Home extension: how much does it cost?

Home extension: how much does it cost?

Last updated: 21/01/2022

Extending your property is a great way to gain more liveable space, without the hassle of moving home. 

Extensions don’t come cheap, but as well as providing some crucial extra space, they can add to the value of your house.

Read on to find out how much you can expect to pay on average.

What type of extension do I want?

First of all, you’ll need to think about the type of extension you want to invest in. Do you want a fairly standard, box-shaped single-storey extension? Or maybe you plan to go all-out on a double-storey extension with good-quality materials?

Bear in mind that the prices given below are averages. There are many variables, such as where you live in the UK or whether you’ll need your extension plumbed in, all which will impact on the costs.

Single-storey extension cost
Basic quality £1,350 – £1,650/m²
Good quality £1,700 – £2,000/m²
Top quality £1,800 – £2,500/m² and above

Source: https://www.homebuilding.co.uk/advice/how-much-does-an-extension-cost

So what would be the total average cost for an extension of 30m²? According to tradesperson-finding website Household Quotes, the build cost would be between £30,000 and £48,000. This should take about eight to 10 weeks to complete.

single-storey extension

Image from Your Job Cost

Double-storey extension cost

If you’re looking to extend two storeys, you’d be looking to pay the following:

Basic quality £1,250 – £1,650/m²
Good quality £1,650 – £2,250/m²
Top quality £2,250 – £3,000/m² and above

Source: https://www.homebuilding.co.uk/advice/how-much-does-an-extension-cost

According to Household Quotes, a 40m² two-storey extension is likely to cost between £48,000 and £76,000 if you’re working on a budget. You should expect the work to take about 12 to 16 weeks.

double-storey extension

Image from My Home Extension

Side extension cost

Side extensions can be a clever way of creating more space inside, while not encroaching too much into the garden.

According to home improvement website Homebuilding & Renovating, a basic side extension should cost roughly £1,500 – £2,000 per m². Homeowners should budget from £75,000 and up, although prices will vary depending on factors such as quality of materials, and how much reconfiguration needs to be done. For example, if you plan to put a kitchen in the extension, this will need to be plumbed, and you’ll need pipes reworked if you have a gas cooker.

A side extension should take roughly 10 to 12 weeks to complete.

side extension

Image from My Job Quote

Flat-pack extension

As the name suggests, this is the quick and dirty option – although it’s not necessarily cheap, especially if you are looking for a top quality finish. According to Household Quotes, average prices for a flat-pack extension are as follows:

Basic quality £750 - £1,140/m²
Good quality £1,275 - £1,800/m²
Top quality £1,650 – £3,600/m²

Source: https://householdquotes.co.uk/cost-of-extension/

These can take just one to two weeks to install. You need to choose a style sympathetic to your home though, otherwise you risk it losing value overall.

side extension

Image from Timber Rooms

Loft conversion cost

Another popular way to extend your living space is by converting your loft. Again, costs will vary depending on what exactly you’d like to achieve. According to tradesperson quote site MyJobQuote, you can expect to pay the following average costs for a loft conversion:

Roof-light conversion £15,000 – £20,000
Dormer conversion £30,000 – £60,000
Hip-to-gable conversion £40,000 – £65,000
Mansard conversion £45,000 – £70,000

Source: https://www.myjobquote.co.uk/costs/loft-conversion

If you’re thinking about converting your attic, but don’t know where to start, read the beginner’s guide to loft conversions here.

Other things to budget for

Most of the costs here are for the materials and installation of the structure, but don’t account for fixtures and fittings.

There are some other things to consider, which you’ll have to budget for:

  • Using a building contractor or architect will cost extra. Architect design fees can set you back up to 10% of the construction cost.
  • Any drawings and designs you have made will cost extra.
  • If you need a structural engineer, you’ll have to pay for their visit. This will cost on average £400 for simple domestic projects.
  • Hire a registered electrician to do the rewiring. They tend to charge around £40 an hour, or a day rate of £200 to £250.
  • If you need a plumber, they usually charge between £40 and £80 per hour. And if you need gas work done, be sure to hire an engineer on the Gas Safe Register. This should cost about £75 an hour.
  • Consumer magazine Which? recommends that you should set aside an extra 10% for unexpected additional costs.

Also, bear in mind that builders are likely to request payment in stages, so allow for this when managing your cashflow.

How can I cut the cost of building an extension?

The fewer people you have to pay, the cheaper building an extension is likely to be. While it’s good to leave the whole job to the pros if you can afford it, there are a few things you can take into your own hands.

Read our guide: Home extension: DIY or call in the builders?

Generally speaking, for all work you want to carry out on your home, you should compare quotes from at least three different tradespeople. Also, to make sure you’re budgeting correctly, always check that VAT is included.

Click on the buttons below to read more content about home improvements:

DIY on a budget: money-saving tips
Loft extension: How do I start?
DIY or call in the builders?

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