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How to Design a House Extension in the UK: A Guide for 2022

Designing a house extension can be an excellent way to design their dream home on a limited budget and without moving. Design however is not always straightforward, but luckily this guide will provide you the main steps you can take need to design your own extension.

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Credit @Will Gamble Architects

Why Start A Rear Extension Project?

A rear extension is a popular rear popular and practical option for the majority of homes in the UK. They can provide the aesthetic improvements for hosting guests alongside extra space for rooms such as bedrooms and offices.

Design Tips for House Extensions

When designing a house extension,
it is important to keep the following things in mind:

Integrate your old house with the new addition

Extensions should be designed with the existing home in mind. Try to create a design that flows well between the two spaces and looks like it was always meant to be there!

Make the space practical

Think about how you will use the space. A design that is flexible and can be adjusted in the future will save you time and money!

Try to add natural light where possible

A great idea is to add a skylight within the roof of your extension, as it helps provide natural light to your new project. This also allows more sunlight into your original house, something we always want with living spaces.

Consider the different seasons when designing your extension

For example, if you are adding a playroom at the back of your house, which would get lots of sunlight in spring and summer months, consider how it will impact living spaces during winter times!

Make your spaces flexible

If possible, try to design something that offers multiple uses so that you get the most out of your space. For example, a home office that can double as a guest bedroom when needed!


House Extension Costs in the UK

The cost of designing and building an extension varies depending on the size and complexity of the project. As a rough guide, you should expect to pay between £1900 and £2400 per square metre for a standard extension. Keep in mind that these prices can vary significantly depending on the location and contractor you use, so it is important to get several quotes before starting any work.

Some of the most common features that increase the cost of an extension include:

A pitched roof as opposed to a flat roof

An extra storey

A bay window

An extra bathroom or bedroom

Glass in the extension to let more natural light in

It is important that you use a reputable builder when designing and building your new home extension. This will ensure that the work is completed successfully, on time, and within budget!

If you want an estimate at the total construction cost for your project, try our calculator below.

Home Extension Construction Calculator

  • Construction Cost incl. VAT
  • VAT 20% Excluding VAT
  • Professional Fees Based on average complexity
  • Initial Consultation

How do I Design a House Extension in the UK?

Now that you have a general idea of what to consider when designing your house extension, it’s time to get started on the design process! The following steps will help you create a plan that is perfect for your needs.

Step One: Draw Out Your Ideas

The best way to start designing an extension is by drawing out your ideas. This can be done by hand or using a computer program like SketchUp, which is free to download online. Draw out the shape of the extension, as well as any features that you want to be included (e.g. windows, doors, etc.).

Step Two: Consider Your Requirements

Once you have drawn out your ideas, it is a good idea to consider your requirements. This includes sizes of key spaces, key features (e.g. an extra bedroom or bathroom), and where these features will be located within the extension plan.

Step Three: Consider the Locale

This includes the location the extension will be built in relation to existing structures, nearby trees and greenery (e.g. if you are building on a slope), what orientation best suits the needs of the space (south-facing for sunlight or north-facing for privacy) etc.

Image credit @DNG Studio

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Step Four: Find A Good Architect To Draw Your Plans

Once you have come up with some ideas for your house extension, it is time to find an architect. An architect will take your ideas and put them into a design that can be used by builders to complete the work on time and within budget! This type of service typically costs between £1300-£1900 for planning permission level design depending on location, so make sure you shop around for the best price before deciding who to use.

Having rough drawings will mean you can communicate your ideas far quicker and aid a reduced fee with an Architect. See our architect fee calculator below in order to plan for the fees you can expect.

Step Five: Get Quotes From Builders

Once you have the plans from your architect, it is time to get quotes from builders. This will give you an idea of how much the extension will cost to build. Make sure to ask for references and check out reviews online before deciding who to use!

Step Six: Start Building!

Once you have finalised your plans, it is time to start building! Make sure to keep in mind the estimated budget and timeline when doing so, as this will help avoid any costly surprises down the road. 

Step Seven: Enjoy Your New Extension!

Once the extension is complete, take some time to enjoy your new space! This could be anything from a home office to an extra bedroom – whatever works best for you and your family. Congratulations on designing and building your very own house extension!

Image credit @YARD Architects

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Architect's Fee Estimate Calculator

  • 1. Initial Consultation
  • 2. Planning Stage Pay as you go, 3 installments of
  • 3. Technical Drawings Pay as you go, 3 installments of
  • 4. Construction Management

Cost Tips to Save Money While Building House Extension

The best way to save money is to hire a good architect who knows how much materials cost and can help you avoid unnecessary expenses.

Try not to cut corners by doing the work yourself unless you are experienced and can get a professional opinion on your thinking and planning. In 99% of cases taking on too much planning yourself will end up costing you more in the long run because of mistakes or problems that will have to be fixed.

Compare prices for materials and labour to get the best deals, and be sure to get several quotes before choosing a contractor.

Make sure you have everything planned out in detail before starting construction, as this will help avoid delays and costly mistakes.

Be prepared for some disruption during the construction process, most problems can be minimized ahead of time but be aware of certain items which do not reveal themselves until you've started the work.

Finalise each stage of construction making sure each item has been checked and confirmed as built correctly. This will minimise  disruption and save money.

Image credit @Matthew Wood

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Design is all About Planning

Designing a house extension can be a costly and disruptive process if not planned correctly, much of design - in a way - includes this.

By following the tips in this guide, you will be able to get started designing your own rear extension in an organised fashion which will save you money and time later down the line. 

Image credit @Erbar Mattes

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