How much does a rear extension cost in Sussex?

‍

If you are asking how much a rear extension costs in Sussex, the honest answer is: it depends on the size, specification, structure, and level of design involved. But in 2026, most homeowners are not just looking for a rough number. They want a realistic budget, clear expectations, and confidence that the final cost will not spiral halfway through the build.

A rear extension is one of the most popular ways to create more living space without moving house. It can open up the back of the property, improve flow, bring in more natural light, and create the kind of kitchen, dining, and family space that modern homeowners actually want to use.

In Sussex, costs vary based on location, site conditions, access, finishes, and whether you are extending a modest terraced home or a larger detached property. As a broad guide, many rear extensions fall somewhere between £2,200 and £3,500+ per square metre, with premium projects exceeding that depending on glazing, steelwork, bespoke joinery, and structural complexity.

Quick answer: typical rear extension cost ranges in Sussex

‍

Here is a practical starting point for 2026:

• Small single-storey rear extension: from £35,000 to £60,000+

• Medium single-storey rear extension: from £60,000 to £95,000+

• Large single-storey rear extension: from £95,000 to £150,000+

• High-spec or structurally complex rear extension: £150,000+

These figures are not one-size-fits-all. They are broad budgeting ranges, not fixed quotes. The final cost depends on what is included.

What affects the cost of a rear extension?

‍

1. Size of the extension

The bigger the extension, the higher the total cost. But cost per square metre does not always reduce dramatically, because kitchens, glazing, drainage, and structural changes can keep costs high even on smaller projects.

2. Structural complexity

If the design requires significant steelwork, large openings, complex foundations, or major changes to the existing house, costs will rise.

3. Ground conditions

Poor soil, drainage issues, trees, slopes, or nearby structures can all affect foundation design and build cost.

4. Specification and finishes

There is a big difference between a straightforward extension shell and a finished family space with rooflights, sliding doors, underfloor heating, bespoke cabinetry, and premium flooring.

5. Kitchen and interior fit-out

A rear extension often includes a new kitchen, utility area, flooring, decorating, and lighting. These can make up a substantial share of the overall budget.

6. Design and professional input

Architectural design, structural engineering, planning input, building regulations, and project coordination all affect the budget, but they also reduce risk.

Single-storey rear extension cost in Sussex

‍

For many homeowners, a single-storey rear extension cost in Sussex will depend on whether the goal is a simple extra room or a full open-plan transformation.

A modest rear extension with standard finishes may sit at the lower end of the range. A more ambitious design with large-span glazing, kitchen relocation, and premium detailing will sit much higher.

This is why online averages can be misleading. Two extensions with the same footprint can have very different final costs.

What is usually included in the cost?

‍

A realistic rear extension budget may include:

• Design drawings

• Structural engineering

• Planning support where needed

• Building regulations drawings and compliance

• Groundworks and foundations

• Drainage works

• Structural shell and roofing

• Insulation and plastering

• Windows and doors

• Electrics and plumbing

• Heating

• Flooring and decorating

• Kitchen or interior fit-out

If a quote looks unusually cheap, it is often because some of these items are missing.

Planning permission and permitted development

‍

Some rear extensions can be built under permitted development, while others require planning permission. The answer depends on the property, the size of the proposal, and any site-specific restrictions.

Even where planning permission is not required, building regulations approval still will be.

For homeowners in Sussex, local context matters. Conservation areas, planning history, and design sensitivity can all affect what is possible.

Hidden costs homeowners often miss

‍

When people search how much does a rear extension cost, they often focus only on the build. In reality, there can be additional costs such as:

• Party wall matters

• Upgrading drainage

• Moving manholes

• Temporary kitchen arrangements

• Structural surprises in the existing house

• Decorating adjoining rooms

• Landscaping after the build

• Furniture and final styling
  ‍

This is where early planning pays off.

How to budget properly for a rear extension

‍

A sensible budgeting approach is:

1. Set a realistic all-in budget, not just a build budget

2. Decide what matters most: size, finish, glazing, kitchen, or flexibility

3. Allow contingency for unknowns

4. Get proper design input before pricing

5. Compare like-for-like quotes, not headline numbers
   ‍

The goal is not just to build more space. It is to create the right space at the right level of investment.

Is a rear extension worth it?

‍

For many homeowners, yes. A rear extension can improve layout, increase usable space, and make the home work far better for modern life. It can be especially valuable for growing families, homeowners who love entertaining, or people who want a brighter kitchen-living-dining area.

In many cases, the value is not just financial. It is about staying in the area you love while making the house fit your life better.

Rear extension costs in Sussex: why local experience matters

‍

Rear extension costs in Sussex are shaped by more than square metre rates. Access constraints, local planning expectations, site conditions, and the age of the property all influence the final figure.

That is why local design and build experience matters. A joined-up team can spot risks early, coordinate design and construction properly, and give homeowners a clearer picture of costs before work starts.

Why STAAC is well placed to help

‍

STAAC brings architects, structural engineers, and builders together under one roof. That means homeowners do not need to juggle separate consultants and contractors while hoping everyone stays aligned.

With fixed pricing, no hidden fees, and a 10-year warranty on every build, STAAC offers a more transparent route from concept to completion. The integrated model can help clients save time, reduce friction, and move forward with more confidence.

FAQ

‍

How much does a rear extension cost in Sussex in 2026?

Many rear extensions in Sussex fall between £35,000 and £150,000+, depending on size, complexity, and specification.

What is the average single-storey rear extension cost?

A single-storey rear extension often starts from around £35,000 to £60,000+ for smaller projects, with medium and high-spec projects costing significantly more.

What adds the most cost to a rear extension?

Common cost drivers include structural changes, glazing, kitchens, ground conditions, drainage works, and premium finishes.

Do I need planning permission for a rear extension?

Some rear extensions fall under permitted development, while others need planning permission. It depends on the property and proposal.

How can I keep rear extension costs under control?

Start with a realistic budget, get proper design input early, compare detailed quotes, and work with a team that can manage design and construction together.

Thinking about a rear extension in Sussex? Speak to STAAC for clear advice, realistic budgeting, and a joined-up design and build process that takes your project from first ideas to finished space.

‍

‍