Rear Extensions: Design & Cost Guide
A rear extension can transform your living space. Discover design ideas, cost estimates, and planning tips for adding space to the back of your home.
When it comes to home renovations, few projects can add space and value like a rear extension. The idea of extending your living space to get more natural light and blend with your outdoor space has captured the hearts of many homeowners. But a rear extension project requires careful planning and thought.
A rear extension is an addition to the back of a property that adds living space, often used for kitchens or family rooms. These extensions can increase functionality and flow, creating a seamless link between indoor and outdoor spaces.
Knowing the different types of rear extensions and what’s required for your property type is key to a successful build. From detached to listed buildings, each scenario is different and presents its own challenges and opportunities. And being aware of the benefits, design considerations and costs involved will prepare you for what’s to come.
This guide will help you plan your rear extension project, covering everything from design and permissions to budget and professional help. By reading these basics you can make informed decisions that will lead to a successful and happy project.
A rear extension is an intelligent addition to a property, often into the garden space. Of the many types, single storey rear extensions are the most popular as they are the simplest way to add more living space—perfect for an extra bedroom, a larger kitchen or a multiform room that can adapt to the homeowner’s lifestyle. For those who want to add to their home without the upheaval of moving, rear extensions are a valuable investment in both property value and quality of life.
The cost of a rear extension project varies depending on many factors, including the scope, materials and professional fees. Choosing from the common rear extension designs—single storey, two storey or first floor—depends on the current layout of the property and the homeowner’s requirements.
But these extensions aren’t without formalities. Planning permission may be required and it’s worth checking development rights or speaking to the local planning authority. Building regulations approval is mandatory and homeowners may need to negotiate a party wall agreement if the extension is near their neighbour’s boundary wall.
In summary, rear extensions are a solution for homeowners who want to add to their living space without moving home.
Rear extensions are a popular home improvement, they offer many benefits to homeowners. Not only do they give you more living space—larger kitchens, dining rooms and comfortable lounging areas—but they can also add value to the property—a good long term investment. Compared to the paperwork involved in moving house, a rear extension is a doddle and often a stress free process.
One of the biggest advantages of a rear extension is the ease of getting planning permission. As these extensions don’t alter the front of the house planning authorities are more likely to approve. And a single storey rear extension doesn’t require stairs so it’s more accessible for all occupants and avoids the complexities of maintaining the exterior of the property.
In summary:
These are the benefits of rear extensions for homeowners who want to add to their living space and property value.
Detached houses being standalone have fewer boundary and party wall issues. Extensions up to 4 meters are allowed under lawful development so the planning process is easier. This freedom also means more choice in design and materials. Rear extensions in these homes can be designed to capture garden views and create a peaceful and private living space.
Semi detached homes with shared walls require more consideration when extending. Single storey rear extensions can be up to 3 meters without full planning permission, but going beyond that up to 6 meters requires permission through permitted development rights. Extensions must be designed to comply with height restrictions and be in keeping with the existing property. Party wall agreements may be required if the work affects the shared boundary.
For terraced houses extensions can lighten and expand the compact spaces. Single storey extensions up to 3 meters can be built without planning permission and will make a big difference to the inside of the property. Two storey extensions require consideration of the neighbouring properties’ access to light. Glass features like skylights and bifolding doors are popular to bring light into these extensions and transform the living space.
Rear extensions on listed buildings are a sensitive operation and require listed building consent. Success depends on matching the original style and materials and not detracting from the historic character of the building. The journey to approval can be rocky with design revisions or negotiations so it’s important to take a thorough and respectful approach to extending these heritage assets.
When extending to the rear of a property homeowners need to consider several key design elements to get the new space to meet both aesthetic and functional needs. Since rear extensions are in empty space in the rear garden they allow for big additions that retain garden space and existing plants. The orientation and positioning of the extension can make a big difference to the internal layout and the relationship with the outside space so planning is key.
The visual impact of a rear extension is usually minimal from the front of the house which can make it an attractive proposal for planning permission. Local councils tend to view the retention of the original front of the house positively which can be a deciding factor in the planning permission process. In fact the discreet nature of rear extensions often gets a more favourable review from the planning authorities.
For those looking to add a lot more living space a two storey rear extension can add huge value, with an extra bedroom above and more living space on the ground floor. However double storey extension projects require careful consideration of overshadowing, overlooking and impact on neighbouring properties as they need to comply with privacy and daylight standards.
Professional design and planning permission for a rear extension can take as long as the build itself. Typically the whole project can take around a year to complete, from design conception to planning permission application to the build. Note that timelines can vary depending on the complexity of the project and the planning authority’s response.
The key considerations set the scene for a successful rear house extension, matching the new build to the homeowner’s brief and the regulations and guidelines.
