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How Much Does a House Extension Cost in Durham?
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How Much Does a House Extension Cost in Durham?
The cost of a house extension in Durham depends on the size of the project, the type of extension, the existing property and the level of specification.
Current local Checkatrade data puts the average extension project in Durham at around £32,709, with typical recorded prices ranging from approximately £20,085 to £52,106. Checkatrade
That gives a useful local benchmark, but it should not be treated as the expected cost of every extension.
A small rear extension with a straightforward roof and limited internal work is very different from a large kitchen extension involving:
- Structural steelwork
- Large glazed doors
- New kitchen
- Utility room
- Underfloor heating
- Extensive internal remodelling
For larger projects, current 2026 UK guidance puts a typical single-storey extension at around £1,800–£3,000 per m². FMB
At Tholos Architects, we help homeowners develop extensions around the existing property, the space they actually need and a realistic construction budget.
Extension Cost Durham explained
Durham Extension Cost per Square Metre
For early budgeting in Durham, around:
£1,800–£3,000 per m²
is a sensible broad starting point for a standard single-storey extension.
Federation of Master Builders guidance currently gives this range as the UK average, while noting that location, specification and complexity can significantly affect the final cost. FMB
The actual cost of your Durham extension may depend on:
- Extension size
- Property type
- Structural work
- Ground conditions
- Roof design
- Glazing
- Kitchen or bathroom
- Site access
- Internal remodelling
- Quality of finishes
A relatively simple extension may sit toward the lower end.
A project with premium finishes or extensive structural work can exceed the upper end.
Typical Extension Costs in Durham
Current local Durham pricing data gives:
| Durham Extension Project | Current Local Benchmark |
|---|---|
| Lower typical project | Around £20,085 |
| Average extension project | Around £32,709 |
| Upper typical project | Around £52,106 |
These figures reflect local extension projects of different sizes and types rather than one standard extension.
For larger projects, calculating a broad cost by floor area can provide a more useful starting point.
Extension Cost by Size in Durham
Using the current £1,800–£3,000 per m² single-storey benchmark:
| Extension Size | Indicative Construction 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 early-stage construction figures rather than quotations. FMB
The final project budget may also need to include:
- Architectural fees
- Structural engineer
- Planning
- Building Control
- Kitchen
- Bathrooms
- External works
- VAT
- Contingency
Why Durham Extension Costs Vary
Two Durham extensions with exactly the same floor area can cost very different amounts.
One might involve:
- Simple rectangular footprint
- Standard roof
- Standard windows
- Limited structural work
- Basic finishes
Another might include:
- Large steel frame
- Wide opening into the existing house
- Sliding doors
- Rooflights
- New kitchen
- Utility room
- Premium flooring
The number of square metres is therefore only one part of the cost.
Single-storey Extension Cost Durham
Single-storey extensions are one of the most common ways to create additional space.
They can be used for:
- Kitchen-diners
- Family rooms
- Utility rooms
- Home offices
- Additional bedrooms
- Accessible accommodation
Current FMB guidance puts the average UK single-storey extension at around:
£1,800–£3,000 per m². FMB
For a 20 m² extension, that suggests around:
£36,000–£60,000
before allowing separately for particularly expensive kitchens, glazing or other specialist work.
20 m² Extension Cost Durham
For a 20 m² extension in Durham, a useful broad starting range is:
£36,000–£60,000
using current UK single-storey extension guidance. FMB
A project toward the lower end would normally need to remain relatively straightforward.
Costs can rise where the extension includes:
- Kitchen
- Large structural opening
- Bespoke glazing
- Extensive internal work
30 m² Extension Cost Durham
For a 30 m² extension, a broad early construction budget would be approximately:
£54,000–£90,000
At this scale, the project may also involve more:
- Electrical work
- Heating
- Flooring
- Kitchen specification
- Structural steel
so the total budget may exceed the simple square-metre calculation.
40 m² Extension Cost Durham
For approximately 40 m²:
£72,000–£120,000
is a useful broad construction range.
