What to consider when planning a house extension

With UK house prices continuing to rise, many homeowners have decided to opt for extending parts of their existing property over buying a new one, making house extension one of the most popular home improvement trends in recent years.

Extensions create much more space, can revitalise a home and saves the immense time and stress that is associated with moving. Moreover, home extensions have been found to increase the value of a property by up to 20 per cent, making it an ideal investment for those who may be planning to sell some years down the line.

The Market Design and Build, a UK-based design and build company, discusses several vital points to consider when planning a house extension.


Quality extensions do not come cheap, so it is important to set a sensible budget for the design you wish to achieve. Discuss your plans with an architect, designer or design and build team, who will help you match your project requirements with your budget. These people can create an effective planning strategy, as well as selecting an appropriate build team for the project.

A general guide for costs of single-storey extensions per metre-squared and based on quality is as follows:

  • Average: £1,000-£1,680
  • Good: £1,680 to £1,920
  • Excellent: £1,920 to £2,160

Of course, the overall cost of an extension will vary from project to project, with several factors affecting price, including location, size and other specifications.


Many people make the mistake of assuming that they can rely on home insurance or a builder’s public liability policy to cover their extension project, but this is not always the case. Most home insurance policies do not cover loss or damage when the home is undergoing renovation.

Because extensions are normally quite big projects, it isn’t unheard of for properties to become damaged when walls are knocked down, or electrical, gas or water supplies to be altered. Moreover, contractors are coming and going, which reduces levels of security.

As such, before you make any commitments, you should inform your insurance provider of the proposed extensions to determine whether you are covered. If you are not covered, then you must take out a special type of insurance which does cover extensions, and can adequately protect the new works and your existing structure. This policy should be in place during the initial project stages, right up until the point you complete the project.

Planning permission

In most cases, planning permission will not be necessary, as the majority of extensions will fall under the Permitted Development rights, which allow homeowners to improve and extend without planning permission. Guidance on these rules can be found here.

However, if you wish to undertake a significant extension, planning permission will probably be required, in which case, an application to your local authority needs to be submitted. Doing this as soon as possible is wise because it gives you time to consider other courses of action if you know your project is likely to be disproved.

Building regulations

Regardless of whether you require planning permission or not, all extension projects must gain approval under the Building Regulations. This is extremely important, as if the building regulations are not complied with, the contractors carrying out the work can be fined and prosecuted. Your local authority also has the power to charge you for any faulty work that requires fixing.

Moreover, if you wish to sell your home in the future, it will be tremendously difficult to do so without the certificates of compliance needed.

Finding the right people for the job

Selecting the right company (or companies) to execute your plans and carry out the work itself is extremely important – you are spending a lot of money on this, so you need to be happy with the result.

Undertaking a significant amount of research, asking for portfolios or case studies of previous work, and, if possible, speaking to past clients, will help you narrow down a list of suitable designers, structural engineers and builders to work with.

A designer will be able to help you draw up your project plans and submit them for approval (if necessary). A structural engineer is there to produce the calculations and drawings before approval under the Building Regulations, as well as the tender documents for the builders.

To find the right builder for your job, speak to people locally for recommendations, or visit a trusted site like Checkatrade, which provides detailed reviews from past clients.

Alternatively, you can hire a design and build team to handle the entire project for you, which many people find removes the stress of having to deal with multiple parties.

If you want to discuss a London house extension, visit www.themarketdesignbuild.com for a free quotation, or call 0203 432 5269.