How Much Does A Single Storey Extension Cost?

How Much Does A Single Storey Extension Cost?


Adding a single storey extension can be an excellent way to create more living space in your home. However, before starting an extension project, it is important to have a realistic budget in mind. There are several key factors that influence the cost of building a single storey extension.

Cost Factors

The main elements that impact the overall price tag include the size of the extension, location, specifications like foundations, roof, windows and utilities, additional services such as planning permission and project management, as well as the materials used. Being aware of these cost considerations from the outset can help homeowners plan and budget accordingly.


Not surprisingly, the size of the extension has the biggest effect on the final costs. As the square footage increases, so too do the costs for materials, labour, site works and the amount of construction required. As a rough estimate, small single storey extensions less than 30 square metres may cost around £25,000 while larger additions over 40 square metres could be £60,000 or more.


The part of the UK where you live also affects extension expenses. There are considerable regional differences in labour and material expenses across the country. Building costs in the South East and London tend to be higher while there are more affordable rates in the North, Scotland and Wales. Site constraints can also impact pricing. Difficult access, trees to work around or sloped sites all add complexity and costs.


The types of specifications you include for elements like the foundation, roof, windows and utilities provision also push the budget up or down.


For small extensions, choices range from concrete strip foundations to more affordable timber beam or steel beam designs. Complex soil conditions or slopes may require extra civil engineering works which adds substantial expense.


A simple flat roof can cost less than a complex pitched alternative. Using reclaimed tiles or more affordable manufactured alternatives is cheaper than premium new slate or clay tiles. Insulation, drainage and rooflights also impact the roof budget.

Windows & Doors

Standard double glazed aluminium or uPVC frames cost less than premium materials like timber but have a shorter lifespan. Energy efficient glazing options are more expensive but save money long-term. Bi-folding or large span doors and windows tend to increase rates over standard sizes.


Connecting drainage, electrics, heating, data cabling and possibly water lines all needs factoring in too, especially for larger more complex extensions. Underfloor heating, air conditioning, smart home systems or renewable energy sources increase costs but may add value long-term.

Additional Services

There are a few supplementary items that often get overlooked when budgeting for an extension build.

Planning Permission

In some cases, planning permission will be required which incurs fees to submit applications and documents. There may also be costs for surveys, drawings and revisions to get approval.

Architect Fees

An architect can provide valuable support with the designs, planning approval and overseeing the build. Their services typically cost 8-15% of the total project price.

Project Management

A dedicated project manager is recommended for larger extension builds to coordinate all the trades, scheduling and works. Their fees may be 10-20% of build costs.

Cost Saving Tips

To make an extension more affordable, consider DYing the strip foundations, using reclaimed materials wherever possible, installing basic fixtures and fittings from budget brands, and project managing the build yourself. Smaller touches like building shelves into alcoves instead of installing fitted units helps pare back expense too.

Estimated Costs

As a guide, here are the typical costs for single storey extensions across three common size brackets:

Small Extension

For compact extensions less than 30 square metres, expect to pay around £25,000 – £40,000. At this size, costs average out at roughly £1,200 – £1,500 per square metre.

Medium Extension

For mid range extensions of 30 to 40 square metres, budget around £40,000 – £80,000. Cost per square metre averages £1,300 – £2,000.

Large Extension

Larger extensions over 40 square metres often cost between £60,000 – £150,000 with around £1,500 – £2,500 per square metre. Higher end costs reflect extra complexity and bespoke designs.

Financing Your Extension

With sizable price tags, financing an extension build is an important consideration. Many homeowners use existing equity in their property, remortgage, or access loan products specifically tailored for home improvements. Comparing interest rates and repayment terms is wise to keep borrowing costs affordable.


Adding extra living space with a single storey extension can be achieved for a wide range of budgets. Being realistic about the size and specifications you need, getting quotes not estimates, and looking at cost saving measures can all help make an extension more affordable. Carefully weighing up the investment versus added value to your home is advisable too.


What is the cheapest way to extend?

The most cost effective option is building a small, simple flat roof extension with budget materials and taking on some of the work yourself to avoid labour costs.

What is the average cost per m2 for a single storey extension?

£1,200 – £2,500 per m2 is typical, influenced greatly by the size and specifications chosen.

How much does a 30m2 extension cost?

A 30m2 extension generally ranges from £40,000 – £80,000, with mid range specs costing around £60,000.

Can I get an extension on finance?

Yes, many lenders offer secured loans against your property value specifically for home improvements. An equity release mortgage or remortgage can also generate funds.

What saving tips can reduce my extension costs?

Opting for more basic specifications, using reclaimed materials, and taking on elements like the foundations yourself can all pare back the budget.

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