House Extension Costs

House Extension Cost: 2022 Price Comparison UK

Asking how much does a house extension cost? Is a little bit like asking the proverbial ‘how long is a piece of string? There is no one simple answer because the question fails to address the variables involved. For example, you can use an extension cost calculator to give you a rough estimate, but without an understanding of the extension rules, regulations, and costs, you are likely to miss out various elements of the equation, leaving you with an inaccurate and unrealistic calculation.

To know how much your house extension would cost, you need to be clear on what those variables are and how they relate to you specifically. Broadly speaking, these variables can be boiled down to the following:

  • The type of the extension
  • The size of the extension
  • The type of the property
  • The location of the property – especially if it’s in London!
  • The contractors you use (unless you DIY, which could end up costing more if you aren’t a professional)

Other concerns include:

  • Planning permission, including trees and other nature concerns
  • Fire regulations
  • Insurance
  • Estimates and substitutions
  • VAT
  • Fixtures & fittings, including windows
  • Finishing touches

Different kinds of Extension

The type of extension you are considering will greatly affect the overall cost.

The cheapest kinds of extensions are the addition of a conservatory, at around £5,000 upwards, depending on the size and the materials used. Other cost-effective options are loft or garage conversions, which often work out cheaper than building an extension. However, these options may not apply to you, depending on the size, age, location, and design of your property.

Single Storey Extension

Single-storey extensions can vary greatly in price depending on where you live, and the quality of the materials and design, but UK guide prices in 2020 are as follows:

  • Small Extension – £16K to £21K
  • Medium Extension – £26K to £34K
  • Large Extension – £52K to £67K

These prices do not include VAT (an extra 20% of the fee) or design/architecture costs which can add another £500 – £1,000 onto your total. Planning permission can cost up to £200 to obtain from your local authority, although it is not always needed for an extension, whilst building regulations can cost you up to £500 in some cases.

However, as the top-end estimate of the small extension is close to the lower price for a medium-sized extension and so on, experts advise you to pay for the largest size you can afford, rather than paying more for a small but fancier extension. After all, it is the space which will add value to your home.

Two-Storey Extension

Two-storey extensions cost around 1.75 times the cost of single-storey extensions for the materials, but you also need factor in labour costs being almost doubled.

You may also incur other costs, such as the need to build the same kind of roof as that of the main house – more info about new roof costs. There is also the question of whether the foundations are suitable to support the additional weight.

Kitchen or Bathroom

With a kitchen or bathroom extension, you need to factor in plumbing and electricity costs, around £5,000 upwards for a bathroom and £10,000 for a kitchen, but these are basic figures that don’t take into account the vast difference in prices for different designs, layouts, and finishes. You will also need to make sure the work complies with the UK Water Regulations.

Bungalow Extension

Bungalows are single-storey properties, so extending outwards or upwards usually costs similar to a single-storey extension, however, bungalows sometimes have interior walls which are not structural and can take some of the labour costs away from a usual single-storey extension. As with a two-storey extension, you will need to match the original roof. On the flip side, many bungalows cannot support another storey, as they don’t have the foundations to do so, so extending outwards could be your only option.

Location, Location, Location

Where you live vastly impacts the price you will pay for an extension. Those living in London or the South East can expect to pay at least £20,000 extra. It can also affect the ceiling price of your home, so be sure to check with a local estate agent to make sure your property isn’t already at its ceiling price before you consider an extension.


We’ve all heard the saying you can only pick two from ‘good/fast/cheap’ and it applies, to a degree, in building an extension. However, it is possible to find a balance, and the more prepared you are, the better chance you have of sticking within your budget.

As with all aspects of house building, buying, or development, research is key – you should shop around for quotes and compare service reviews from at least three reputable firms before choosing your builders. You should also be working with a qualified architect, particularly for more ambitious extensions.

Once you have your quotes, don’t forget to take VAT into account (around 20%) of the fee, and then try to leave some wiggle room in your budget for unforeseen circumstances or necessary substitutions.

Finally, make sure you’ve accounted for fixtures, fittings, and finishing touches in your budget. Chances are you will need windows and doors in your extension, and these items can prove much more costly than you might anticipate, particularly if they need to be anything other than the standard size. You also don’t want to get to the end of your extension and find you can’t use it because you left nothing in the budget for furnishings.

Other Concerns

You must make sure you have planning permission from your local authority before you extend either upwards or outwards. That includes getting permission to cut down trees, as many are protected by Tree Preservation Orders and could see you landed with a hefty fine if you do not obtain the proper permission.  You may also need a Party Wall Agreement with your neighbour, which can cost up to £1,000, plus the surveyor’s hourly rates of £150-£200.

Also, make sure any new building work meets fire and safety regulations, and update your insurance to reflect the new size of the property.

All in all, an extension can be a cost-effective way to add living space to your home (as opposed to moving home) but a good-quality extension will still cost you a significant amount of money, not to mention the disruption to your daily life. Therefore, you should never undertake an extension lightly, and should always be as clued-up as possible about the costs and regulations involved.

To help you out, we’ve answered a couple of frequently asked questions, below.

Frequently Asked Questions

Is it Cheaper to Extend or Build Up?

