Rear Extensions – What You Need to Know About Planning One

Extending your home can be a great idea, but before you dive in, check out this expert advice detailing what a rear extension entails

Full article first published on Houzz
Cathy Rebecca, Houzz Contributor

Extensions are a great way to improve your home and expand your living area without having to go through the rigmarole of moving house. With space often tight for families across the UK, particularly in our cities, extensions offer a potentially neat solution. While they are no light undertaking and require a decent amount of capital up front, they can be a savvy investment and may well pay for themselves and more when you come to sell your home. Here, three architects share their expert advice on things you should know about the extension process.

Professional advice from: Robert Maxwell, director of Maxwell & Company Architects Hugo Tugman, founder of Architect Your Home Jerry Evans, architect and principal of Southpoint

Types of extension

There are three main types of extension found in British cities: the rear extension, the side return extension and the wrapped extension. ‘A rear extension is one that goes across the full width of the property – from garden wall to garden wall – out towards the garden,’ says Robert Maxwell.

A side return extension makes use of the awkward space at the side of the rear projection on Victorian and Edwardian homes. ‘Some properties already have a closet wing with a small alleyway on the side of the property. Side return extensions incorporate that alleyway into the property and extend the closet wing to the full width of the property,’ says Robert.

A wrapped extension runs across the side elevation and back of the property and can be either single or two storey.

‘The most common type of extension is a single storey to the rear of the home,’ adds Hugo Tugman. ‘Victorian and Edwardian properties can feel very cellular. By extending out you can link the areas together and create a bigger, more open space. It can add a great deal of value to the home, make it more pleasant to be in and, if done well, can bring in a lot of daylight.’

Browse 10 creative ideas for side return extensions

Permitted development rights

Many councils allow for extensions under what is called permitted development, meaning you do not need to seek Planning Permission. There are documents you can download from local councils and RIBA (Royal Institute of British Architects) that explain exactly what you can do under permitted development.

You’re allowed to extend your home by a percentage of the volumetric space. ‘This includes all possible extensions to the property, so things like loft extensions, too,’ says Robert Maxwell. ‘You can send what is called a pre-application – an initial sketch and calculation of volume of the proposed property to see whether you are within the permitted development. This doesn’t have to be particularly refined, and many people choose to do this themselves,’ he explains.

Planning Portal outlines all of the rules with which extensions need to comply,’ explains Jerry Evans. ‘Things like size, height and distance from the road are all regulated.’

Read what to consider when planning a loft conversion

‘It’s extraordinary how much people can be confused by permitted development. You have to stay within quite a complex set of criteria to ensure you don’t step outside it, and local authorities can be quite unhelpful because they don’t want you to sidestep their consultation,’ says Hugo Tugman. ‘It’s absolutely worth getting in a professional at that early stage. In knowing exactly where the limits are, they can do extraordinary things and make enormous changes without requiring Planning Permission.’

Planning Permission

If your property doesn’t fall under permitted development, you will need to apply for Planning Permission. ‘There’s nothing to stop you applying for Planning Permission yourself, but you will need scale drawings of plans, elevations, a section through the building and its relation to surrounding properties,’ says Jerry Evans.

If you don’t have the expertise, you will need to contact a professional. ‘Most people go through the recommendation of a friend or research on a website such as Houzz,’ says Robert Maxwell. ‘From my point of view, it’s better to seek advice in the early stages, as architects can have a valuable input into the design of the space.’

Conservation areas

Where a property is in a conservation area, permitted development is not allowed and Planning Permission is more stringent. You can check with your local planning authority online to see whether or not you are in a conservation area – most city centres are.

‘If a local planning authority is trying to maintain the look and feel of a particular area, they designate it as a conservation area. They don’t want people to adapt the buildings so the cityscape changes,’ explains Robert Maxwell.

Get more inspiration from these exterior photos

The design

Architects can help you with the design and technical drawings of your extension. ‘The architect will first discuss the initial fee package. In the early stages, this might be an hourly rate, until it becomes clear the project is feasible,’ explains Robert Maxwell. ‘He or she will then come up with concept design sketches. Once the client is happy, they will produce detailed design drawings and a specification.’ These can be used for Planning Permission if required.

Using an architect

Architects can help with everything from initial design sketches to full project management. ‘We offer our services on a menu, so a client can go as far with us as they want,’ explains Hugo Tugman. ‘Some just want initial advice on the design, while others want help with permissions and regulations. Others still want us to project manage the whole thing. The more you use us, the more it costs… but the more control you have over what you get and the eventual price. We help people to avoid pitfalls and getting ripped off. Having an expert on board gives you weight when dealing with contractors and builders.’

