditions
- Insulation levels in walls, floor, and roof
- Fire safety, including escape routes
- Drainage and waste connections
- Structural support, including steel beams where needed
Why You Need a Structural Engineer
Almost every rear extension needs a structural engineer. They calculate loads, design steel beams, and confirm your foundations are strong enough. If you are removing a wall between the house and the new extension, a beam is almost always required. Your structural engineer works out the size and position, then hands the plans to building control. Skipping this step is one of the most common reasons projects fail inspection. It is not an area to cut corners. Extra Reading: Do I Need an Architect for an ExtensionRear Extension Design and Layout Ideas
Good rear extension design starts with how you actually live day to day. Think about how your family moves through the kitchen, dining space, and garden.Popular Layout Choices
Open-plan kitchen extension layouts remain the most requested design in 2026. They combine cooking, eating, and living space into one bright room. Other popular rear extension ideas single storey projects include:- A glazed box extension with full-width bi-fold or sliding doors
- A vaulted or lantern roof for extra ceiling height and light
- A flat roof with rooflights above the kitchen island
- A rear extension that flows into a side return for an L-shaped plan
- A separate snug or reading nook off the main open space
Getting the Extension Layout Right
Your extension layout should balance cooking, dining, and lounging zones without feeling cramped. A good rule is to keep circulation paths clear, especially near doors to the garden. Many homeowners researching single storey rear extension ideas want a kitchen island as the centrepiece. This works well if the room is at least four metres wide, giving enough space to walk around it comfortably.Maximising Natural Light
- Use full-width glazing across the rear wall
- Add a roof lantern above the kitchen or dining area
- Include rooflights along a flat roof section
- Choose slim sightline windows and doors to reduce visual clutter
- Keep internal walls to a minimum for an open, bright feel
How Much Does a Single Storey Rear Extension Cost?
Cost is usually the first question homeowners ask, and for good reason. Prices vary by size, location, and finish.2026 UK Cost Guide
- National average: roughly £1,800 to £3,000 per square metre
- London and the South East: roughly £2,800 to £4,500 per square metre
- A 20 square metre extension: around £40,000 to £70,000 all in
- A 30 square metre extension: around £60,000 to £110,000 all in
What Affects the Final Price
- Size and shape of the extension
- Roof type, flat roofs cost less than pitched or lantern designs
- Glazing choice, bi-fold and sliding doors add cost
- Ground conditions and foundation depth
- Site access, tight urban plots often cost more to build
- Specification level of the kitchen and finishes
How Long Does It Take?
A typical project of this size takes 10 to 16 weeks to build. The full process, from design through completion, usually runs 4 to 8 months once you include planning, structural design, and building control approval. Weather, ground conditions, and material delays can extend this timeline. Building during autumn or winter sometimes adds extra weeks for groundworks.Common Mistakes to Avoid
- Skipping a structural survey before finalising the design
- Choosing a builder based only on the lowest quote
- Ignoring drainage and manhole positions during planning
- Underestimating disruption while living in the house during the build
- Forgetting party wall agreements with semi-detached or terraced neighbours