Planning for a double storey extension

If you’re looking for more space but you don’t want to move, a double storey extension could be the answer. And this comprehensive guide will help you with your planning.

A double storey extension can transform your home, create usable spaces, and add value at the same time.

It just requires the right planning and preparation. And we’re here to help you understand what you need to do for a successful build.

Keep reading to find out everything you need to know…

Benefits of a double storey extension

If you’re already considering a double storey extension, chances are you can think of a few reasons why it’s a good idea.

But, just in case you’re still on the fence, here are some of the benefits of building a double storey extension:

• It adds value to your home up to 20% of the value of the property

• Buyers are often more attracted to homes with extensions as it saves them the hassle of carrying out the work

• You gain valuable extra space for you and your family to live in

• Two floors means double the space of single storey extension with minimal impact on your outdoor space

• You can maximise the use of existing structures by adding a storey on top of a garage or single-storey part of your property

• More space means more options for how to use your home – the options are endless

Step 1: Plan for your extension

To help you plan your double storey extension to perfection, we’ve put together this comprehensive guide for you…

1. Apply for planning permission

Due to their size and impact, most double storey extensions don’t fall under Permitted Development rights.

That means you’ll probably need to apply for planning permission before you get started.

Criteria for Permitted Development Rights for double storey extensions

You may be able to build your double storey extension without planning permission if…

• The extension doesn’t extend beyond the rear wall of the original house by more than 3 metres and is within 2 metres of a boundary

• It doesn’t exceed the highest part of your existing roof structure at any point

• The height of the extension eaves does not exceed the height of the existing house

• Your new extension doesn’t overlook your neighbours

• All the materials used for the new extension are similar to those of the existing property

Other criteria may apply to your property so we always recommend consulting with your local planning office first.

Lawful development

Even under Permitted Development, applying for a Lawful Development Certificate (LDC) can be a good idea.

Getting an LDC confirms that the building and the construction work did not require planning permission.

Leasehold vs freehold

Before you start planning or designing your new double storey extension, you need to check if you’re the freeholder of the property.

If you own the leasehold, not the freehold, of your property then you’ll need to check your lease details.

As the leaseholder, you’ll need to speak with your freeholder to get their consent for your proposed extension.

Leasehold vs Freehold: Which is best?

Discover more about leasehold and freehold properties with our handy guide. Including definitions, their differences, owning shares and essential guidance.

Learn more

When do I need planning permission?

If the double storey extension you’re planning to build doesn’t meet the above criteria, you’ll need to apply for planning permission.

Here are some of the reasons planning permission might be required for a double storey extension:

• It doesn’t meet the criteria for a Permitted Development

• Your property is in a restricted area, such as a Conservation Area

• The extension is going to significantly change the appearance of the property or local environment

• It’s going to negatively impact neighbouring properties

2. Adhere to Building Regulations

Every double storey extension built in the UK will need to comply with current Building Regulations.

That means your extension needs to be built in such a way that it proves to be structurally sound, energy-efficient, accessible, and safe to use.

You have two options here...

You could brush up on your Building Regulations and work closely with all tradespeople to ensure they’re carrying out the work properly.

Alternatively, we would recommend hiring tradespeople who are registered with a Competent Person Scheme…

Competent Persons

Competent Persons can self-certify certain types of building work to confirm that it meets the relevant regulations.

This saves you from having to get your local council or a private approved building inspector to check and approve your extension.

3. Inform your neighbours

Whenever you’re carrying out major work on your property, we recommend telling your neighbours about your planned work.

By maintaining good communication with your neighbours, they’re more likely to be on board with your plans. And less likely to complain about future disruption.

Party wall agreements

If your double storey extension involves building work near or on a wall shared with your neighbour's property, you’ll need a party wall agreement.

Learn more in our handy guide: Do I need a Party Wall Award for an extension?

4. Update your home insurance

Building a double storey extension will likely affect your home insurance and your premiums may change as a result.

Always inform your home insurance provider of any major changes to your property to ensure your policy remains valid.

5. Decide on your project management

A double storey extension project will need careful coordination so you need to decide who will manage the project – you or a professional project manager.

