How much does a house extension cost in South Manchester in 2026?

A single-storey extension in South Manchester typically starts from around £2,000 to £2,800 per square metre plus VAT for the build, before kitchens and finishes. Here is what that figure includes, what it does not, and what moves the price.

The short answer: as a guide, a single-storey extension in South Manchester and Cheshire typically starts from around £2,000 to £2,800 per square metre plus VAT for the build, before kitchens and finishes. Loft conversions typically cost around £25,000 to £35,000 plus VAT for a rooflight conversion and £40,000 to £60,000 plus VAT for a dormer. Those figures are a starting point, not a quote, and the rest of this guide explains why.

I am a Chartered Civil Engineer as well as a builder, so I tend to look at cost the way an engineer looks at a structure: what is carrying the load, and where are the risks. In an extension budget, most of the risk sits in a handful of predictable places. If you know where they are, you can ask better questions and compare quotes properly.

What does the per square metre figure include?

When we talk about a build cost per square metre, we mean the structure and the shell made ready for finishing. That normally covers the groundworks and foundations, drainage alterations, walls, the roof, structural steel, windows and external doors, and the internal work to a plastered, ready-to-decorate standard.

It does not normally include the kitchen itself, flooring, decoration, sanitaryware or specialist lighting. It also excludes professional fees such as drawings, planning and building control, and any party wall surveyor. Always ask a builder exactly where their figure stops, because two quotes that look far apart are often simply measuring different things.

A worked example

Take a 20 square metre single-storey rear extension. At £2,000 to £2,800 per square metre, the build element would be in the region of £40,000 to £56,000 plus VAT. The kitchen, flooring, finishes and fees come on top, and the final figure depends on the factors below. This is an illustration of how the guide range works, not a price for your project.

What pushes the cost of an extension up?

In our experience the same few items account for most of the difference between a straightforward extension and an expensive one.

• Large openings. Wide sliding or bi-fold doors and removing the rear wall of the house mean bigger steel beams, stronger supports and sometimes a steel frame.
• Foundations. Clay soils near trees, soft or made-up ground, and sloping gardens can all mean deeper or specially designed foundations.
• Drains. A public sewer or shared drain under the footprint may need a build-over agreement with the water company, or diverting.
• Roof design. A simple flat roof costs less than a pitched roof, roof lanterns or large areas of glazing.
• Access. Terraced houses with no side access mean materials and spoil go through the house, which takes time.
• Specification. Glazing systems, flooring, heating and finishes vary enormously in price.

How much does a double-storey extension cost?

A double-storey extension usually gives more floor area for the money than a single-storey one, because the foundations and roof are built once and serve two floors. However, the structure is more demanding and planning permission is usually required. Because the variation between projects is so wide, we give you a realistic range at the feasibility stage rather than a single published figure.

What other costs should I budget for?

A realistic budget covers more than the builder's price. Before work starts you are likely to need measured survey and design drawings, structural calculations, a planning application or lawful development certificate, and building control fees. If you share a wall or boundary with a neighbour, you may need party wall notices and possibly surveyors.

During the build, the kitchen, flooring, lighting and decoration are the big items. We also recommend a contingency for the unknowns you only find when the ground is opened or the old wall comes down. Finally, check whether each quote includes VAT, so you are comparing like with like.

How can I keep an extension on budget?

The single most effective step is to get the structure and the ground understood before anyone draws the final scheme. Most budget overruns come from assumptions that turned out to be wrong: the drain was in the way, the ground was poor, the opening needed a bigger beam. When the engineer and the builder are the same person, those questions get answered at the start.

1. Get an itemised quotation, not a single lump sum with vague allowances.
2. Agree what happens if you change your mind, and how changes are priced, before work starts.
3. Choose your kitchen and main finishes early so they can be priced properly.
4. Keep a contingency and do not spend it on upgrades until the groundworks are complete.
5. Ask for a written programme with staged payments against milestones.

How long does an extension take?

A typical single-storey extension takes around 10 to 16 weeks on site, and a loft conversion around 6 to 12 weeks. Before that, allow time for design, any planning application and building regulations approval. We agree a written programme with every client before we start.

Why we give you a range before drawings

Many homeowners pay for full drawings, get planning, and only then discover the project costs far more than they can afford. We think that is the wrong way round. Our free cost guide starts with a call, then a site visit where the project is a good fit, and gives you an honest view of what is structurally possible and a realistic budget range before you commit to design fees.