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House extensions: everything a homeowner needs to know

This is an essential guide for any homeowner looking to add a house extension. We cover costs, finance, planning, regulations, and have plenty of inspirational ideas too!

14 min read

Why move when you can improve? With a home extension, you can get the space you need, while also being able to stay in the area you love. What’s more, with the right home extension, designed by the right architect, you not only get to enjoy the day to day benefits, but you may also find the value of your property benefiting too.

So, how do you go about creating a home extension?

In this ultimate guide for homeowners, we’ll be helping you explore your options. This will not only include showing you what home extension options you have, but diving deep into the ins and outs of getting your project on site. From planning to building regulations, budgeting to finance, we’ll be leaving no stone left unturned in this comprehensive guide.

Want tailored advice? Simply click here to book a FREE consultation.

Home extension types

Home extensions come in all shapes and sizes, so finding the right one for your property only requires a little bit of research. Here are some popular extension types you might consider…

Learn more about the types of house extensions available.

Ground floor extension vs first floor extension

If you’re in the fortunate position of having both a ground and first floor, you might be considering how best to extend your home. Both ground floor extensions and first floor extensions have various benefits that could transform your space. We’re going to explore them in a little more depth so you can decide which option is more suitable for you.

Ground floor extensions are fantastic for homeowners who are looking to open up the more social areas of their homes, such as an open-plan kitchen or spacious living room. This can in turn open up the opportunity to reimagine your home’s relationship with the outdoors if you have a garden by opting for design features such as bifold doors. Ground floor extensions are also a practical option if you or members of your household have mobility challenges so you can jazz up your interiors while making the layout easier to navigate.

First floor extensions are a great option if you’re looking to create an extra room that benefits from being separate from the rest of your home – think bedrooms, home offices and bathrooms. This can be particularly useful if you have kids and need either extra space for their nursery, a spare bathroom or a quiet place to work from home.

Ground floor house extensions can take longer to build and be slightly more expensive because of the foundational work required to begin the construction process. However, if you’re weighing up the cost and the outcome, both ground floor extensions and first floor house extensions will add value to your home and improve its practicality.

Front house extension

Extending the front of your home has the major benefit of keeping your rear garden intact. This extension can be used to enlarge your living room, create a new ground floor bedroom, or even just add in a new porch. However, as this extension will be visible on street level, it will be subject to more planning scrutiny.

Learn more about front house extensions.

Side of house extension

Situated to the (you guessed it) side of your house, this extension is a fantastic option for anyone looking to put a sad looking alleyway space to good use. A side house extension can be used to level off the rear of your home and create a compact new addition that transforms the property. Though small, these mighty extensions have been used to create some truly stunning open plan kitchen diners. What’s more, you might be able to achieve yours without the need for a full planning application.

Learn more about side of house extensions.

Semi-detached house extension

If you live in a semi-detached property, there are plenty of extension types for you to explore. With only one side of your property attached to a neighbour, you and your architect can extend your house in a way that doesn’t impact on the next door’s privacy or create any party wall matters. Semi-detached house extensions can also benefit from permitted development rights, which can help during the planning stage.

Learn more about semi-detached house extensions.

Terraced house extensions

It can feel a little daunting to extend a terraced house, but you needn’t be worried. Although you’ll need to factor in the privacy of your neighbours, along with their right to light, you will still enjoy plenty of design freedom. Of course, you should be aware that it’s likely your project will affect either a shared wall or boundary with one (or maybe both) of your neighbours. In this scenario, you will need to ensure you serve a party wall notice and get permission before construction begins.

Learn more about terraced house extensions.

Rear house extensions

Extending the rear of your house is a very popular option. Often used to expand key living areas, such as your kitchen, the rear extension is a highly versatile addition and can be used to create all kinds of space. You might opt for a new ground floor bedroom, utility room, home office, or even playroom. You may also use popular glazing, such as bi-fold doors, to create better connection to your garden space and bring lots of natural light into your home.

Learn more about rear house extensions.

Flat-pack house extensions

Flat-pack or prefab extensions are relatively newcomers on the residential scene, but have been rising in popularity over the last few years. Because they’re primarily built off-site, they’re a very cost effective way to extend your home and have much shorter construction times - meaning you don’t have to live on a building site or rented accommodation for very long. However, many flat-pack homes offer little to no customisation, and so you can lose one of the main benefits of extending your home, which is that you end up with a home tailored to your family.

Learn more about flat-pack house extensions.

House extension - a glass wraparound in London

House extensions costs

Before you start any project, it's important to work out a budget and a financing strategy. At Resi, our brokers can help you explore different lending options, simply click here to get started.

Overall, the cost of a house extension will vary massively depending on…

  • Extension type
  • Size
  • Design complexity
  • Location
  • Quality of materials and professionals used
  • Pre-existing site condition

That being said, below are some cost estimates for you to consider. Don’t hesitate to try out our Quick Quote Tool to get an idea of how much your project might cost or book a free advice call to talk us through your ideas in more detail.

