If you’re considering extending your home, one of the first questions you’re likely to ask is: how much does a house extension cost in Cambridge?
A house extension can be an excellent way to create more living space without the disruption and expense of moving. Whether you’re looking for a larger kitchen, an additional bedroom, a home office or a completely new family living space, a well-designed extension can transform the way you use your home.
However, there is no single price for a house extension. The final cost depends on the size and type of extension, the materials and finishes you choose, the complexity of the work, the condition of the existing property and the requirements of your site.
As a general 2026 budgeting guide, UK construction cost sources place a standard house extension at around £1,800–£3,000 per m² before VAT, with Cambridge and the wider South East potentially sitting towards the higher end depending on specification and site conditions. These figures should only be used for initial budgeting rather than as a quotation.
What Does a House Extension Cost in Cambridge?
The simplest way to start estimating the cost of an extension is to consider its floor area.
For example, using an indicative range of £1,800–£3,000 per m²:
- A 15m² extension could start from around £27,000–£45,000
- A 20m² extension could be around £36,000–£60,000
- A 30m² extension could be around £54,000–£90,000
- A 40m² extension could be around £72,000–£120,000
These are illustrative build-cost calculations, not quotes. The actual cost of a Cambridge house extension can vary significantly depending on the specification and property.
A recent Cambridge-specific cost model, for example, estimates a 30m² single-storey extension at a considerably higher total once the full project specification and local costs are accounted for. This highlights why homeowners should be cautious about relying on a simple price-per-square-metre calculation.
What Affects the Cost of a House Extension?
Several factors can have a major impact on your final extension budget.
1. The Size of the Extension
Naturally, the larger your extension, the more materials, labour and time will be required.
However, cost does not always increase in a perfectly linear way. A small extension may still require foundations, drainage, structural work, electrical installation, plumbing and other fixed costs.
2. Single-Storey or Double-Storey?
A double-storey extension can provide considerably more additional floor space.
Although it costs more overall, the cost per square metre can sometimes be lower than building two completely separate single-storey structures because the foundations and some structural elements can serve both floors.
The design and structural requirements will ultimately determine whether this is the right approach for your property.
3. The Type of Extension
The design of your extension will also affect the price.
Common options include:
- Rear extensions
- Side extensions
- Side-return extensions
- Kitchen extensions
- Single-storey extensions
- Double-storey extensions
- Wrap-around extensions
- Bathroom extensions
At Stefan’s Building, we provide bespoke house extensions throughout Cambridge and Cambridgeshire, including single and double-storey extensions, kitchen extensions, side and rear extensions, bathroom extensions and wrap-around extensions.
4. Your Choice of Materials
Your choice of bricks, windows, doors, roofing, flooring and internal finishes can all influence the final price.
For example, a basic specification will naturally have a different budget from an extension incorporating:
- Large areas of glazing
- Bi-fold or sliding doors
- Roof lanterns
- Premium flooring
- Bespoke joinery
- Underfloor heating
- A new kitchen
- High-end bathroom fittings
It’s therefore important to decide on your desired specification as early as possible.
5. Ground Conditions and Foundations
Before construction can begin, your builder needs to establish what foundations are appropriate for the extension.
Ground conditions, nearby trees, drainage, existing structures and the design of the extension can all affect the foundation requirements.
Unexpected ground conditions can also increase costs, which is one reason why having appropriate surveys and professional design work completed before construction is so important.
6. Structural Alterations
Many extensions involve making changes to the existing house.
For example, you might want to remove an external wall to create a large opening between your existing kitchen and the new extension.
This can require structural steelwork and careful temporary support during construction.
7. Plumbing and Electrical Work
If you’re building a kitchen, utility room, bathroom or additional bedroom, you’ll probably need new plumbing, heating and electrical work.
These costs need to be considered as part of the overall project rather than treated as an afterthought.
Do You Need Planning Permission for a House Extension?
Not every house extension requires a full planning application.
Certain extensions may fall within permitted development rights, provided that they meet all the relevant limitations and conditions. The rules cover factors such as the size, height, position and design of the proposed extension.
However, permitted development rights can be affected by factors including:
- The location of your property
- Conservation area status
- Listed-building status
- Article 4 Directions
- Previous planning permissions
- The design and dimensions of the extension
Greater Cambridge Shared Planning provides guidance for local homeowners, and Cambridge residents can also use its current online “Do I Need Planning Permission?” service for an initial indication of whether permission may be required.
Remember that planning permission and Building Regulations are separate matters. Even where planning permission isn’t required, Building Regulations may still apply.
How Can You Keep Your Extension Within Budget?
The best way to control costs is to plan as much as possible before construction begins.
Start by establishing:
- What space you actually need
- The size of extension required
- Your preferred layout
- Your desired specification
- Whether planning permission is required
- Whether structural calculations are needed
- Your overall budget
- Your contingency allowance
Avoid making major changes once construction has started wherever possible. Design changes, upgraded finishes and additional work can quickly increase the final cost.
Why Choose an Experienced Cambridge Builder?
Choosing the right builder in Cambridge can make a significant difference to your experience.
A professional builder should be able to help coordinate the different elements of your project, from initial planning and structural work through to construction and finishing.
Stefan’s Building provides fully managed house extensions across Cambridge and Cambridgeshire. The company has more than four decades of experience and is a member of the Federation of Master Builders. Its extension service covers planning support, groundworks, structural alterations, roofing, windows and doors, plumbing, electrical work, plastering, flooring and final sign-off.
Get a Quote for Your Cambridge House Extension
Every property is different, so the best way to establish the cost of your project is to have your proposed extension assessed and obtain a detailed quotation based on its actual requirements.
If you’re considering a house extension in Cambridge or Cambridgeshire, Stefan’s Building can help you plan and manage your project from the initial design through to completion.
Get in touch with Stefan’s Building to discuss your requirements and start planning your new space.