Extension Builders
House and Home Extensions
An extension is one of the biggest investments you will make in your home. Done well, it changes how you live in it. Done badly, it creates problems that are expensive to put right.
We design and build house extensions with our own directly employed team. Design, planning, structural work, groundworks, brickwork, roofing, plumbing and electrics are all handled in-house and run as one project, under one fixed-price contract.
Most homeowners come to us at one of two stages: with a clear brief that needs delivering properly, or knowing they need more space but unsure what their plot allows. We work with both.
Looking for a local team? See our pages on house extensions in Milton Keynes and house extensions in Buckingham.
How It Works
How an Extension Project Works
STEP ONE
Site Visit and Brief
We measure up, talk through what you need and your budget, and check your home’s planning history and permitted development position before any design work begins.
STEP TWO
Design, Planning and Quote
Our design and build team produces planning and Building Regulations drawings, submits any application, and gives you one itemised fixed price before work starts.
STEP THREE
The Build
Our own site team carries out the work. Single-storey extensions take 10 to 16 weeks on site, double-storey 16 to 24 weeks. We host every building control inspection.
STEP FOUR
Handover
Snagging is completed and the building control completion certificate issued before the project closes. Most projects run 6 to 12 months from first conversation to completion.
What We Build
Types of Extension We Build
Rear Extensions
The most common extension and the simplest in planning terms. Adds ground-floor space to the kitchen or living area, and often falls within permitted development.
Side Return Extensions
Infills the narrow passage beside the kitchen on Victorian and Edwardian homes. A steel beam bridges the span, and a cramped kitchen becomes a usable room.
Wraparound Extensions
Combines a rear and side return extension for the largest possible ground floor. Almost always needs planning permission and more structural work.
Single-Storey Extensions
Space where you need it without building above. Roof design, natural light and how the new space connects to the existing house are the key decisions.
Double-Storey Extensions
Bedrooms and living space in one build, at a lower cost per square metre because foundations, walls and roof serve both floors. Planning permission is almost always needed.
Kitchen-Diner Extensions
The most requested project: a single-storey rear addition with bifold doors, rooflights and underfloor heating, opening the kitchen into the garden.
Pricing and Budgets
How Much Does an Extension Cost?
A single-storey extension typically costs £1,800 to £2,800 per square metre to build, depending on specification. Double-storey extensions cost less per square metre because foundations, walls and roof serve both floors.
Professional fees, VAT and any structural work to the existing house sit outside the build cost. Every quote follows a site visit.
We provide fixed-price quotes. What we quote is what you pay, unless you change the scope.
Single-storey extension
£1,800 to £2,800 per m²
Build cost per square metre at a standard specification, before fees and VAT.
Example: 20 m² rear extension
£36,000 to £56,000
Roughly 4 by 5 metres, a typical kitchen-diner extension.
Double-storey extension
Lower per m²
Foundations, walls and roof shared across two floors. Priced after survey.
| Scope | What’s typically involved | Indicative range |
|---|---|---|
| Single-storey extension | Build cost per square metre at a standard specification, before fees and VAT | £1,800 to £2,800 per m² |
| Example: 20 m² rear extension | Roughly 4 by 5 metres, a typical kitchen-diner extension | £36,000 to £56,000 |
| Double-storey extension | Foundations, walls and roof shared across two floors | Lower per m², priced after survey |
Pricing and Budgets
How Much Does an Extension Cost?
A single-storey extension typically costs £1,800 to £2,800 per square metre to build, depending on specification. Double-storey extensions cost less per square metre because foundations, walls and roof serve both floors.
Professional fees, VAT and any structural work to the existing house sit outside the build cost. Every quote follows a site visit.
Single-storey extension
£1,800 to £2,800 per m²
Build cost per square metre at a standard specification, before fees and VAT.
Example: 20 m² rear extension
£36,000 to £56,000
Roughly 4 by 5 metres, a typical kitchen-diner extension.
Double-storey extension
Lower per m²
Foundations, walls and roof shared across two floors. Priced after survey.
| Scope | What’s typically involved | Indicative range |
|---|---|---|
| Single-storey extension | Build cost per square metre at a standard specification, before fees and VAT | £1,800 to £2,800 per m² |
| Example: 20 m² rear extension | Roughly 4 by 5 metres, a typical kitchen-diner extension | £36,000 to £56,000 |
| Double-storey extension | Foundations, walls and roof shared across two floors | Lower per m², priced after survey |
Planning Permission
Do You Need Planning Permission?
Not always. Many single-storey rear extensions fall within permitted development. We check your position at the first visit and recommend a lawful development certificate where it applies.
- Permitted development limits. Up to 4 metres deep on a detached house or 3 metres on others, rising to 8 and 6 metres under the larger home extension scheme with neighbour consultation.
- When it does not apply. Conservation areas, areas of outstanding natural beauty, listed buildings, and estates where rights were removed by a planning condition.
- Full applications. Typically 8 to 12 weeks from submission to decision. We manage the application and liaise with the planning officer on your behalf.
Experienced Extension Specialists
Why Choose Us for Your Extension
We are Federation of Master Builders members who have completed dozens of extensions. The people who quote your project are the people who build it.
- Every trade in-house: no subcontractors you have never met
- Fixed-price quotes based on measured quantities, no surprise costs
- Planning applications, structural input and building control handled by us
- Experienced team on site every day until completion
- Quality checks at every stage before work moves forward
- Federation of Master Builders approved, backed by our 10 Point Guarantee
Common Questions
Extension FAQs
Service Areas
Where We Build Extensions
From our base in MK18 we build extensions across the surrounding towns and villages. Read more about house extensions in Milton Keynes and house extensions in Buckingham.
- Milton Keynes
- Buckingham
- Newport Pagnell
- Olney
- Woburn Sands
- Bletchley
- Winslow
- Brackley
- Towcester
- Bicester
Service Areas
Where We Build Extensions
From our base in MK18 we build extensions across the surrounding towns and villages. Read more about house extensions in Milton Keynes and house extensions in Buckingham.
- Milton Keynes
- Buckingham
- Newport Pagnell
- Olney
- Woburn Sands
- Bletchley
- Winslow
- Brackley
- Towcester
- Bicester
Meet the Senior Leadership Team
Get In Touch
Get a Quote for Your Extension
Tell us what you’d like to build and we’ll arrange a visit to talk through what your home allows, the likely cost and a realistic timescale.
