Design and Build | Estimated Overall Costs (Typical UK Scenario)
- JL
- 1 day ago
- 5 min read
A detailed cost breakdown for a typical two-storey extension in the UK that adds an open-plan kitchen & dining room at the rear of your property, tailored for 2025–2026 pricing.
For this example, let’s assume you’re adding:
A 5 m deep rear extension across the width of the house
Rough footprint: 20–25 m² ground floor
Upper floor roughly matching that footprint
Includes solid construction, glazing, stair connection and basic kitchen fit-out
Component | Estimated Range (GBP) | Notes |
Main build (structural shell) | £70,000 – £110,000 | Includes brick/ blockwork, roof, floors, windows & doors |
Professional fees (architect, engineer) | £7,000 – £15,000 | 7–15% of build cost |
Planning & approvals | £500 – £3,000 | Planning, building regs & surveys |
Utilities & services (M&E) | £6,000 – £12,000 | Electrics, plumbing, heating |
Kitchen fitting & appliances | £8,000 – £30,000 | Dependent on quality/specification |
Contingency (10–15%) | £8,000 – £18,000 | Always budget extra for surprises |
Total Typical Cost | £100,000 – £180,000+ | VAT (20%) may apply on elements (unless exempt) |
Breakdown by Key Budget Categories.
Here’s how typical extension money is usually spent:
1. Main Build - Structural Shell
£70,000 – £110,000 This is the largest part of the budget and includes:
Site set-up, scaffolding, demolition if needed
Foundations and groundworks
Brick/block walls, floors, roof structure
Windows & external doors
Roof finish and drainage
For two-storey builds, materials and labour traditionally per m² (excluding finishes) are roughly:
£1,700–£2,500/m² for standard build
This typically accounts for the bulk of materials and labour in your project, often 50–70%+ of total cost.
2. Professional Fees (Design & Engineering)
£7,000 – £15,000This includes:
Architect design & drawings
Structural engineer calculations
Building control submissions
Typical professional fees run around 7–15% of build costs in the UK.
3. Planning, Survey & Permissions
£500 – £3,000Standard charges include:
Planning application: ~£200
Building regulations fee: ~£1,000–£5,000 (varies by value)
Measured survey, tree/ecology reports (if needed)
(Costs vary widely with site conditions and reports needed.)
4. Mechanical & Electrical (M&E) Services
£6,000 – £12,000Covers:
Electrical wiring & sockets
Lighting, safety systems
Heating (rads/underfloor), plumbing runs for kitchen
Hot water and heating controlsTypical services installation can be around several thousand pounds depending on size and complexity.
5. Kitchen Fitting & Appliances
£8,000 – £30,000+A fitted kitchen with integrated appliances, worktops and plumbing can vary significantly:
Budget: c. £8,000
Mid-range: £15,000
High-end: £25,000+This is essentially an optional extra beyond the core build.
6. Contingency
£8,000 – £18,000Always set aside 10–15% of your total project cost to cover:
Unexpected structural issues
Price increases
Design changes mid-buildIndustry guidance strongly recommends this most homeowners underestimate surprises.
Cost Drivers to Expect
Here are some design and build factors that will push costs up or down:
Higher specification finishes — premium flooring, bespoke cabinetry, full-height glazing
Large openings & structural steelwork — especially where you remove load-bearing walls
Site conditions: Hard ground, tree roots, services relocation
Location uplift: London/South East costs typically +10–20%+ due to labour/material pressure
Quick Rule-of-Thumb for Two-Storey Extensions
Core build (excluding kitchen): £1,700–£2,500+ per m²
Add kitchen fitting separately: £8,000–£30,000+
Summary
A well-planned two-storey kitchen/dining extension in the UK in 2025–26 will commonly fall between:
£100,000 – £180,000+ overall
…but remember:
Your design choices, site conditions, and specification levels are the biggest cost drivers.
Always plan for a contingency and include professional fees early in your budget.
The Real Cost of a Home Extension in the UK (2026 Guide)
Most extension budget forecasts are based on cost per square metre (m²). This gives a starting point for early planning before detailed quotes arrive.
Typical Cost per m² (UK Average, 2026)
Basic build: ~£1,900–£2,200/m²
Standard finish: ~£2,200–£2,700/m²
Premium finish: ~£2,700–£3,300/m²(Excluding VAT; VAT adds 20% unless exempted by energy-efficiency rules)
This means that a 20m² single-storey extension in 2026 could cost anywhere from £38,000 to £66,000+ , depending on quality.
Typical Project Examples (These are indicative costs; every project is unique)
Single-Storey Rear Extension
20m²: £40,000–£56,000
30m²: £60,000–£84,000
50m²: £100,000–£140,000(Data based on average UK prices)
Double-Storey Extension
From approx £1,900/m²Double-storey work is often cheaper per m² than single-storey due to shared structural costs (foundations, roofs).
London and High-Cost Areas
In London and the South East, prices can be significantly higher — around £2,500–£4,500/m² — meaning a 30m² extension might reach £75,000–£135,000.
What Drives the Cost?
Size and Scope
Bigger extensions cost more in total — but often less per m² because some fixed costs (e.g., planning, foundations) don’t scale linearly.
Location
Costs in London and the South East are routinely 15–25% above national averages.
Specification and Materials
Simple brickwork and basic finishes will sit at the lower end; high-end glazing, premium flooring, feature roofs and bespoke joinery push costs up.
Groundworks & Structural Work
If the site requires deep digging, reinforced foundations, steel beams or changes to support walls, expect substantial cost rises.
Professional Fees
Fees for architects, structural engineers and planning consultants typically add 10–15% onto your base cost.
Planning and Building Control
In many extensions, building regulations approval is a must — inspections, drawings, calculations and certificates all cost money.
Hidden Costs and Extras
It’s easy to under-budget if you don’t plan for:
VAT: Usually 20% on construction work (though some energy-efficient builds may qualify for relief)
Contingency: Always include at least 10%+ for surprises — hidden drainage issues, unexpected structural work or delays.
Utilities relocation: Moving gas, water or electrical services (especially if walls are knocked through).
Landscaping & finishes: New patios, decking or garden remodelling.
What Real Homeowners Are Seeing
Community feedback suggests real variances:
Some homeowners report seeing prices closer to £1,800–£3,000/m² for standard builds — but higher in London contexts.
Larger single-storey rear extensions (~27m²) can be £60k–£90k even outside the capital.
Quotes over £5,000/m² — though rare — show the importance of comparing builders and itemised pricing.
Value for Money: Is It Worth It?
A well-executed extension can significantly increase a home’s value and improve everyday living — especially if it modernises layout and creates open plan living space or additional bedrooms.
However, high costs in some regions mean returns on investment vary. Many experts advise thinking of extensions as improving your quality of life first, with capital uplift as a bonus.
Tips to Save Money Without Cutting Corners
Get multiple quotes — at least three, itemised quotes, not just lump sums.
Employ an architect early to manage design and avoid expensive changes mid-build.
Consider modular or prefabricated builds — sometimes faster with tighter cost controls.
Lock in material and labour contracts early — prices can fluctuate.
Always budget a 10–15% contingency for surprises.
There is no one-size-fits-all price for home extensions and each project is shaped by design, location, site conditions and quality expectations. However, by understanding the typical costs, planning carefully, and budgeting realistically, you can turn your extension dream into reality without financial shock.
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