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How Much Does a House Extension Cost in Derby?
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How Much Does a House Extension Cost in Derby?
The cost of building an extension in Derby depends on the size of the project, the type of extension, the amount of structural work involved and the level of finish.
Current 2026 local Checkatrade data puts the average extension project in Derby at around £27,218, with typical recorded prices ranging from approximately £17,248 to £42,534. Checkatrade
Those figures are useful as a local benchmark, but they should not be treated as the cost of every extension. A small, straightforward rear extension is completely different from a 40 m² kitchen extension with large structural openings, premium glazing and a high-specification kitchen.
For larger projects, the national 2026 benchmark of around £1,800–£3,000 per m² remains a useful starting point for completed extension space.
At Tholos Architects, we help homeowners develop extensions around both the property and the available budget, rather than simply choosing a size and hoping the final quotation fits.
Extension Cost Derby explained
Derby Extension Cost per Square Metre
For early budgeting in Derby, around:
£1,800–£3,000 per m²
is a sensible broad starting range for a completed standard extension.
Current national 2026 guidance gives an average around £2,400 per m², with typical finished extension costs ranging from approximately £1,800 to £3,000 per m².
The actual Derby cost will depend on:
- Size
- Ground conditions
- Structural design
- Roof
- Glazing
- Kitchen or bathroom
- Site access
- Specification
A simple extension may sit toward the lower end.
A high-specification project can exceed the upper end.
Typical Extension Costs in Derby
Current local Derby data gives:
| Derby Extension Project | Current Local Benchmark |
|---|---|
| Lower-end extension project | Around £17,248 |
| Average extension project | Around £27,218 |
| Upper typical local project | Around £42,534 |
These are recorded local averages across a range of extension types and sizes rather than prices for one standard extension.
For larger projects, floor area becomes more useful as an early budgeting tool.
Extension Cost by Size in Derby
Using the wider 2026 benchmark of £1,800–£3,000 per m², indicative construction budgets are:
| Extension Size | Indicative Cost |
|---|---|
| 15 m² | £27,000–£45,000 |
| 20 m² | £36,000–£60,000 |
| 25 m² | £45,000–£75,000 |
| 30 m² | £54,000–£90,000 |
| 40 m² | £72,000–£120,000 |
| 50 m² | £90,000–£150,000 |
These are broad construction figures rather than quotations.
They also explain why the local Derby average of around £27,000 should not be used as the expected price for every project: larger extensions naturally sit well above it.
Why Derby Extension Costs Vary
Two extensions in Derby can have the same floor area and very different prices.
One might include:
- Simple rectangular footprint
- Standard windows
- Straightforward roof
- Limited structural work
Another might include:
- Large steel frame
- Bifold or sliding doors
- Rooflights
- New kitchen
- Utility room
- Extensive internal remodelling
The second project may cost tens of thousands of pounds more despite adding the same amount of new floor space.
Single-storey Extension Cost Derby
Single-storey extensions are one of the most common types of domestic project.
They can be used for:
- Kitchen-diners
- Family rooms
- Utility rooms
- Home offices
- Additional bedrooms
Current UK guidance places single-storey extensions broadly around:
£1,800–£3,000 per m². FMB
For a typical 20 m² extension, that suggests roughly:
£36,000–£60,000
before any particularly expensive kitchen, glazing or structural work.
20 m² Extension Cost Derby
For a 20 m² extension, a reasonable early construction budget is around:
£36,000–£60,000
based on the current £1,800–£3,000 per m² benchmark.
A relatively straightforward project may fall toward the lower end.
A project involving:
- New kitchen
- Large rear opening
- Structural steel
- Significant glazing
can quickly move toward the upper end.
30 m² Extension Cost Derby
For 30 m², a broad early allowance would be around:
£54,000–£90,000
This is often a more realistic way to budget for a meaningful kitchen or family-room extension than relying on local average project values alone.
40 m² Extension Cost Derby
For around 40 m²:
£72,000–£120,000
is a useful broad construction range.
