Cost of a Ground Floor Extension: What You Will Actually Pay in the UK
28, Apr, 2026
If you’re planning to extend your home, you’ve probably already seen a wide range of prices. Some quotes feel reasonable. Others feel far too high. The problem is not just the numbers, it’s understanding what those numbers include.
The real cost of a ground floor extension is not a single figure. It depends on how your home is built, what you want to achieve, and how complex the work becomes once construction starts.
How Much Does a Ground Floor Extension Cost in the UK?
Most ground floor extensions in the UK fall within a predictable range, but the final price depends on detail. As a guide:
£2,500 to £4,000 per m² is the typical cost range
£60,000 to £80,000 for a modest extension
£80,000 to £120,000+ for larger or more complex builds
These figures apply to most London and South London projects, where labour and materials are generally higher than in other regions.
The key point is this. Two extensions of the same size can still have very different costs depending on structure, finishes, and layout changes.
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Ground Floor Extension Cost by Type
The type of extension you choose has a direct impact on cost.
A rear extension is usually the most straightforward. It extends directly into the garden and often involves fewer structural complications.
A side return extension, common in terraced homes, can be more complex. Although it may look smaller, it often requires careful structural work and drainage adjustments.
A wrap-around extension combines both. It creates the most space but also involves the highest cost due to increased structural work and layout changes.
This is why the design stage matters. Choosing the right type of extension can control costs before the build even begins.
Cost Per m²: What Does It Actually Include?
The cost per square metre is often quoted, but it doesn’t always explain what you are paying for. At the lower end, around £2,500 per m², you are looking at a basic structure with standard finishes.
As you move towards £3,500 to £4,000 per m², this usually includes:
Larger openings and structural steel
Higher quality glazing, such as sliding or bi-fold doors
Upgraded finishes and fittings
This is why focusing only on the m² rate can be misleading. The details behind the design have a bigger impact on the final cost.
Where Does the Money Go?
A ground floor extension is made up of several stages, and each one contributes to the overall cost. A typical breakdown includes:
Structural work and foundations
Labour across multiple trades
Materials such as brickwork, roofing, and insulation
Glazing, flooring, and internal finishes
Structural work and labour usually take up the largest share. Finishes can vary widely depending on your choices.
What Increases the Cost of a Ground Floor Extension?
Some factors increase the cost more than others. Understanding these early helps you plan properly. The main cost drivers are:
Structural changes, such as removing load-bearing walls
Large glass doors or rooflights
Difficult access to the site
Complex layouts that require more coordination
Location, with London projects often costing more
Even small design changes can affect cost significantly. For example, widening an opening for glazing can require additional steelwork.
Hidden Costs You Should Expect
Many homeowners plan for the build itself but overlook additional costs that come with the project. These can include:
Planning application fees if required
Structural engineer calculations
Building control inspections
Party wall agreements with neighbours
These costs are not always included in initial quotes, but they are part of the overall budget.
Planning Permission and Regulation Costs
Not every ground floor extension requires full planning permission. Some fall under Permitted Development, depending on size and location.
However, even when planning permission is not needed, Building Regulations always apply. These ensure the extension is safe, insulated, and structurally sound.
Planning and approval costs are usually a small part of the total budget, but they play a key role in avoiding delays and complications later.
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How Long Does a Ground Floor Extension Take?
Time also affects cost. The longer a project runs, the more it can cost in labour and coordination.
Most ground floor extensions take:
8 to 12 weeks for construction
Additional time for design, approvals, and preparation
A well-planned project tends to stay on budget because delays are reduced.
Is a Ground Floor Extension Worth the Cost?
For many homeowners, the decision comes down to value. Moving house is expensive, and house extensions often provide a better long-term solution.
A well-designed extension can:
Improve how your home functions
Increase property value
Create an open, usable living space
The key is making sure the design solves the right problem rather than just adding space.
Common Cost Mistakes to Avoid
Many budget issues come from early decisions rather than construction problems.
A common mistake is choosing a contractor based only on price. Lower quotes can sometimes exclude important elements, which then appear later as extra costs.
Another issue is not finalising the design before building begins. Changes during construction almost always increase cost.
Clear planning at the start leads to better control over the budget.
Plan Within Budget With Denham Crescent
At Denham Crescent, we focus on making costs clear from the beginning. We assess your property, understand how you want to use the space, and explain what is realistically possible within your budget.
Rather than working from assumptions, we provide structured guidance on layout, cost, and construction before any work begins. This approach helps reduce surprises and ensures the final result matches what you expected.
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