‘The more detailed the drawings and the more tied down the specification, the lower the risk of overruns, which is one of the biggest reasons costs escalate,’ says Jerry. ‘An architect comes up with a fixed scheme and makes it clear exactly what is required and expected from the builder. The more you spend on drawings and specification, the more you take risk out of the project,’ he adds.

Building Regulations

All changes will need to adhere to strict Building Regulations, which are entirely separate to Planning Permission. ‘To get through Building Regulations, a building must meet rigorous standards,’ says Hugo Tugman. ‘A structural engineer and inspector will need to be brought in to approve final plans from a technical perspective and ensure they are structurally safe with proper drains.’

‘The Building Regulations for energy efficiency are quite strict, certainly in terms of glazing,’ Jerry says. ‘You struggle to get highly glazed extensions without going to very expensive triple-glazed units, and the Building Regulation standards for energy efficiency are going up all the time.’

Informing your neighbours

Planning law specifies that neighbours do not need to be informed for permitted development, but for the sake of your relationship with them it is always wise to let them know well in advance.

Where Planning Permission is required, it’s another story. ‘If you do need Planning Permission, your neighbours will be notified by the planning office,’ says Hugo Tugman.

Separate to Planning Permission is a party wall consent process, which you will likely have to go through. This might be done very amicably through a waiver letter, or your neighbours may request you get a party wall surveyor in, which can take more time and there is a cost involved. ‘The party wall process comes after Planning Permission has been granted as it requires a clearly detailed drawing,’ Hugo explains.

Putting your project out to tender

The tender is the package of information given to builders that they then use to get specifications from their suppliers for everything, plus their overheads and profits. Many people choose to take the drawings and specifications from the architect and manage the tender from there. ‘My strongest advice is do not go to just one builder,’ Hugo Tugman stresses. ‘The variation in cost is outstanding and will often be more than 100%. Send out the tender to at least four builders.

‘My second piece of advice is don’t go to a builder too early – you must have everything absolutely clearly specified and outlined first. To get a good comparison, the builders need to be pricing exactly the same thing, so don’t allow for any wriggle room. If your drawings are woolly, a builder can tell you what you want to hear, because there’s no solid information to hold them accountable to.’

Contractor-led projects

You don’t need to get an architect involved when planning your extension if you don’t want to – it’s possible to hire contractors and oversee the project yourself. ‘Many people have gone through the process without an architect successfully,’ says Hugo Tugman. ‘The danger is when you don’t know what you’re doing – you may not see the pitfalls that we would see and it can quickly become very expensive if you have to keep making adjustments.’

Cost-wise, however, consider the build as a whole. ‘With smaller projects, the architect fees can become a large part of the cost,’ Jerry says, ‘so it doesn’t always make sense to get an architect involved with a standard extension.’

Building materials

There are a number of materials you can choose for your extension, from glass, timber cladding and brick, to more exotic choices such as zinc and copper cladding.

‘There are two main approaches when it comes to choosing building materials,’ says Jerry Evans. ‘Some prefer to stay in keeping with the rest of the house, while others want a total contrast. This will determine which materials you decide to use.

‘There’s obviously an aesthetic element,’ Hugo says, ‘but other things to think about are cost and the environmental side of things. Using brickwork is much more expensive than block work and render, for example.’

Dealing with disruption

You should be prepared for a significant amount of disruption during the extension process. ‘There will be noise and dust, but what gets most people is the sense of intrusion,’ says Hugo Tugman. But the pain is usually worth the gain. ‘My wife likens it to childbirth – difficult to go through but well worth it. A typical single storey extension should take around 2-3 months, but some projects might be as quick as 1 month and others might take 6 months or longer.’

Be prudent

‘You can easily go overboard with extensions,’ warns Jerry Evans. ‘Throwing lots of money at it doesn’t necessarily mean you’ll get it back. Value added depends on where you are in the country. Where space is at a premium, of course it will add more. But it’s quite a dangerous game if you don’t know what you’re doing,’

He advises speaking to a local estate agent to get a rough valuation of how much they think it will add, and factor that into your budget. ‘It’s important to assess your property in relation to its location,’ adds Hugo Tugman. ‘It might become the most expensive property on the street, but it will reach a ceiling value.’


Come along to Grand Designs Live to get your project off the ground and book your free 30 minute consultation with one our experts in our Ask an Expert section to help you with your own extension.


Article provided by Houzz
Houzz is the leading platform for home renovation and design, providing people with everything they need to improve their homes from start to finish – online or from a mobile device. From decorating a small room to building a custom home and everything in between, Houzz connects millions of homeowners, home design enthusiasts and home improvement professionals across the country and around the world.

houzz l rgb

Newsletter Signup