Projects at this scale may also contain more:
- Structural work
- Kitchen specification
- Heating
- Flooring
- Electrical work
so the final project cost can exceed the simple floor-area calculation.
Extension Cost Derby
Rear Extension Cost Derby
Rear extensions are popular because they can improve both floor area and the relationship between the house and garden.
They are often used to create:
- Kitchen-diners
- Family rooms
- Open-plan living areas
Cost depends heavily on:
- Width
- Depth
- Structural opening
- Glazing
- Roof form
- Internal remodelling
A modest rear extension may sit near the lower part of the £1,800–£3,000 per m² range.
A large kitchen extension with extensive structural alterations can cost significantly more.
Side Extension Cost Derby
A side extension can provide useful additional floor area where the plot allows.
It may create:
- Larger kitchen
- Utility room
- Office
- Extra bedroom
- Additional living room
Current 2026 side-return guidance gives a broad range of approximately £1,500–£4,500 per m², with around £3,000 per m² as an average across projects and locations.
Derby projects would usually avoid the London premium at the top of that range, although design complexity still matters.
Side-return Extension Cost Derby
Side-return extensions are more common on older terraced or semi-detached homes.
They can appear small but often involve:
- Drainage alterations
- Boundary construction
- Structural steel
- Roof glazing
- Kitchen remodelling
Current guidance puts a small single-storey side return around £30,000–£45,000, with an average around £37,500
Wraparound Extension Cost Derby
A wraparound extension combines:
- Rear extension
- Side extension
and can completely transform the ground floor.
Because it involves a larger footprint and often more:
- Foundations
- Structure
- Roof
- Drainage
it usually costs more than a straightforward rear extension.
Kitchen Extension Cost Derby
Kitchen extensions can cost more than basic room extensions because the kitchen itself can be one of the largest individual budget items.
Additional costs may include:
- Units
- Worktops
- Appliances
- Plumbing
- Electrical circuits
- Extraction
- Island
- Lighting
The construction and kitchen should therefore be budgeted together.
Double-storey Extension Cost Derby
A double-storey extension costs more overall but can create better value per square metre because both floors share:
- Foundations
- Groundworks
- Roof footprint
Current 2026 guidance places double-storey extension costs around:
£1,650–£3,000 per m²
depending on quality, size and location.
For a 60 m² total extension, that equates broadly to:
£99,000–£180,000
before certain fixtures and fittings, depending on the pricing basis used.
Semi-detached Extension Cost Derby
Derby has many semi-detached properties where side and rear extensions can work particularly well.
Benefits can include:
- Better side access
- More flexible footprint
- Larger garden width
The cost still depends on:
- Existing house
- Foundations
- Structure
- Glazing
- Specification
The £1,800–£3,000 per m² national benchmark remains a useful starting point.
Terraced House Extension Cost Derby
Terraced properties can sometimes cost slightly more to build on because access is more restricted.
Materials and waste may need to pass:
- Through the property
- Through a narrow alley
- By manual handling
This increases labour.
Party-wall matters may also be more relevant where neighbouring properties sit close to the proposed work.
Detached House Extension Cost Derby
Detached homes often provide easier access for:
- Materials
- Excavation equipment
- Waste removal
That can simplify construction logistics.
However, detached properties may also have:
- Larger extension footprints
- Larger glazing
- More ambitious layouts
so the total budget may still be substantial.
Extension Foundations Cost Derby
Foundations depend on:
- Ground conditions
- Nearby trees
- Existing drainage
- Existing structures
A builder may initially price standard foundations.
If excavation reveals unexpected ground conditions, costs can rise.
That is one reason contingency remains important.
Structural Work
Extension projects frequently require structural work where the existing house is opened into the new space.
This may involve:
- Steel beams
- Columns
- Padstones
- Structural frames
- Temporary support
The size of the opening can have a significant impact on cost.
Removing the Rear Wall
A large opening between the house and extension may look simple on a floor plan.
Structurally, it can require:
- Large beam
- Columns
- Support to upper storey
- Temporary works
Reducing the opening slightly can sometimes simplify the structure considerably.