Unless you have the experience, skills and time to dedicate to the project, we recommend hiring a professional to manage your extension. Here are some professionals who can help.

• Architects

• Interior designers

• Project managers

• Extension builders

Need inspiration? Take a look at some of our favourite double storey extension ideas.

Step 2: Prepare your budget

With a project the size of a double storey extension, it’s important to understand all the costs involved.

You need to research costs and shop around to ensure you’re paying fair and competitive prices for the work.

As a rough guide, below are some average costs for a double storey extension in the UK:

• Double storey extension – £1,900 - £2,575 per m2

• Extension planning drawings – £950

• Surveyors fees – £1,250

Learn more about prices in our dedicated guide to double storey extension costs.

Compare costs for different extension types

You might start with the idea of a double storey extension, but plans can change. That’s why it’s important to research the different options.

And, when it comes to budgets, the total cost of an extension will vary a lot depending on the size and scope of the project.

To find out more about extension prices, below are some other useful guides that are worth reading:

• House extension costs

• Side return extension costs

• Garden room extension costs

Tips for staying on budget

Big home improvement projects like building an extension have a lot of elements, which can quickly impact your budget.

That’s why it’s important to keep on top of your spending. Here are some of our top tips for staying on budget:

• Always decide on your budget in advance

• Add a 20% contingency fund for unforeseen expenses

• Get multiple written quotes that include labour, materials and VAT to avoid surprises

• Try to make design decisions upfront about flooring, tiling, fixtures and fittings, and decoration

Step 3: Find the best local tradespeople

When it comes to finding the best tradespeople in your area, you’re in the perfect place.

We work hard to give you peace of mind that hiring tradespeople from Checkatrade is the right move:

• Every Checkatrade tradesperson has passed up to 12 checks

• We verify our members’ reviews so you can be confident you’re hiring reliable tradespeople

• When you find and book a tradesperson with us, we'll guarantee their work up to £1,000. Guaranteed for 12 months – Eligibility and T&Cs apply.

To get started, enter your postcode in the box below and browse a list of highly-rated tradespeople in your area.

You may also want to check out our collection of hiring guides that offer tips for finding specific tradespeople near you.

Step 5: The build process

Once you’ve done all your preparation, it’s time for the building work to start. Here’s an overview of the key steps in the process…

1. External construction

With approved plans and a team of experienced tradespeople ready to go, the construction phase begins. This involves:

• Preparing the site, e.g. erecting scaffolding, installing skips, setting up toilet facilities and other tools or equipment

• Carrying out groundwork and digging foundations

• Installing gullies and soakaways

• Building the structure, including walls and roof

• Installing windows and doors

• Adding downpipes and connecting to the drainage system

2. Interior building work

Once the main external structure of your double storey extension is complete, it’s time to work on the interior spaces:

• Reconfiguring your internal space, where necessary

• Removing redundant internal fixtures and fittings

• Installing insulation

• Building a new staircase, if needed

3. Internal fit out

With the interior building work complete, attention is turned to the functional details of the extension:

• Plastering walls and ceilings

• Laying flooring

• Adding utilities, including plumbing and electrics

• Installing new fittings and appliances

4. Interior decor

The building phase is done, and it’s now time to turn your blank canvas into the extension of your dreams. This is the fun part! Now you’ll be able to organise:

• Painting and decorating

• Bespoke furniture and storage

• Lighting schemes and fixtures

• Final interior design touches

5. Final inspections

There are just three last things to do:

• Manage any snagging issues with your contractors

• Arrange for final inspections to ensure that your extension complies with all safety and building regulations

• Relax and enjoy your wonderful new double storey extension!

Double storey extension checklist

• Building a double storey extension provides extra space, attracts buyers, and can add up to 20% value to your home

• Always check planning requirements with your local planning office

• Ensure your extension complies with the relevant building restrictions

• Let your neighbours know your plans and obtain any necessary party wall agreements

• Inform your home insurance provider of the changes to your property

• Take time to research costs and plan a budget – and keep on top of spending

• Use reliable sources like Checkatrade to find experienced and qualified local tradespeople for your project