A larger extension can sometimes provide better value per square metre because some fixed costs are spread across a greater area.
However, premium specification can quickly offset that advantage.
Extension Cost Durham
Rear Extension Cost Durham
Rear extensions are one of the most popular ways to enlarge a home.
They are often used to create:
- Kitchen-diners
- Family rooms
- Open-plan living areas
- Better connection to the garden
Cost depends on:
- Width
- Depth
- Structural opening
- Roof form
- Glazing
- Internal remodelling
A straightforward rear extension may sit toward the lower end of current cost-per-square-metre guidance.
Side Extension Cost Durham
Where the property has enough side space, a side extension can create:
- Larger kitchen
- Utility room
- Office
- bedroom
- Additional living room
Side extensions can also work particularly well on semi-detached and detached houses.
The overall cost depends on how the new structure connects to the existing house.
Side-return Extension Cost Durham
Side-return extensions can be particularly useful on older terraced and semi-detached properties.
They often involve:
- Boundary construction
- Drainage alterations
- Structural steel
- Rooflights
- Kitchen remodelling
Current 2026 guidance puts a small single-storey side return at around £30,000–£45,000, averaging approximately £37,500.
Wraparound Extension Cost Durham
A wraparound extension combines rear and side extension space.
It can create a substantial ground-floor transformation but typically requires more:
- Foundations
- Walls
- Roof
- Drainage
- Structural work
than a straightforward rear extension.
Kitchen Extension Cost Durham
Kitchen extensions can cost significantly more than basic room extensions because the project may also require:
- Kitchen units
- Worktops
- Appliances
- Plumbing
- Electrical circuits
- Lighting
- Extraction
- Kitchen island
The construction and the kitchen should therefore be budgeted together.
Double-storey Extension Cost Durham
A double-storey extension creates space on two floors.
Although it costs more overall than a single-storey project, it can provide good value per square metre because both floors share:
- Foundations
- Groundworks
- Roof footprint
Current 2026 guidance puts double-storey extensions around:
£1,650–£3,000 per m²
depending on quality, size and location.
For a total extension area of 60 m², that would broadly suggest:
£99,000–£180,000
before some fixtures, finishes and professional costs are considered.
Semi-detached Extension Cost Durham
Semi-detached houses can work well with:
- Rear extensions
- Side extensions
- Double-storey extensions
- Over-garage extensions
Side access can sometimes make construction easier because materials and waste do not need to pass through the house.
However, cost still depends on:
- Existing structure
- Extension size
- Ground conditions
- Specification
Terraced House Extension Cost Durham
Terraced houses can introduce additional construction challenges.
Potential issues include:
- Restricted rear access
- Narrow passages
- Materials carried through the house
- Difficult waste removal
- Party-wall considerations
That can increase labour even where the actual extension is relatively modest.
Detached House Extension Cost Durham
Detached houses may provide better access for:
- Deliveries
- Excavation
- Machinery
- Waste removal
This can simplify construction logistics.
However, detached properties often allow larger extensions, which means the overall construction budget can still be substantial.
Foundations
Foundation cost depends on:
- Ground conditions
- Nearby trees
- Existing drainage
- Existing structures
- Extension loads
Builders may initially price relatively standard foundation assumptions.
If excavation reveals different conditions, the cost can increase.
Ground Conditions
Unexpected ground conditions can require:
- Deeper foundations
- Additional excavation
- More concrete
- Revised structural design
This is one reason project contingency is important.
Structural Work
Extensions often involve substantial alterations to the existing house.
Creating a wide opening between the original building and the new extension may require:
- Steel beams
- Columns
- Padstones
- Structural frames
- Temporary support
The structural design can become a significant cost driver.
Removing the Rear Wall
A large rear opening may look simple on an architectural plan.
Structurally, it may need to support:
- Upper floor
- Rear wall
- Roof
Sometimes retaining a small wall section or column can simplify the structural solution considerably.
