Your Complete Guide to Extending Your Home

Posted 21 January 2019 by Nick Parkhouse

Thinking of a home extension? Here’s your complete guide to how to build an extension, planning permission and costs...

If you need more space in your home but don’t want to move, an extension is the perfect option. Whether you want a simple conservatory or a more ambitious two-storey extension, adding extra rooms can both add value and give you more living space.

But how much does an extension cost? What planning permission do you need? And how do you choose a builder? Keep reading for answers to these questions and more in your complete home extension guide.

How much does an extension cost?

Extensions come in all shapes and sizes and so the cost will depend on a range of factors including:

  • Size
  • Specification
  • Location

Depending on where you live, experts suggest that an extension will cost between £1,000 and £2,000 per square metre. You can expect a single storey extension to cost:

  • Basic quality – £1,000 to £1,680 per square metre
  • Good quality – £1,680 to £1,920 per square metre
  • High quality – £1,920 to £2,160 per square metre.

If you are looking for a two-storey extension then you should expect to pay a little more, as you will have to add the cost of walls and floor joints.

Raising the money to fund your extension

One of your considerations will be ‘how do I fund an extension?’ There are five main ways that you can raise the cash you need:

  • Savings – use money you have already saved to fund your extension.
  • Additional loan on your mortgage – you can approach your existing mortgage lender to borrow additional money against the value of your home. You may have to go through an underwriting process to ensure the loan is affordable.
  • Remortgage – you can switch your mortgage to another lender and simultaneously borrow an additional sum to pay for your extension. You may also get a more competitive deal on your main mortgage. Read our complete guide to remortgaging
  • Secured loan – Many lenders offer ‘secured’ or ‘second charge’ loans against your home. These can be useful if your mortgage lender won’t agree additional borrowing or you don’t want to remortgage.
  • Unsecured loan – unsecured loans are not based on your property value. Your payments are likely to be higher as rates are typically more expensive and you’ll probably have to pay the loan back over a shorter period than a mortgage.

Make sure you have the necessary planning permission

Depending on the size and specification of your extension, you may need to obtain planning permission for the work.

You don’t need planning permission if your extension project falls within your ‘permitted development rights’. This means:

  • The rear wall of a detached home can be extended by 8m if it is a single storey property and 3m if it is two storeys.
  • The rear wall of a semi-detached or terraced house can be extended by 6m if it is a single storey and 3m if it is two storeys.
  • A single storey extension can’t be higher than 4m in height to the ridge and eaves, and ridge heights can’t be higher than the existing property.
  • Any two-storey extensions must not be closer than 7m to the rear boundary.

Generally speaking, you will need planning permission if:

  • You are extending beyond the measures above
  • Your house is listed or in a conservation area
  • You are increasing the overall height of your home
  • You are planning to use materials that are different from the original style of your home
  • Your extension covers more than half the area of land surrounding your home
  • You are extending towards a road.

You will also have to ensure that all building and fire regulations are adhered to.

Talk to your neighbours when planning an extension

If you are planning a building project, you can avoid issues with your neighbours by speaking to them first.

Let them know about your plans, particularly if there is likely to be noise, disruption, or additional traffic in your street. If you live in a semi-detached or terraced property and share a party wall, you’ll also need to speak to your neighbours as work may have to comply with the Party Wall Act.

There may also be features to your extension that will affect your neighbours. Examples include upper-floor balconies, windows overlooking their home or garden, and overshadowing.

How to choose a builder for your extension

Getting the right tradesman is the key to a successful extension project. So, when you compare builders make sure you:

  • Shop around. Get three or four quotes for the work, but don’t concentrate entirely on price. Ask builders about other projects they have carried out locally and speak to these homeowners to ask them about their experiences.
  • Ask for recommendations. Speak to friends and neighbours, head online for reviews, and speak to trade bodies such as the Federation of Master Builders.
  • Ensure the right warranties are in place. A good builder will offer warranties such as Masterbond.

Make sure you get the right insurance

During an extension project it is wise to take out extension insurance to cover the new works and the existing structure. This is because home insurers will often exclude any loss or damage that you suffer during renovation and extension works.

Insurance covers both your existing home and the new works. For example, it would typically cover you if your existing house collapsed while the builders were creating a new opening.

You may also want to take out insurance/a warranty on the new extension.

There are specialist insurance providers operating in the UK, so shop around online to find the right cover for you. Make sure you’re covered from the day the work starts until the project is completed.

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