Space planning is critical in a rear extension to get the most out of the space and the aesthetic. Homeowners often want to increase the living area, with bigger kitchens, living rooms or dedicated spaces like playrooms or home offices. To get the space to be used well and feel open a simple furniture and fitting layout is key. Ground floor rear extensions tend to favour open plan designs which can really open up the space and make it more versatile.
For a first floor rear extension the layout may include options like a master bedroom with an ensuite, making the most of the elevated views of the garden and increased privacy. These designs can make the most of the vertical space and create a peaceful retreat from the more public areas of the house. By reconfiguring with space in mind you can turn a cramped and disjointed home into a smooth and spacious one.
A rear extension is an opportunity to modernise and improve the aesthetics of the house while keeping the original structure intact. By balancing traditional and modern elements you can get a space that is both beautiful and functional. Mixed cladding and clever window styles, including rooflights and bifolding doors can bridge the gap between old and new and get the extension to look modern but integrated.
When integrating the extension with the existing building the choice of materials and finishes is key. For example timber cladding can add warmth and texture to a rear extension and blend it in with the older parts of the house. The positioning of windows and doors will not only affect the external aesthetics of the extension but also how it relates to the rest of the house so you can get a harmonious and seamless result.
Natural light is the foundation of good extension design, transforming spaces and connecting indoors to outdoors. Glazing options like bi-fold doors and strategically placed skylights can bring in loads of light and visually expand the internal space and the extension. A double height glazed atrium can be a focal point and a source of natural light especially in two storey extensions.
Artificial light should complement natural light; spotlights and decorative lighting can add to the ambiance in the evening. A rear extension that gets natural light right can create a seamless transition to the garden and increase the aesthetic and the sense of space in the house. Glazing choices should be considered with privacy and energy efficiency in mind so the rear extension is as comfortable as it is bright.
When considering a rear extension project you need to understand the difference between planning permission and permitted development rights. Permitted development rights is the easier route as it allows certain changes including single storey rear extensions without planning permission. However it’s usually limited to single storey builds.
Planning permission is more restrictive. Getting approval under planning permission can be more difficult especially for builds that go beyond the permitted development parameters like two storey extensions. Planning permission usually requires you to adhere to the stricter criteria set by the local planning authority.
Even with permitted development rights we recommend you apply for a Certificate of Lawfulness. This will ensure the rear extension complies with all local regulations and avoid any potential legal issues. For larger single storey rear extensions you can consider a prior approval application through the neighbour consultation scheme. This involves talking to your neighbours about the proposed build before you start to mitigate any concerns or objections.
Ultimately both approaches aim to balance the homeowner’s need for extra space with the impact on the surrounding community and environment. Whether you go for planning permission or permitted development rights building regulations approval is still mandatory to ensure structural safety and compliance.
Permitted development (PD) rights allows homeowners to make certain changes and extensions to their property without full planning permission. Rear extensions, single and two storey, fall under this category but there are conditions to be met. The rules vary depending on your location so always check with your local planning authority (LPA) before you start.
Under permitted development you can add a single storey rear extension without full planning permission if:
This allows for slightly larger extensions under temporary legislation until May 2026:
If you go for a larger extension under this scheme you’ll need to go through the “Neighbour Consultation Scheme” where your neighbours are notified and the local authority checks for any objections.
For two storey rear extensions permitted development rights are more restricted:
If your extension goes beyond these dimensions or outside of the PD rules you will need to apply for full planning permission. Also local authorities can impose additional restrictions through what’s known as an “Article 4 Direction” which removes or limits permitted development rights in certain areas.
When considering a rear extension to your home it’s important to understand the timelines for different planning applications. For householder planning applications the council will take up to 6 weeks to make a decision from the date of validation. If your rear extension requires planning permission the process will take around 8 weeks for a response from your local planning authority.
For larger single storey rear extensions under permitted development there is a prior approval application process which takes 4-6 weeks. You should pursue a Lawful Development Certificate for your extension to confirm it’s lawful under permitted development rights this takes around 8 weeks.
The whole planning and design process for extensions can take several months 7-15 months. This includes preparation, design stages and getting necessary approvals such as building regulations, party wall agreements and development rights.
Key Application Timelines:
Building regulations are important for rear extensions to ensure all building work is safe, energy efficient and environmentally friendly. Unlike planning permission which deals with the external appearance and overall impact of the extension building regulations cover the technical and structural details. Compliance is mandatory whether you’re building a single storey or double storey rear extension and failing to comply can result in fines, enforcement action or even the need to demolish non compliant structures.
There are two types of building control officers who enforce building regulations: local authority building control officers and approved inspectors from private firms. Both can review your plans, inspect the work as it progresses and issue a completion certificate once the work meets the required standards.
