How Much Does a House Extension Cost?

House Extension Cost Summary
Price Range = £22,916 to £76,000
Average Cost = £45,333
Cheapest Price = £22,916

Related Guides: Garage Conversion Costs, Basement Conversion Costs
Home Extension

If you want more room in your home but don’t really want to move why not extend your house and stay in your favourite suburb? You can add more room, another bathroom, bring in more light and have a bigger kitchen, all of which will add value to your home.

The home extension cost may seem beyond you but with careful budgeting once you have a rough idea of the amount and you will soon have that extra room you need for your growing family. It is a big step adding an extension to your home and careful planning and designing needs to be carried out first. The house extension price will also include any planning fees and not just the price of the building materials.

You need to know about the building regulations you need to comply with as well as thinking about location of sewers and other infrastructure. Getting a professional builder in and talking about what you need is a good place to start. The builder can offer you house extension ideas that you may not have thought of or even considered as a possible option.

House Extensions Costs – things to Consider


Once you have a plan for your home extension, as well as the price for materials for the structure there are all of the finishing touches needed. It is important to remember that your house extension cost includes not just the building but the interior finishing as well.

Actual house extension prices

This will include costs associated with digging and excavation, concrete foundations, new roofing and tiling, guttering, down pipes, windows, doors, internal and external plastering and rendering, plumbing and electrical costs as well as heating costs.

Alterations to the main house

The builder will need to gain access to the extension by removing an existing external wall. This could involve steel support beams, flooring and general disruption to the household while this is done. Many builders leave this job as late as possible so there is the least amount of disruption.

Administrative and miscellaneous costs

This can include hiring skips for rubbish removal, a project manager, architect fee, insurance and any building control and search fees. If you are changing your mortgage or getting a new one for the extension there are also bank fees to consider.

Interior decoration and refurbishment

These costs include all of the decorator items, such as light fittings, switches and paint, wallpaper and floor coverings to match the rest of your home.

A few other considerations

Will you be extending out or up? To extend up a builder needs to make sure that the existing house structure will hold the extra weight of another storey. If it won’t you may have to reconsider extending out onto your block of land.

You may need to get planning permission before you even think about what you would like to build. If your home is in a heritage area you will only be able to do certain extensions that need to be sympathetic to the original structure.

Costs for different Types of Extensions

Pre-fabricated extensions

A pre-fabricated or flat pack extension will be between 10 and 25% cheaper than an extension built on site. Your extension is built primarily in a factory where the walls are constructed and then put together on site. This is a popular choice for owner builders as there is a lot less work involved.

Glass extensions

These are conservatories and can let a lot of light into your home and give you a lovely place to grow orchids and other plants that you would otherwise be unable to grow. The glass is a special quality and is often double glazed for added insulation. The roof can even be made of glass for even more light. A totally glass room or box can be yours from £24,000 through

Timber frame extensions

These are the extensions built on site from sustainable timber and are an eco-choice for the home owner. These can be built to match the existing home, well insulated and made to look like part of the original home and not an extension.

How much does a home extension cost?

The cost of extension will depend on the size and the materials it is made of as well as the interior finishes.

Glass room extensions

These prices are from Samson Awnings current at March 2013

  • Weinor Glass Room – 3m width x 3.5m projection, sliding frameless glass doors on all three sides, from  £17-£18,000 fitted inclusive of VAT

  • Weinor Glass Room – 6.5m width x 4m projection with sliding frameless glass doors on all three sides, from £28,000 fitted inclusive of VAT

  • Weinor Terrazza glass terrace cover with under glass awning with lights and heater :  5m width x 4m projection from £14,150 fitted inclusive of VAT

Timber extensions

  • A rough idea for the price of a timber extension is to work on around £1200 per square metre according to Evis Build for a 60 square metre rear extension.

  • For a double storey extension, you are looking at about 160% of the cost for a single storey extension of the same floor area. For example a single storey 25 square metre extension may cost £33,000, a two storey extension will be around £53,000

There are so many home extension ideas to choose from that there is one to suit any budget.

Examples of House Extension Costs

So just how much do house extensions cost? Of course, there is no real way of knowing until you’ve got an exact idea of what you want and gone through it was a professional assessor, quantity surveyor and accountant; that said, we’ve managed to source the following estimates to help give you a notion of just how much needs to be put by before you can begin:

  • According to a ServiceMagic customer survey of home renovation costs, the average cost of a home extension is £25,000

  • A Double Storey Extension costs between  £45,415 and £76,000 says WhatPrice

  • A Single Storey Extension costs between  £22,916 and £37,000 says WhatPrice

  • Planning and Preparation for a home extensions costs between £5,132 to £10,150 says Whatprice

For more accurate figures you should start getting in touch with a professional home extension company as soon as possible. They will be able to go over your ideas and provide and an up-to-date assessment of your property in a way that should help streamline your plans and keep the cost of your home extension as low as possible! Be wary of cheap house extensions, as they may not be of the best quality and may not meet UK regulations. Remember, if the price seems too good to be true, it probably is.

*Sources: ServiceMagic Home Renovation Cost Survey,, Vision Development. Figure are accurate as of November 2012.

Sarah Rammala says:


I am planning to build an extension of kitchen, bathroom and 1 bedroom on the ground floor.

mjackson says:

Hi Sarah,

Thanks for your post.

Please feel free to fill in our online request form and we will aim to match you with up to 4 local contractors who will call you in order to arrange a convenient time for them to visit you and provide you with a free quote.

We also have a cost guide should you wish to get an idea of price without having to speak to a contractor.

We hope this helps.

Mel says:

Hi I’m looking at buying a bungalow but need to extend on the side. Either a lounge and kitchen extension or 2 bedrooms and bathroom. Before I put an offer on the bungalow I could do with an idea of price as our budget is fairly limited. It’s a corner plot with room at the side.
Thanks for any advice you could offer. Thinking of 24* 16 feet ish
Thanks mel

mjackson says:

Hi Mel.

Please feel free to visit our online cost guide in order to get a rough price.

I hope this helps.

Mark @ Servicemagic

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