Structural Engineer Cost
Structural engineering is usually a separate professional cost unless expressly included in another package.
It may cover:
- Beams
- Columns
- Foundations
- Roof support
- Structural calculations
Drainage Costs
Existing drainage can affect both extension layout and foundations.
Work may require:
- Moving drains
- New inspection chambers
- Soil-pipe alterations
- New rainwater drainage
Investigating drainage before construction can help reduce uncertainty.
Roof Costs
The roof design can materially affect the budget.
Options may include:
- Flat roof
- Pitched roof
- Lean-to roof
- Combination roof
A simple roof is generally cheaper than one involving:
- Multiple junctions
- Complex geometry
- Extensive structural glazing
Rooflights
Rooflights can improve daylight in deeper extension plans.
Their cost depends on:
- Number
- Size
- Brand
- Opening type
Standard rooflights are normally more economical than bespoke roof glazing.
Sliding and Bifold Doors
Large rear doors are popular in extensions.
Their price depends on:
- Width
- Number of panels
- Aluminium or other framing
- Glass specification
They can also increase structural cost because a larger opening needs more support above.
extension cost in Derby
Open-plan Extension Cost Derby
Many extension projects are really two projects in one:
- Build the extension
- Remodel the existing ground floor
Creating a large open-plan space may involve removing several walls.
This can increase:
- Steelwork
- Electrical work
- Flooring
- Decoration
Internal Remodelling Costs
A smaller extension combined with sensible internal remodelling can sometimes create a better result than simply building more floor area.
Changes might include:
- New door positions
- Utility room
- Downstairs WC
- Better storage
- Better storage Improved circulation
Planning Permission in Derby
Whether planning permission is required depends on the property and the proposal.
Some domestic extensions may fall within permitted development rights.
Others require planning permission.
Factors can include:
- Extension size
- Height
- Position
- Previous alterations
- Property type
- Local restrictions
The specific property should always be checked.
Building Regulations in Derby
Applicable Building Regulations requirements normally apply even where planning permission is not needed.
These can cover:
- Structure
- Foundations
- Insulation
- Fire safety
- Drainage
- Ventilation
- Glazing
- Electrical work
Architectural Drawing Costs
Architectural fees should be considered separately from the construction cost.
The service may include:
- Measured survey foundations
- Existing drawings
- Proposed design
- Planning drawings
- Building Regulations drawings
- Technical information
VAT
One of the easiest mistakes is comparing one extension price that includes VAT with another that does not.
Checkatrade’s current £1,800–£3,000 per m² house-extension range is quoted excluding VAT
Always check:
- Builder quotation
- Supplier prices
- Professional fees
individually.
Hidden Extension Costs
A Derby extension budget may also need to account for:
- Planning
- Building Control
- Engineer
- Party-wall costs where relevant
- Scaffolding
- Waste
- Flooring
- Decoration
- Landscaping
- VAT
- Contingency
Project Contingency
A sensible contingency should remain available for unexpected costs.
Around:
10%
is a useful starting point for many straightforward projects.
Older or more structurally complex properties may justify more.
extension cost in Derby
Can You Build an Extension in Derby for £30,000?
Potentially, yes.
Current local Checkatrade data gives around £27,218 as the average recorded extension project in Derby.
But £30,000 is more realistic for:
- Smaller extension
- Straightforward structure
- Standard specification
- Limited internal remodelling
A larger kitchen extension will normally require more.
Can You Build an Extension in Derby for £50,000?
Yes.
£50,000 can support a meaningful extension depending on size and complexity.
Using the current £1,800–£3,000 per m² benchmark, that corresponds broadly to:
- Around 27 m² at £1,800 per m²
- Around 17 m² at £3,000 per m²
before separately considering expensive specification items or excluded fees.
Can You Build an Extension in Derby for £75,000?
Yes.
A £75,000 construction budget gives considerably more flexibility for:
- Larger extension
- Structural opening
- Better glazing
- Kitchen work
But it should still be supported by a proper scope and builder quotation.