Structural Engineer Cost
A structural engineer may need to design:
- Beams
- Columns
- Foundations
- Roof support
- Structural calculations
Their fees should be included separately unless expressly part of another service.
Drainage Costs
Existing drainage can affect both the extension layout and construction cost.
Work may involve:
- Moving drains
- New inspection chambers
- New soil connections
- Rainwater drainage
Investigating existing drainage before construction can help reduce uncertainty.
Roof Costs
The roof form can have a significant effect on extension cost.
Options might include:
- Flat roof
- Pitched roof
- Lean-to roof
A simple roof usually gives greater cost certainty.
More complex roof geometry can increase:
- Labour
- Materials
- Flashings
- Structural work
Rooflights
Rooflights are commonly used to bring natural light into deeper extension spaces.
Their cost depends on:
- Size
- Number
- Brand
- Fixed or opening
- Installation
Standard rooflights generally cost less than bespoke roof glazing.
Sliding and Bifold Doors
Large rear doors can create a strong connection to the garden.
Their cost depends on:
- Width
- Frame material
- Number of panels
- Glass specification
They can also increase structural costs because the opening above needs to be supported.
extension cost in Durham
Open-plan Extension Cost Durham
Many homeowners use an extension to create a large kitchen-dining-living space.
This often involves removing walls from the existing house.
That may increase:
- Steelwork
- Temporary support
- Electrical work
- Flooring
- Decoration
The cost can therefore be much higher than simply constructing an enclosed extension of the same size.
Internal Remodelling Costs
An extension can also trigger wider changes to the existing house.
These might include:
- New door positions
- Utility room
- Downstairs WC
- Better storage
- New circulation
- Larger kitchen
Sometimes a smaller extension combined with better internal planning can achieve more than simply building additional floor area.
Planning Permission in Durham
Not every extension requires planning permission.
Some may fall within permitted development rights if they meet the relevant conditions.
Others require a householder planning application.
Factors can include:
- Size
- Height
- Position
- Previous alterations
- Property type
- Local restrictions
The planning position should always be checked for the specific property.
Building Regulations in Durham
Applicable Building Regulations requirements normally apply regardless of whether planning permission is needed.
These may cover:
- Foundations
- Structure
- Fire safety
- Insulation
- Ventilation
- Drainage
- Glazing
- Electrical work
Architectural Drawing Costs
Architectural services may include:
- Measured survey
- Existing drawings
- Proposed design
- Planning drawings
- Building Regulations drawings
- Technical information
These fees should be considered separately from the construction cost.
Kitchen and Bathroom Costs
How you intend to use the new extension has a major impact on price.
A simple office or playroom is normally cheaper than a:
- Kitchen
- Utility room
- Bathroom
because those rooms require more:
- Plumbing
- Electrical work
- Fixtures
- Finishes
Current double-storey extension guidance, for example, gives around £15,000 extra for a kitchen and around £6,750 for a bathroom as broad additional-cost benchmarks.
VAT
Always check whether the extension quotation includes VAT.
A figure of:
£60,000 excluding VAT
is materially different from:
£60,000 including VAT.
This should be checked when comparing:
- Builder quotation
- Supplier prices
- Professional fees
Hidden Extension Costs
The complete Durham extension budget may also need to include:
- Architectural fees
- Structural engineer
- Planning
- Building Control
- Party-wall costs where relevant
- Scaffolding
- Waste removal
- Kitchen
- Flooring
- Decoration
- Landscaping
- VAT
- Contingency
Project Contingency
A contingency should remain available for genuine unexpected costs.
Around: 10%
is a useful starting point for many relatively straightforward projects.
Older properties or work involving significant structural alteration may justify a larger reserve.
extension cost in Durham
Can You Build an Extension in Derby for £30,000?
Potentially.
Current local data gives around £32,709 as the average extension cost in Durham, with the lower end of typical projects starting around £20,085. Checkatrade
A £30,000 budget is more realistic for:
- Smaller footprint
- Straightforward structure
- Standard specification
- Limited internal remodelling
A substantial kitchen extension is likely to require more.