Flat-pack house extensions Approximately between £750 and £1,140 per square metre on a budget, mid-range would cost between £1,275 and £1,800, and high-end would cost between £1,650 and £3,600.
Rear house extensions Ground floor: £40,000 - £100,000
Double-storey: £70,000 - £150,000
Terraced house extensions Approximately £1,200 to £3,300 per square metre
Semi-detached house extension Ground floor: £40,000 - £100,000
Double-storey: £70,000 - £150,000
Side of house: £50,000 - £90,000
Side of house extension £50,000 - £90,000
Front house extension Approximately £1,500 to £3000 per square metre.

Learn more about the cost of house extensions.

How much money can DIY save you on a home extension?

If you’ve got the skill set, doing things yourself can help save you thousands on a home extension. However, you should be cautious about the risks involved. Mess up a key element of your build, especially anything relating to structure, and the cost of repairs will likely cancel out any savings you made at the time.

Therefore, unless you’re qualified, we recommend you stay away from…

  • Roofing
  • Plumbing
  • Electrics
  • Demolition

Learn more about DIY and home extensions here.

7 tips to keep house extension costs down

At Resi, our home improvement experts have plenty of tricks up their sleeves to help you keep costs down.

If you're looking to reign in your budget, consider this advice...

  • Make pricing your project as easy as possible with a good measured survey and building regulations package
  • Properly assess your contractor quote
  • Thoroughly vet your suppliers and specialists
  • Consider adding a project manager
  • Research your materials
  • Think about moving out during construction
  • Get the right funding plan

Learn more: 7 tips to keep house extension costs down

A Resi house extension in Barnet, London

Financing a house extension

When it comes to financing your home extension, many people fail to do their homework and instead rely solely on their savings. But this is just one way of getting your extension off the ground. Make sure you’re also considering these alternatives…

House extension loan

For smaller projects, using an unsecured personal loan could be a good option, depending on the deals available to you at the time. They’re a great option if you’re only looking to cover short-term costs, as they don’t come with set-up fees attached. However, due to the high interest rates, you’ll want to make sure you pay this type of loan back quickly, as well as back sure you borrow less than £30,000.

Learn more about financing your house extension

House extension remortgage

For larger projects - over £30,000 - you might want to consider remortgaging or securing a further advance. This route is very attractive, as it can utilize both the existing and future equity of your home to get you the amount you need. What’s more, it also gives more flexibility than just using savings alone.

Personal savings

The benefits of using personal savings are obvious. With no lender involved, you needn’t worry about interest rates or payment plans. This is very appealing but there are some downsides to this approach. For instance, it can take time to get your savings to where they need to be and, during this time, inflation can go up, taking your project out of reach. Savings are also quite inflexible, putting you in a difficult position if you’re not budgeting a contingency fund at the same time.

Get tailored financial advice with Resi Finance

House extension ideas

House side extension with glass ceiling in Lambeth

A side home extension in Lambeth

Side extensions are a fantastic way to use up dead space around your property. Typically used to extend older housing stock, a side extension squares off a property with an alleyway present and expands key living areas.

This Lambeth project was completed in 2016, and used the side extension to create a broken plan kitchen/living room - complete with a glass ceiling and exposed brick wall.

A Crittall wraparound house extension in Southwark

A wraparound house extension in Southwark

Many people assume wraparound extensions have to be a massive undertaking, but as this Southwark project shows, they can be very economical. Rather than losing an entire alleyway or a large chunk of your rear garden, a wraparound allows you to take a little from both - resulting in plenty of space but without the sacrifice!

For this project, we combined the wraparound house extension with a matching brick facade and gorgeous Crittal french doors. This creates not only a beautiful kitchen diner, but leaves space to the side for raised bed and a picturesque view for the living room.

Get more house extension ideas by visiting our portfolio.

Interior design mistakes to avoid in your extension

When you’re focused on your architectural plans and securing planning permission, it might seem like the interior design of your extension is a problem for future you - but no! Trust us, thinking early on how you want the new space to feel and function day to day will help you avoid expensive mistakes and ensure you the space you always dreamt of.

We asked our interior design partners, My Bespoke Room, for the top design mistakes to avoid. First on their list was people not thinking about the final layout of the room and where key items of furniture will be. Problems arise when you move in and realise there’s a radiator where your sofa should be, or a sideboard with no plug socket nearby for a table lamp.


It’s also very common not to think about how the new extension will sit next to the original part of the house. It can be wonderful to have a big ‘wow’ moment as you enter the new space from the old but it’s still important to have a thread that joins them so it’s not completely jarring. You can do this by using the same flooring throughout or by using colours on the walls in the same hue e.g. light pastel colours that are all different but sit happily next to each other.

Another big mistake is not maximising the natural light in your new space. It’s so important to think about where the light will be throughout the day and what times of the day you will use the room. For example, an open plan kitchen, dining room will be in use throughout the day and so you’ll want to maximise light as much as possible. Living rooms however tend to be used in the evenings and so are better placed in parts of your home that aren’t flooded in natural light.

