Understanding the costs involved in a home extension is crucial for planning your project. This comprehensive guide breaks down 2026 prices for various extension types across Devon.

Average Extension Costs Overview

Here's a quick reference for typical extension costs in Devon:

Single-storey extension: £1,800 - £2,500 per m²
Two-storey extension: £1,600 - £2,200 per m²
Kitchen extension: £25,000 - £60,000
Loft conversion: £30,000 - £60,000
Garage conversion: £15,000 - £35,000

These are guide prices - your actual costs will depend on numerous factors we'll explore in detail.

Factors Affecting Extension Costs

1. Size and Complexity

The most significant cost factor is the size of your extension:

Small (10-15m²): £18,000 - £37,500
Medium (20-30m²): £36,000 - £75,000
Large (40m²+): £72,000 - £100,000+

Complex designs with unusual shapes, multiple levels, or intricate details cost more than simple rectangular extensions.

2. Specification and Finishes

Your choice of materials and finishes dramatically impacts costs:

Budget Specification

Standard double glazing
Basic kitchen units
Laminate worktops
Standard bathroom fittings
Basic floor tiles

Mid-Range Specification

High-performance double glazing
Good quality kitchen units
Quartz or granite worktops
Quality bathroom fixtures
Porcelain tiles

Premium Specification

Triple glazing or large bi-fold doors
Bespoke kitchen cabinetry
Premium stone worktops
Designer bathroom fittings
Natural stone or high-end tiles

The difference between budget and premium can add 30-50% to costs.

3. Location in Devon

Costs vary slightly across Devon:

Plymouth: Generally competitive pricing due to good contractor availability

Torquay & Torbay: Coastal location may increase material transport costs slightly

Exeter: City centre locations may have access constraints affecting costs

Rural Devon: May incur additional costs for material delivery and contractor travel

4. Ground Conditions

Your site's ground conditions affect foundation costs:

Good ground: Standard strip foundations
Poor ground: May require deeper or reinforced foundations
Sloping sites: Additional groundwork and retaining walls
Trees nearby: Root protection measures required

Ground investigation can identify potential issues early.

5. Access and Site Constraints

Difficult access increases costs:

Narrow side passages
No vehicle access to rear
Terraced properties with limited access
Conservation areas with material restrictions

Detailed Cost Breakdown by Extension Type

Single-Storey Rear Extension

Typical Size: 4m x 6m (24m²)

Cost Range: £43,000 - £60,000

Includes:

Foundations and structural work
Roof (flat or pitched)
External walls and insulation
Windows and doors
Internal finishes
Electrics and heating
Building regulations fees

Additional Costs:

Kitchen installation: £5,000 - £25,000
Bi-fold doors (instead of standard): £3,000 - £8,000
Underfloor heating: £1,500 - £3,000
Roof lantern: £2,500 - £6,000

Two-Storey Extension

Typical Size: 4m x 6m (48m² total - 24m² per floor)

Cost Range: £75,000 - £105,000

Why It's More Cost-Effective:

Shared foundations and roof
Cost per m² lower than single-storey
Adds more space for similar ground footprint

Includes:

All structural work for both floors
Stairs if required
Two sets of windows and internal finishes
Extended heating and electrical systems

Kitchen Extension

Typical Size: 3m x 5m (15m²)

Cost Range: £25,000 - £60,000

Budget Breakdown:

Building work: £20,000 - £35,000
Kitchen units and appliances: £5,000 - £15,000
Worktops: £1,000 - £5,000
Flooring: £1,000 - £3,000
Lighting and electrics: £1,500 - £2,500

Popular Additions:

Bi-fold or sliding doors: £3,000 - £8,000
Roof lantern: £2,500 - £6,000
Underfloor heating: £1,200 - £2,500

Loft Conversion

Cost Range: £30,000 - £60,000

Depends On:

Dormer loft conversion: £35,000 - £50,000
Hip-to-gable conversion: £40,000 - £55,000
Mansard conversion: £45,000 - £60,000
Velux conversion: £30,000 - £40,000

