House Extension Cost Calculator
Get an instant cost estimate for a fully finished house extension in Greater Manchester, based on our current 2026 build rates. Set your options below and the figure updates as you go, then send us your plans and project details for a personalised quote.
Build Your Estimate
For a double storey, count both floors combined.
Standard £1,650/m² · Premium £2,400/m².
Your estimated project
£33,000
Based on £1,650 per m²
Fully finished build, construction only. Excludes VAT, professional fees and planning.
Share your project for a personalised quote
or email contact@renovat.co.uk
This calculator gives an indicative estimate for a fully finished build, for guidance only, and is not a quotation. Send us your plans and project details for an accurate, personalised quote, then we arrange a free site visit.
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View the project →How much does a house extension cost in Greater Manchester in 2026?
A fully finished house extension in Greater Manchester costs from £1,650 per square metre at standard specification and £2,400 per square metre at premium specification in 2026. As a guide, a 20m² single storey rear extension is around £33,000 standard or £48,000 premium, a 30m² extension is around £49,500 standard or £72,000 premium, and a 40m² extension is around £66,000 standard or £96,000 premium. These figures are for the construction of a complete, finished extension and exclude VAT, professional fees and planning application costs.
| Floor area | Standard (£1,650/m²) | Premium (£2,400/m²) |
|---|---|---|
| 20 m² | £33,000 | £48,000 |
| 30 m² | £49,500 | £72,000 |
| 40 m² | £66,000 | £96,000 |
| 50 m² | £82,500 | £120,000 |
What is included in the cost?
The rates cover a fully finished build. A standard finish at £1,650 per square metre gives you a complete extension to a good everyday specification, ready to use. A premium finish at £2,400 per square metre adds higher-end features such as bi-fold or sliding doors, underfloor heating, and better flooring, joinery and fittings. A new or relocated kitchen, an additional bathroom, and structural work to open the extension up to the existing house are added on top, which is why the calculator lets you include them.
| Specification | Cost per m² (finished) | What it includes |
|---|---|---|
| Standard | £1,650 | Complete, finished extension to a good everyday specification |
| Premium | £2,400 | Higher-end finishes, bi-fold or sliding doors, underfloor heating |
From Estimate to Exact Price
A calculator gives you a ballpark. To turn it into an accurate, fixed price, send us your plans and project details. We will review them, prepare a personalised quote broken down by trade, then arrange a free site visit to confirm everything. No obligation.
Send Your Project Details Or call 0161 706 0480 · contact@renovat.co.ukFrequently Asked Questions
How much does a single storey extension cost in 2026?
In Greater Manchester, we build fully finished extensions from around £1,650 per square metre at standard specification, rising to around £2,400 per square metre for a premium finish. As a rough guide, a 20 square metre standard extension is in the region of £33,000 for the finished build, before VAT, professional fees and any kitchen fit-out. The only way to get an accurate figure is to share your project details with us.
What is the difference between standard and premium?
A standard finish at around £1,650 per square metre gives you a complete, finished extension to a good everyday specification, ready to use. A premium finish at around £2,400 per square metre adds higher-end features such as bi-fold or sliding doors, underfloor heating, and better flooring, joinery and fittings. The right choice depends on your budget and how you want the finished space to look and feel.
How much does a 30m² extension cost?
A 30 square metre fully finished single storey extension in Greater Manchester is in the region of £49,500 at standard specification (£1,650 per square metre), or around £72,000 at premium specification (£2,400 per square metre), before VAT, fees and any kitchen or bathroom fit-out. Use the calculator above to model your exact size.
Is a double storey extension cheaper than a single storey?
Per square metre, a double storey extension is often slightly better value because the foundations and roof are shared across two floors. The total project cost is higher because you create much more floor area, but it is one of the most cost-efficient ways to add significant space. Send us your plans and we will give you an accurate comparison for your property.
Does an extension add value to my home?
In most cases yes, a well-built extension adds usable space and value, but the amount varies significantly with your area, your street, and the local ceiling price. A well-designed extension that creates an open-plan kitchen diner or an extra bedroom tends to add the most. Because the figure depends so heavily on your specific property and market, we give you a realistic view of value as part of a personalised quote rather than a blanket percentage.
Do I need planning permission for an extension?
Often not. Many single storey rear extensions fall under permitted development, typically up to 6 metres on a semi-detached house or 8 metres on a detached house, subject to height and design rules. Conservation areas, listed buildings and Article 4 directions can reduce those rights, and double storey and wraparound extensions are more likely to need full permission. We check your position and handle any application. See our planning permission service.
How much do bi-fold doors add to the cost?
Bi-fold and large sliding doors are a popular feature on rear extensions and are one of the main things that lift a project from a standard to a premium finish. The exact amount depends on size, material and glazing specification. They are included within our premium rate, which is why premium works out higher per square metre than standard.
Will I need a party wall agreement?
Possibly. If your extension involves work on or near a shared boundary wall, or excavating close to a neighbour's property, the Party Wall Act may apply and you would need a party wall agreement. This is common on terraced and semi-detached homes. We identify whether one is needed at the quote stage and guide you through the process.
Can I stay in my house during the build?
In most single storey extension projects, yes. The work is largely external until the point where the new space is opened up to the existing house, so many homeowners stay put throughout, with some disruption around the kitchen if that is being relocated. Larger double storey projects are more disruptive. We talk you through what to expect before work starts.
What does the estimate not include?
The calculator shows construction cost only for a finished build. It excludes VAT (usually 20 percent on domestic work), professional fees such as a structural engineer and any architect or designer, planning application fees where required, and a sensible contingency for older properties. We set all of this out clearly in a personalised written quote.
How do I get a personalised quote?
Use the calculator for a budget, then send us your plans and project details. We review them and prepare a fixed price broken down by trade, then arrange a free site visit to confirm everything, with no obligation. Call 0161 706 0480, email contact@renovat.co.uk, or send your details online. We cover all of Greater Manchester and handle planning and building regulations for you.