The average cost for single-storey house extensions in Chelmsford is £30,000, while the ballpark figure for a double-storey development is £45,000. These figures are based on an extension being 20 square metres in ground floor area. However, your development might be different, so how do you calculate the costs?

The rules, regulations and costs associated with house extensions in Chelmsford can be misjudged. With that in mind, it’s a good idea to get a clear understanding of the process and the costs involved when extending your home.

Your home is unique and your ideas for extending it are too, which means the cost of any building work will ultimately be determined by what you want. Obviously, single-storey, double-storey and loft extensions will differ in cost. However, this doesn’t mean that you can’t get a rough estimate of how much your extension will set you back.

In this blog we give you some general guidelines for calculating the cost of single-storey and double-storey house extensions in Chelmsford.

Single-storey house extensions in Chelmsford


It’s worth knowing that the starting cost of a single-storey rear extension in Essex is £30,000, based on building over an area covering 20 square metres. This is calculated by breaking down the cost per square metre. In the Chelmsford area the cost per square metre is usually £1500 to £2000 depending upon your specifications. For example, including a set of aluminium bi-fold doors will up the cost per square metre but the additional cost is often worth it.

When costing up your totals, don’t forget to add the following:

  • 10 – 15 percent for professional fees i.e. – architects, building regulations, planning applications and structural engineers.
  • VAT

It’s a good idea to get three quotes from local Chelmsford builders to determine costs and take the opportunity to visit the current and completed jobs that your chosen builders have worked on.

Double-storey house extensions in Chelmsford


The average cost of double-storey house extensions in Chelmsford is £45,000 (excluding professional fees and VAT). As a general rule, two-storey extensions (or more) do not cost double that of single-storey developments.

However, it’s recommended that you add 50 to 60 percent to the build cost of a single-storey extension if building a double-storey extension (provided that the two storeys are the same size). For instance, say a single-storey extension costs £30,000, adding 50 percent will increase your double-storey extension cost to £45,000.

Once again, don’t forget to factor in VAT costs and 10-15 percent for professional fees.

Planning a house extension can seem like a colossal task, but provided you’re organised and can figure out rough costs you can get your project off the ground. Remember, the first place to start is with those all-important costs.

Another cost to consider if you’re building close to a neighbour is that your extension will need to comply with the 1996 ‘Party Wall Act.’ A party wall settlement can cost around £700 per neighbour and if your neighbours approve of your extension in writing, you can avoid having to use a surveyor, keeping costs down.

Interested in how your extension will progress? Check out our Facebook page where you can see the process in pictures thanks to our most recent works. See the transformation stage-by-stage.

In part two, Grant Builders calculates the costs associated kitchen extensions. Watch this space.

Hire a Chelmsford builder for your house extension

Call us at Grant Builders for a free, no obligation quote on 01245 422226. Alternatively, get in touch using our online contact form.