Includes:

Structural alterations
Dormer construction (if applicable)
Stairs
Insulation and plasterboard
Electrics and heating
Bathroom if required: add £5,000 - £12,000

Garage Conversion

Cost Range: £15,000 - £35,000

Typical Costs:

Basic conversion: £15,000 - £20,000
Mid-range: £20,000 - £28,000
High-end: £28,000 - £35,000

Work Involved:

Removing garage door and building wall
Insulation and damp-proofing
New windows and door
Electrics and heating
Internal finishes
Flooring

Additional Costs:

En-suite bathroom: £5,000 - £10,000
Bi-fold doors instead of wall: £3,000 - £6,000

Hidden Costs to Consider

Many homeowners underestimate these additional expenses:

Professional Fees

Architect/designer: £1,500 - £5,000 (or 8-12% of build cost)
Structural engineer: £500 - £1,500
Planning application: £206 (if required)
Building regulations: £800 - £1,500
Party wall agreement: £700 - £1,500 (if applicable)

Site Preparation

Demolition work: £1,000 - £3,000
Tree removal: £500 - £2,000
Drainage alterations: £1,500 - £4,000
Service relocations: £500 - £2,000

Temporary Measures

Temporary kitchen: £500 - £1,500
Storage for furniture: £100 - £300 per month
Alternative accommodation: Variable

Finishing Touches

Decorating: £1,500 - £5,000
New furniture: £2,000 - £10,000
Landscaping: £2,000 - £8,000
Driveway repairs: £1,000 - £3,000

How to Reduce Extension Costs

1. Simple Design

Rectangular shapes are more cost-effective than complex layouts.

2. Standard Sizes

Use standard window and door sizes rather than bespoke.

3. Timing

Building in spring/summer can be slightly cheaper and faster.

4. Specification Choices

Mix budget and premium items - splurge on key features, save on hidden elements.

5. Do Some Work Yourself

Decorating, landscaping, and some finishing work can be DIY.

6. Get Multiple Quotes

Compare at least three detailed quotes from reputable builders.

Financing Your Extension

Savings

The most cost-effective option if you have sufficient funds.

Remortgage

Release equity from your property:

Typically lower interest rates
Spread cost over mortgage term
May incur arrangement fees

Home Improvement Loan

Unsecured personal loan:

Quick to arrange
No property valuation needed
Higher interest rates than remortgage

Equity Release

For older homeowners:

Access property value without moving
No monthly repayments
Reduces inheritance value

Return on Investment

Understanding the value an extension adds helps justify the cost:

Kitchen Extension

Cost: £40,000
Value Added: £45,000 - £55,000
ROI: 112% - 137%

Loft Conversion

Cost: £45,000
Value Added: £50,000 - £65,000
ROI: 111% - 144%

Two-Storey Extension

Cost: £85,000
Value Added: £90,000 - £110,000
ROI: 106% - 129%

Note: ROI varies by location, property type, and local market conditions.

Getting an Accurate Quote

For a reliable cost estimate, provide builders with:

Detailed plans: Design plans if available
Specification list: Materials and finishes you want
Site photos: Help builders assess access and conditions
Timeline: When you want to start and complete
Budget indication: Helps builders suggest appropriate specifications

Our Transparent Pricing Approach

At NL Elite Builders, we provide:

Detailed written quotes: Itemised breakdown of all costs
Fixed-price contracts: No hidden extras
Payment schedules: Clear milestones and payment terms
Variation procedures: How changes are priced and approved
Warranty coverage: What's included in our guarantee

Conclusion

Home extension costs in Devon vary significantly based on size, specification, and complexity. Budget £1,800 - £2,500 per m² for single-storey extensions, with additional costs for professional fees, finishes, and contingencies.

The key to managing costs is:

Detailed planning before starting
Clear specification of materials
Realistic budget with contingency
Working with experienced builders

Ready to discuss your extension project? Contact us for a free, no-obligation quote. We'll provide a detailed breakdown of costs and help you make informed decisions about your investment.