On average, it is cheaper to build outwards than build upwards (an estimated 30%). This is because more structural work is usually required to extend upwards, for a start you’ll need to remove the roof to build upwards. Then there’s the scaffolding and the extra strengthening that may be needed to accommodate the extra work. That’s if the property is suitable for adding another floor, as many aren’t.

For example, bungalows are usually designed to support only one storey, so adding another could be met with all kinds of issues. However, bungalows often have non-structural inside walls which can help you to extend outwards.

Extending outwards could be a low-cost option if it is the form of a conservatory or a simple timber-framed extension, on which you will save money in reduced labour time.

Of course, depending on your property, and its location, you may not have the option of extending outwards. You may not be able to get planning permission for cutting down trees, you may simply not have the required space, or you might not have land suitable for building on (such as a steep slope) which would add extra costs to an extension, even if it was a viable option.

Still, there are significant benefits to adding a double-storey extension, which could add an estimated 30% to 60% to the value of your home, particularly if it is in the form of a double bedroom and en-suite bathroom. 

Does an Extension Always Add Value?

In most cases, adding living space to your house in the form of an extension will increase its value. However, there are a few circumstances where this is not the case. If your house is already priced at the top end of the market for your street or area, an extension will not mean buyers will pay more, so you haven’t added any value and are unlikely to recoup the costs of the extension even if you do manage to sell. You should, therefore, check with a qualified estate agent what the house’s ‘ceiling price’ is before you go ahead with an extension.

 You also need to take in to account other costs such as extra work being required due to the size/location of the property – for example, sloping ground will require foundations to be laid.

There’s also a question of taste and quality. A conservatory is a very popular extension, but using cheap or unattractive materials can actually detract from the overall value of your property. Common sense and convenience are also factors, for example, an addition bedroom with no en-suite and restricted access to the main bathroom make it less than buyer-friendly.

If you are planning to sell the property in the near future, securing the planning permission for an extension for the next occupants could make the property more desirable to potential buyers, without you having to actually pay for the extension, not to mention undergo the disruption such work inevitably causes.

Is it Better to Extend or Move?

Both have their advantages and disadvantages, so it all depends on what is going to benefit you the most. If you need more living space because your family is expanding, for example, you need to weigh up the cost and disruption of an extension versus the cost and disruption of moving house. You also need to consider whether the house and the area you live in meet all your other needs. If the only issue with the house is that you have run out of useable living space then an extension could be the answer. On the other hand, if you don’t see yourself living in the property long-term then it may be time to move.

Budget also factors in. You may be able to raise the cash needed for an extension easier than you can fund a move to a bigger house. However, in both cases, you need to understand all the costs involved in each course of action. An extension will (usually) add value to your home, as well as space, but if the property or area is not meeting your needs in other ways – such as school districts, commuting time, or the lack of a garden, for example, extending the property may not add as much value to your life as moving to a better-suited property or area would.

What is the Cheapest Way to Build an Extension?

The cheapest way to build an extension is to build it yourself, however, this is only true if you have the required skills to do so.  Never ever attempt plumbing, electrical work, or major structural work unless you are fully qualified to do so. Attempting DIY above your skill level can be both dangerous, and end up costing you more when you have to pay professionals to fix your mistakes. You should always work with qualified builders, plumbers & electricians (if necessary) architects, and estate agents when planning an extension. 

However, if you have done your research properly and have the time, you can be your own project manager – saving 15 to 20 per cent of a builder’s fee.

Securing all the appropriate planning permissions and brushing up on building and fire regulations is also essential in saving you money. You can be heavily fined for cutting down a tree without permission, and you may need to spend more money to get your extension to comply with building and fire regulations after the fact if you have cut corners during the build.

Keeping the design simple is one way to build an extension on a budget – a square extension with a simple pitched roof is much cheaper than adding angles, curves, or other custom design features.

Your choice of materials will also significantly affect the cost of your extension. Stick off the shelf rather than anything you have to order specially. If you have the expertise to do so, using reclaimed materials can also save you a lot of money.

Make sure your initial budget includes post-build costs such as fixtures, fittings, and furniture, which will encourage you to stay within it on the initial build. Also, prioritise and budget accordingly, for example, if you really need a specific expensive custom-made sink, you may have to sacrifice your first-choice flooring for a cheaper option.

Is it Cheaper to do a Loft Conversion or an Extension?

The short answer is that a loft conversion is cheaper than an extension. An average single-storey house extension is estimated to cost between £1,500 to £1,900 per square metre, whilst you are looking at between £1,150 to £1,350 per square metre, for a simple loft conversion.

Converting the loft into an extra double bedroom and en-suite bathroom could add an average of 21 per cent to the value of a property, and 24.5 per cent in London. However, a different kind of extension (such as a conservatory) may add value to the property for around £5,000 upwards, potentially giving you a greater return on your investment in the future.

The age and style of the property is also a factor, as converting a loft in a period property could have hidden expenses such as needing a full rewiring, or a new roof. On the other hand, extensions may also have hidden cost such as need foundations lying on sloping ground, and create greater disruption to your life. One of the reasons loft conversions are so popular is that, on the whole, they are less disruptive than an extension. It really depends on your reasons for converting/extending, and which option is most suited to your lifestyle.