How much does a house extension cost in London (2022)?

How much does a house extension cost in London? The article explores house extension costs, along with tax considerations and other typical related costs. It explains the options that are available for various budgets and outlines the best approaches to making savings. Building a house extension is often cheaper than upsizing and avoids the stress of moving. London extensions do however have a cost premium when compared to the rest of the UK. This is due to higher labour and material costs, and the difficulties of compact construction sites.

While there are many factors that could affect the cost of an extension in London, the most important factor to consider is the size of the extension. This is because size (generally measured as floor area) directly correlates with the total cost of the project.

House Extension Costs in 2022

There may be planning policy issues to be aware of when deciding the size of your extension. Your architect will be able to advise you of the likely maximum size possible under permitted development regulations (if relevant) or with a planning application for your property.

Once you know the required size of your extension, we can begin to estimate costs using some standard square metre rates. All of the guideline prices listed below are for construction only, updated as of 2022. They do not include VAT or professional fees.

House extension costs:

  • Single storey – A single storey extension in London will usually cost between £2,000 and £3,000 per sqm (£185 and £280 per square foot). £2,000 per sqm would represent cost-effective finishes and products. 
  • Two storey – To approximate the cost of two-storey extension, add 50 to 60% to the guideline price of a single storey extension. There are economies with two-storey extensions as only one set of foundations is required for example. Two storey extensions can be more complex to achieve planning consent for.
  • Basement – Due to construction complexity and risk, a basement is more costly. A basement extension in London will typically cost between £4,000 and £5,000 per square metre (£370 and £465 per square foot).

What will the extension be used for?

Many people include a kitchen or a bathroom in their extension plans. These will naturally increase the overall cost when compared to additional bedrooms or living spaces.

  • Kitchens – If you are looking to add a kitchen as part of your extension, then expect to pay an additional £15,000 to £40,000. £15,000 will typically cover a low to mid-range design complete with units and some appliances.
  • Bathrooms – The additional cost for a bathroom will begin at around £5,000 to £10,000. The price will increase based on the quality of fixtures and fittings.

Other Costs

Consultant & Statutory Fees
The cost of all professional services and other statutory fees will typically be 15%-20% on top of the construction cost.

The planning application fee for house extensions is £206 + an admin fee of around £25 – 30. Some house extensions will not require planning permission, as they may fall under Permitted Development. In this case, it is still advised to apply for a Lawful Development Certificate which confirms that the works do not need planning. This is particularly important if you plan on selling after completing the works. A prospective buyer is likely to expect proof that the works are lawful.
The application fee for a Lawful Development Certificate is half the planning application fee.

Many home insurance policies will not cover you while there are building works. This could potentially leave you liable should there be any structural damage during renovations. Therefore it is important to notify your insurers before beginning work and you may also need to take out an additional policy while construction is taking place for your peace of mind. For example, non-negligence insurance can help to protect you, should there be any structural damage to your neighbour as a result of your extension.

Extensions usually attract a full VAT rate, currently 20%. There are some projects where the rate of VAT will change. For example, any property that has been vacant for more than two years may be eligible for a reduced VAT rate of 5%.
If you have any questions on the applicable rate of VAT on your project, it is always best to seek professional advice from a VAT consultant.

Visit G4 Design & Build's Projects page to view our recent house extensions. You can also contact us on 02034884208 to discuss your project.