UK Architect

Room to Grow: Building a Rear House Extension in Manchester

Rear extensions are the most popular way to provide more quality space easily and on a tight budget. In this guide we will show you how.

Open plan house architect
Credit @Scott & Scott Architects

If you are a homeowner in Manchester then you may have been curious about the various improvements available to your housing in order to accommodate more space, why else would you be reading right now? Well, you're in luck, as one of the most popular options available is a rear house extensions and this guide can help you. Whether you wish to create living space for the family, add value to the property or rent the space out as a separate unit, we'll talk you through everything you need to know to build your rear house extension. 

What is Defined as a Rear Extension?

A rear extension - simply put - is a built form which extends from the rear wall of the existing property (where the opposite facade is the front entrance).

This definition of rear extension has many rules and allowances when it comes to planning permission and design with typical houses across the UK. 

As you may have seen in lifestyle magazines and online, these rear extensions are popular ways of creating large open plan living kitchen and dining spaces which connect seamlessly to the outdoors, normally a private garden. 

Image credit @Dfm Architects

modern house extension architect

How Far Can a Rear Extension Go?

How far you can build your rear extension and how big you can make it come down to a few things primarily:

- Your budget.

- Your requirements.

- The planning rules.

It is important to consider first what you need from your extension before immediately trying to build as large as possible.

There are no definitive rules when it comes to how far a rear extension can go, but as a general rule of thumb, it is usually difficult to get anything larger than half the size of the house.

It's also important to take into account any neighbouring properties and ensure that your new extension does not cause any obstruction or privacy issues for them. Always consult an architect when in doubt, and make sure to get planning permission and building regulations approval before you start any work.

If you are unsure how large you can build your extension. We're here for a free consultation.

Image credit @ArchitectureforLondon

timber frame house extension architect

How Long Does It Take to Build a Rear Extension?

Below is a rough timeline describing the total time is takes to build a rear extension.

2 to 4 weeks

Initial consultation to submission of a planning application

From your first consultation with us to submitting a planning application for your project, the average time taken is 2 to 4 weeks. This includes discussing and confirming your plans, drawing up the rear extension, revisions and submission.

6 weeks

Householder planning permission

After submitting a planning application, the council have up to 6 weeks to issue a decision. During this time we are opening a dialogue with the council to ensure your project has the best chance to be approved and to rectify any issues they may have.

The decision - in our experience - always comes towards the end of this deadline, it is also possible for the council to ask for additional time (usually 1-2 weeks).

4 weeks

Gain Building Regulations approval

Following planning permission, we provide extra detail onto the drawings in order to satisfy building regulation rules and show the design is up to standard. A structural engineer will be conducting the structural calculations and a building control officer will be checking everything prior to giving approval to start on site.

This stage normally takes 4 weeks before moving to construction on-site.

3 to 4 months


Your builder is now ready to start on-site. For a typical rear extension to a UK property, you can expect a timeframe of between 3 to 4 months. 

Bare in mind that where complexity arises, this time can increase, however, your builder should be able to provide an accurate estimation of time and budget.

6 to 7.5 months

Total Time

This means in total, you can expect your rear extension project to take 6 to 7.5 months to build from initial idea and approaching an Architect, all the way to completion.

What Is the Average Cost of Rear House Extension?

The cost of a rear extension - much like with the time it takes - will depend on the size and complexity of your rear extension. Any good architect will ask and confirm what you budget is for a project prior to starting work for you, this will mean the project can be designed accordingly.

Common items which can blow the budget for a rear extension include:

- Too many expensive fittings and fixtures - this can include items in the kitchens and bathrooms.

- Expensive materials - Whether these be on the inside or outside.

- A complex / overdesigned project with too many structural items - sometimes it can be easier and cheaper to use parts of the original building instead of creating large steel openings.

- Expensive glass products - Doors and windows can often be some of the most expensive products on a project, make sure to use them only where is most effective and necessary to your project.

Below is a construction cost calculator you can use to make estimations about the cost of your project.

modern design architect

Home Extension Construction Calculator

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

What Permissions Do I Need for a Rear House Extension?

This will vary depending on your location and the size of your project, but in most cases, you'll need to gain planning permission approval from your local council for any rear extension larger than 3 metres from the rear of the existing house.

In some cases, you may need permission - called a party wall agreement - from a neighbouring property owner to proceed with your project. Always check local laws and ordinances before beginning any construction work on your home!

Image credit @CAN

unique house extension design

Wrapping Up

A rear house extension can be a great way to add extra space and value to your home and with this guide you can achieve one on time and one budget.

Keep in mind that there are many things to consider when planning and designing a rear house extension as can be summarized in this guide. Always consult with professionals where possible before getting started with major stages of the work and good luck!

Image credit @kingsmeadconversions

loft conversion architect

Get Free Advice On Your Rear Extension Project. We offer professional advice for your next rear extension project. Fill out the form to get started.

architect logo

Tel: +44 20 8638 5243

© 2020, Sean Payne Arch Design limited company registered in England and Wales | Registered number: 12628241 | Registered office: 124 City Road, London EC1V 2NX