Can You Build an Extension in Derby for £100,000?
Yes.
£100,000 can support a substantial extension in Derby.
Depending on specification, this may allow:
- Large single-storey extension
- Major kitchen-diner
- Significant internal remodelling
But the complete project budget may need to exceed £100,000 once professional fees, VAT and contingency are included.
How to Reduce Extension Costs in Derby
The biggest savings often come from design decisions.
Consider:
- Keep the footprint efficient
- Use a simple roof
- Avoid unnecessary structural spans
- Limit bespoke glazing
- Keep drainage changes manageable
- void moving services without a reason
- Use standard product sizes
Do Not Automatically Build the Maximum Size
More floor area is not always better value.
A slightly smaller extension can sometimes provide:
- Better garden
- More daylight
- Lower cost
- Simpler structure
A well-designed 25 m² extension may work far better than a poorly planned 35 m² one.
Design the Kitchen Early
If the extension is mainly for a new kitchen, plan the kitchen while the architecture is being developed.
Consider:
- Island
- Cabinet runs
- Dining table
- Circulation
- Storage
- Garden doors
You may discover that the project needs less additional floor area than expected.
Extension cost in Derby
Get Comparable Builder Quotes
Once the project is sufficiently developed, suitable Derby builders should ideally price the same:
- Drawings
- Structural information
- Specification
- Scope
Otherwise, the cheapest quotation may simply contain more exclusions.
Derby Extension Budget Checklist
Your total project budget may need to include:
- Construction
- Foundations
- Structure
- Drainage
- Roof
- Windows and doors
- Kitchen
- Plumbing
- Electrical work
- Heating
- Flooring
- Decoration
- Architectural fees
- Structural engineer
- Planning
- Building Control
- External works
- VAT
- Contingency
The local average construction figure should therefore never be treated automatically as the finished total project cost.
How Tholos Can Help With Your Derby Extension
The aim of good extension design is not simply to add as many square metres as possible.
At Tholos Architects, we can consider:
- Existing house
- Layout
- Extension size
- Structure
- Natural light
- Kitchen
- Planning
- Budget
together.
That allows the extension to be designed around how the house actually needs to work and how much you realistically want to spend.
Client experience
"
Lorem ipsum dolor sit amet, consectetur adipiscing elit. We had a vision for our home but no idea how to realise it. Tholos Interiors took complete ownership of the project — every detail was considered, every decision explained. The result exceeded everything we had imagined.
– Lawrence Ipsum, Homeowner · London –
Frequently Asked Questions
How much does an extension cost in Derby?
Current local 2026 Checkatrade data puts the average recorded Derby extension project at around £27,218, with a typical range of approximately £17,248–£42,534
How much does an extension cost per m² in Derby?
For early budgeting, approximately £1,800–£3,000 per m² is a useful current benchmark for a completed extension
How much does a 20 m² extension cost in Derby?
Around £36,000–£60,000 is a useful broad construction estimate using current per-square-metre guidance.
How much does a 30 m² extension cost in Derby?
Approximately £54,000–£90,000 is a reasonable broad early-stage allowance.
Use Derby Costs, Not London Costs
One advantage of building in Derby is that you generally avoid the substantial regional premium associated with London and parts of the South East.
Current local data gives an average Derby extension project around:
£27,218
with recorded typical project values between approximately:
£17,248 and £42,534. Checkatrade
For larger projects, around:
£1,800–£3,000 per m²
remains a more useful budgeting benchmark. Checkatrade
The right figure ultimately depends on the size, structure, specification and existing property.
At Tholos Architects, we can help develop an extension that balances the additional space you want with a realistic Derby project budget.
Disclaimer
This article is part of a series created by our dynamic marketing team for informational purposes only. While we strive to review all content thoroughly, occasional oversights may occur, even after publication. Therefore, we cannot accept liability for any interpretations or use of the information provided. For the most up-to-date information or to report any discrepancies, please contact us at hello@tholos-architects.com.
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