You can avoid expensive mistakes by hiring a professional interior designer from just £195 for their bespoke consultancy service. Book a free chat to discuss your project here.

Environmentally friendly house extensions

More and more homeowners are becoming more environmentally conscious, especially when it comes to their households. With our homes accounting for 27% of the UK’s carbon emissions, there’s no better place to start your eco-friendly journey. And, luckily, there are plenty of ways to make your home extension plans that little bit greener.

How to build an energy efficient house extension

One of the best ways to bring your carbon emissions down is to ensure your home uses energy efficiently. The three areas to focus on in this regard are…

  • Lighting
  • Heating
  • Insulation

Learn more about energy efficient home extensions here

What is the house extension process?

While each house extension is unique, it’s likely you’ll be running through the same list of tasks as your neighbours. Traditionally, this process has felt fragmented and confusing, but with services like Resi, you can sit back and relax, as our team guides you from Point A to Point B.

Get a free quote for Resi’s all-in-one service

Most projects will need to undergo these stages before they reach the construction stage…

  • Measured survey
  • Proposed design
  • Planning permission
  • Structural engineer
  • Party wall notice
  • CCTV surveyor
  • Building regulations package
  • Putting your project out for tender
  • Selecting a contractor

Do you need an architect for a house extension?

You are not legally required to hire an architect.

However, this doesn’t mean you should rule them out. Architects are highly skilled in home design and bring a range of benefits to any project. Some of the most important reasons to consider hiring an architect are…

  • Better design
  • More added home value
  • Expert guidance
  • Increased planning success
  • Plus more!

Learn more: Do you need an architect for an extension?

House extension drawings

Once you get started with your home extension project, you can quickly get lost in all the talk concerning drawings. What are elevations? Which do you need for planning?

For most projects, you’ll need the following types of construction drawings to get your project through planning and ready for construction…

  • Existing drawings
  • Design floor plans
  • Elevations
  • Structural drawings
  • Electrical drawings
  • Plumbing and sanitary drawings

Lean more about house extensions drawings and plans.

House extension regulations

When it comes to regulations, you better strap yourself in for a long ride. From planning permission to building regulations, structural drawings to party walls, there’s plenty of hoops you’ll need to jump through before you’re legally ready to start construction.

The main regulations you should focus on are…

  • Planning permission
  • Building regulations
  • Party wall matters

What kind of survey do I need for my house extension?

Surveying your property is one of the first steps of any project, and it is often underestimated how important this stage really is. By producing the existing drawings most of your team will use through the course of your project, getting a high-quality survey can make all the difference to both the results and your budget. Afterall, make a mistake here and resolving the error can be costly.

So, what kind of survey will you need? Your options will include…

  • Commercial grade laser surveys
  • Measured surveys
  • Hand-drawn surveys
  • Topographic surveys

Learn more: What kind of survey do I need?

House extension without planning permission

Can you build a home extension without planning permission? Yes!

If your project comes under your permitted development rights, you’ll be able to avoid the need for a full planning application. However, this doesn’t mean you’ll be able to escape the planning process entirely. It’s still highly advised you apply for a lawful development certificate, in order to document your project was legal at the point of construction. And, if you plan on building a large rear extension (up to 6m or 8m in length, depending on whether or not your home is detached), then you are legally required to apply for prior approval.

Permitted development rights are great for removing subjectivity from the planning process, but getting the right documentation will take roughly the same time as a full planning application, so if you’re looking to cut down on timings, think again! They also don’t cover all properties and come with strict design guidelines.

Learn more: house extensions you can build without planning permission.

Can I add an extension to a listed building?

Adding an extension to a listed building isn’t impossible, but your options will be limited.

Unlike other properties, you won’t benefit from permitted development rights, so a full planning application will be required. You’ll also need to obtain listed building consent, which will take into consideration:

  • History of the building
  • Character features
  • Measures you’ll take to protect key features
  • Size of your extension
  • Design of your extension

Learn more about adding an extension to a listed building

Securing party wall agreement for house extensions

If you share a boundary with another household, you may need to secure a party wall agreement – this could be a literal wall or even an outbuilding. Read this article to learn whether you might be required to secure a party wall agreement or book a free call with one of our planning experts.

Explore our guide to how to serve a party wall notice and give yourself the best chance of your work going ahead.

Get a design quote for your house extension

Which part of your property would you like to extend?

Ground Floor
First Floor


Which is the best type of house extension?

The best type of house extension for your home will rely on what you’re hoping to achieve – an extra room, maximum added value to the property, a reimagining of the layout? We recommend speaking to one of our experts about what type of home you have and what you’re looking to achieve with your house extension project.

How much does a house extension cost?

House extension costs vary hugely depending on the existing property, its location and the scale of the house extension project being proposed. We break down some of the costs in this article.

Do I need planning permission to extend my house?

Depending on what type and size of extension you’re hoping to get, you may be required to obtain planning permission. Speak to one of our experienced Planning experts to find out what steps you need to take to give your house extension project the best chance of going forward.

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