How Much Does a House Extension Cost in Milton Keynes? (2026 Full Guide)
- Clarkson Construction
- Nov 22
- 6 min read
If you’ve been thinking about extending your home in Milton Keynes, you’re in good company. With families growing, remote work becoming the norm, and house prices rising across Buckinghamshire, many homeowners are choosing to upgrade the home they already love rather than deal with the stress (and cost) of moving.
But the same question always comes up first:
“What does a house extension actually cost in 2026?”
If you’ve Googled it, you’ve probably found vague answers or national estimates that don’t reflect Milton Keynes’ real prices. That’s why we’ve put together this honest, local, and up-to-date guide - based on real construction work across Milton Keynes, Buckinghamshire, Northamptonshire and Bedfordshire.
Whether you’re dreaming of a bigger kitchen, an open-plan living space, a home office or extra bedrooms, this guide will help you understand what’s possible, what it costs, and how to get the best value from your build.
So, what’s the average cost of a house extension in Milton Keynes in 2026?
For most homes in Milton Keynes, here’s what you can realistically expect:
Single-storey extensions: £1,800–£2,400 per m²
Double-storey extensions: £2,200–£3,000 per m²
Rear kitchen/diner extension: £35,000–£75,000+
Loft conversions: £30,000–£55,000
Garage conversions: £12,000–£25,000
These figures are broad because - just like houses - no two extensions are exactly the same. The size, access, ground conditions, roof choice, structural work and interior finish all play a part. Let’s break down the common extension types to help you understand where your project might fall.
Types of Extensions and Their Real Costs
1. Single-Storey Rear Extensions
A rear extension is the most popular project in Milton Keynes right now - especially in areas like Brooklands, Broughton, Shenley, Walnut Tree, and Newport Pagnell and Olney. They’re perfect if you’re craving a bigger, brighter family space or want to transform your kitchen into the heart of the home.
Typical cost: £30,000–£70,000
The price depends on:
How far you extend
Whether you want a flat or pitched roof
Choice of glazing - Bi-fold/sliding doors
Kitchen installation and specification
Structural steels required
Homeowners love this option because the transformation is huge - and it adds fantastic resale value. These extensions offer one of the strongest returns on investment and dramatically improve everyday living.
2. Double-Storey Extensions
If you want both more downstairs space and an extra bedroom or bathroom upstairs, a double-storey extension gives you the best value per square metre.
Because the foundations and roof are shared, the cost per m² works out better than a single-storey. It all depends on width, roof design and structural requirements.
Typical cost: £55,000–£120,000+
This option is great for:
Growing families
Homes needing an extra bedroom
Increasing property value for future resale
3. Side Extensions
Many Milton Keynes homes have unused side space that’s perfect for a slim but effective extension. Side extensions are common in areas like Newport Pagnell, Walnut Tree and Shenley. They’re ideal for utility rooms, small kitchen expansions or boot rooms.
Typical cost: £25,000–£55,000
Side extensions are ideal for:
Utility rooms
Boot rooms
Small kitchen expansions
Downstairs bathrooms
They’re less intrusive but still make a big difference to daily life.
4. Loft Conversions
Loft conversions are booming across MK areas like Downs Barn, Great Linford, and older villages like Woburn Sands and Hanslope. They create fantastic bedroom, office or ensuite spaces without extending outward.
Typical cost: £30,000–£55,000
They’re one of the quickest ways to add:
A new master bedroom
An office
A playroom
Ensuite bathrooms
& more...
No need to touch your garden footprint - meaning no loss of outdoor space.
5. Garage Conversions
Often the most cost-effective extension type for homeowners wanting more functional space with minimal disruption - garage conversions are often a smart choice.
Typical cost: £12,000–£25,000
A simple, smart way to turn unused space into:
A gym
Office
Bedroom
Utility room
Playroom
And because the structure already exists, build time is short and costs stay low.
What Actually Affects The Cost of Your House Extension?