Can You Build an Extension in Durham for £50,000?
Yes, depending on the project.
Using the current £1,800–£3,000 per m² benchmark, £50,000 broadly corresponds to:
- Around 27 m² at £1,800 per m²
- Around 17 m² at £3,000 per m²
before particularly expensive specification items or separately excluded costs are considered.
Can You Build an Extension in Durham for £75,000?
Yes.
A £75,000 construction budget gives greater flexibility for:
- Larger floor area
- Structural opening
- New kitchen
- Better glazing
- Internal remodelling
The actual project should still be costed from developed drawings and specifications.
Can You Build an Extension in Durham for £100,000?
Yes.
£100,000 can support a substantial extension in Durham.
Depending on the project, this might include:
- Large kitchen-diner
- Major rear extension
- Significant ground-floor remodelling
- Wraparound extension
But the complete project budget may need to exceed £100,000 once professional fees, VAT and contingency are included.
Can a Durham Extension Cost More Than £150,000?
Absolutely.
Larger or higher-specification projects can exceed £150,000 where they combine:
- Significant floor area
- Structural steelwork
- Premium glazing
- High-end kitchen
- Extensive internal remodelling
- Premium finishes
The local average of £32,709 should therefore never be treated as a maximum price.
How to Reduce Extension Costs in Durham
Some of the biggest savings come from design decisions.
Consider:
- Keep the footprint efficient
- Use a simple roof
- Avoid unnecessary structural spans
- Use standard glazing sizes
- Keep drainage changes manageable
- Avoid unnecessary service relocation
- Control specification early
Do Not Automatically Build the Maximum Size
More floor area does not automatically produce a better home.
A smaller extension may provide:
- Better daylight
- More garden
- Lower construction cost
- Simpler structure
when combined with intelligent internal remodelling.
The aim should be useful space rather than maximum square metres.
Keep the Structure Simple
Large column-free openings look attractive but can require expensive steelwork.
Sometimes retaining:
- A small column
- Short wall section
- Slightly narrower opening
can significantly simplify the structural solution without affecting how the room works.
Extension cost in Durham
Get Comparable Builder Quotes
Suitable Durham builders should ideally price the same:
- Architectural drawings
- Structural information
- Specification
- Scope
Otherwise, the cheapest quotation may simply contain more exclusions.
Durham Extension Budget Checklist
Your overall project budget may need to include:
- Construction
- Foundations
- Structural work
- Drainage
- Roof
- Windows and doors
- Kitchen
- Plumbing
- Electrical work
- Heating
- Flooring
- Decoration
- Architectural fees
- Structural engineer
- Planning
- Building Control
- External works
- VAT
- Contingency
The builder’s construction quote should not automatically be treated as the complete project budget.
How Tholos Can Help With Your Durham Extension
A successful extension should improve the way the whole house works.
At Tholos Architects, we can consider:
- Existing layout
- Extension size
- Structure
- Natural light
- Kitchen
- Planning
- Budget
together from the beginning.
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 Durham?
Current local data puts the average Durham extension project at around £32,709, with typical prices starting at approximately £20,085 and reaching around £52,106.
How much does an extension cost per m² in Durham?
Around £1,800–£3,000 per m² is a useful 2026 starting range for a standard single-storey extension.
How much does a 20 m² extension cost in Durham?
Approximately £36,000–£60,000 is a useful broad early-stage construction estimate.
How much does a 30 m² extension cost in Durham?
Around £54,000–£90,000 is a useful broad starting range.
Budget for the Actual Durham Project
Current local pricing gives an average Durham extension cost of approximately:
£32,709
with typical recorded projects ranging from around:
£20,085 to £52,106. For larger extensions, however, the current:
£1,800–£3,000 per m²
single-storey benchmark is often a more useful starting point. FMB
The right figure depends on:
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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