No two extensions are the same, but the main cost drivers stay consistent. Here’s what builders look at when pricing your project:
The Size and Footprint
Bigger extensions cost more - but the price per m² usually goes down as size increases.
Groundworks and Foundations
Milton Keynes sits on notoriously clay-heavy soil. Sometimes this requires deeper foundations or extra structural reinforcement.This can add a few thousand to the total cost but is essential for long-term stability.
Structural Changes
Removing load-bearing walls? Adding steels? Creating open-plan living? Removing load-bearing walls or going open-plan requires RSJ steels and professional engineering - increasing both quality and cost.
Structural work is one of the biggest cost variables - but also one of the most valuable.
Roof Complexity
Flat roofs are cheaper and faster and more budget friendly.
Pitched roofs look premium and last longer.
Roof lanterns or skylights add wow-factor (and cost).
Glazing Choices
Bi-folds, sliding doors, panoramic windows and roof lanterns can completely change the feel of your extension - and the budget.
Kitchen and Interior Spec
A basic kitchen might be £4,000. A premium German kitchen could be £20,000+.
Flooring, lighting and finishes also make a big difference.
Access To The Site & Logistics
Terraced homes or tricky driveways can affect labour time and skip access.
Do You Need Planning Permission in Milton Keynes?
Many Milton Keynes homes can be extended under Permitted Development, which means you don’t always need full planning permission.
You will likely need:
Building Regulations approval
Possible Party Wall Agreement
However, planning is required if:
You live in a conservation area
You’re extending more than 3–6 metres from the rear
It’s a double-storey extension
You’re increasing the height of the building
All extensions must comply with Building Regulations, so structural safety and insulation standards still apply.
If you’re unsure, we handle this for you under our project management service - including liaising with MK Council.
How Long Does A House Extension Take?
Although build times vary, most extensions fall into:
Single-storey: 8–12 weeks
Double-storey: 12–20 weeks
Loft conversion: 4–8 weeks
Garage conversion: 2–4 weeks
At Clarkson Construction, we provide a clear schedule before work begins - no guesswork, no surprises.
Will An Extension Add Value to Our Home?
Absolutely - extensions are one of the strongest value-boosting home improvements available and Milton Keynes is one of the best places to invest in extra space.
A well-built extension can add:
10–20% to your home’s value
More saleability
Larger living space
Modern open-plan layouts
Energy-efficient upgrades
Typical value increases:
Kitchen/diner extension: +10–15%
Double-storey extension: +15–20%
Loft conversion: +10–20%
Garage conversion: +8–15%
And buyers in Milton Keynes LOVE extended homes because they’re family-friendly, offer more space, better layouts, modern living and they're move-in ready.
How To Keep Your Extension On Budget (Builder-Approved Tips)
Over the years, we’ve seen what drives costs up - and what keeps them down.
Here’s what will save you money:
Plan your layout early
Change-of-mind mid-build = extra cost.
Keep plumbing in roughly the same place
Moving soil stacks, boilers or drainage increases costs significantly.
Choose standard glazing sizes
Custom-made glass can be £££.
Avoid lowest quotes
Cheap quotes are cheap for a reason - they’ll cost you later.
Work with a builder who manages everything
Structural work, roofers, electricians, plumbers, project management - When it’s all in-house, costs stay predictable.
Thinking About Extending Your Home? Get an accurate, honest quote for your house extension
If you’re extending your home in Milton Keynes, Buckinghamshire, Northamptonshire or Bedfordshire, Oxfordshire or the surrounding areas, Clarkson Construction can give you a no-pressure, no-obligation quote based on your plans.
We’re known for:
High-quality craftsmanship
Local reputation
Clear communication
Reliable timelines
Family-run values
What is the cheapest type of house extension?
Garage conversions are usually the most budget-friendly option, starting from £12,000.
Do I need planning permission for a single-storey extension?
Many single-storey extensions fall under Permitted Development, but size and location determine eligibility.
How long does an extension take to build?
Most extensions take 8–20 weeks depending on size and complexity.