Building regulations ensure your extension is structurally sound and doesn’t compromise the safety of the existing property. This includes:
Fire safety is important especially for double storey extensions. Building regulations will require:
For double storey extensions fire safety measures such as fire rated floors and ceilings and ensuring escape routes are protected from fire for a specified period are required.
Building regulations also cover the energy efficiency of new extensions which must meet current standards for insulation and energy use. These include:
Ventilation is important to maintain indoor air quality and prevent condensation and damp. Building regulations cover:
Natural ventilation in extensions like opening windows must meet the minimum size relative to the room to allow fresh air to circulate.
A key part of any extension project is ensuring drainage systems are designed and installed correctly. Building regulations cover:
You may also need to consider if soakaways or other sustainable drainage systems (SuDS) are required to manage rainwater if you are increasing impermeable surfaces in your garden.
If your extension involves new electrics or plumbing these must comply with building regulations:
Building regulations may require your extension to be accessible for people with disabilities. This could include:
To ensure full compliance it is recommended to engage with building control officers early in the design phase. The process will include:
If your extension is near a boundary you may need a party wall agreement under the Party Wall Act 1996. This is a legal agreement between you and your neighbours to ensure any work to a shared boundary or wall does not damage their property. Building regulations do not cover party wall matters but failure to manage these can lead to disputes or legal action.
Non-compliance can result in:
When planning a rear extension building regulations approval is a key step to ensure your extension is safe, energy efficient and compliant. Working with building control officers, submitting detailed plans and having on-site inspections throughout the build will help you avoid costly mistakes and ensure your project’s success.
When undertaking a rear extension project you need to factor in all the cost variables. Typically these can range from £1,800 to £2,500 per square metre, labour, materials and design complexity will all impact the final cost. A standard single storey rear extension will cost around £38,000 and a double storey extension around £65,000.
The size of the extension also has a big impact on the budget. Small rear extensions of around 15m² will cost between £15,000 and £20,000, medium sized extensions of 25m² will cost between £30,000 and £40,000 and large extensions of 50m² will cost between £50,000 and £60,000. These figures show just how much every extra square metre adds to the cost.
Choosing higher quality materials will add to the cost but will also add to the aesthetic and durability of the extension and potentially increase the value of the property. Professional fees which include services such as architectural design, project management and structural engineering will add another 15% to the total construction cost.
When planning your rear extension budget you need to consider these factors carefully to get a realistic budget for your project.
An extension cost calculator can be a great tool to work out the financial implications of your rear extension. For example laminate worktops will keep costs low at around £30-£40 per m² but granite work surfaces will add to the cost at £400 per m². External doors have a big price range, from £300 for a basic steel door to £1,600 for a luxury patio door.
Smart lighting will add £500 to the cost but will be efficient and save you money in the long run. Heating installations such as a new gas boiler and pipework will cost £2,000-£3,000 and underfloor heating will cost between £60-£100 per m².
Plastering will cost around £25 per m² but painting and decorating will add to this depending on the finishes you choose. Each item on the calculator gives you a better idea of the total cost of your extension.
When it comes to the technical side of your rear extension structural design hiring a structural engineer is often essential to ensure safety and compliance with building regulations. The cost can vary from £400 to £4,000 depending on the complexity of the project. You should expect to pay around £1,500 for the assessment phase of the structural engineering work.
Load bearing walls or the need for steel beams are just two examples where you will need a structural engineer. You need to consider the scale of the structural changes to the existing building and the materials you choose which will both impact the engineer’s fees. Due to the variability of the cost get quotes and consult with professionals to get a accurate quote for your specific requirements.
Planning application costs are an important part of your rear extension journey. In England the standard fee for a householder planning application is £206 which is for single dwellings, full applications and most lawful development certificates. The same fees apply in Wales and Scotland £230 for householder and full planning applications.
Note that applications submitted through the online portal incur an extra service charge of £26.83 plus VAT. For most prior approval applications in England which may be for a rear extension a fee of £96 applies. Knowing these figures is key to your budget for your rear extension.
After your rear extension is built you will need to get a building control certificate with fees averaging around £950 to confirm your new extension meets the building regulations. This is an important part of the overall cost of your extension.
The fee covers the building control officers’ review of plans before construction and their site visits to inspect various works during the build. Compliance with building regulations is mandatory for safety, structural integrity and efficiency to avoid future disputes or legal issues. Knowing these costs will help you to budget accurately.
Rear extensions are a clever way to increase your home’s square footage and living spaces like kitchens and lounges. A modern rear extension will usually be 3-6 meters from the back of the property and will cover the whole width of the house. To flood these new spaces with natural light bifold doors and double height glazed atriums are a growing trend. These will not only light up the inside but also create a seamless transition to the garden outside.
If you’re planning a two storey extension you will need to get building regulations approval. Approval can be obtained through full drawings or a building control notice to ensure your extension meets safety and design standards. If you’re planning a single storey extension you may be able to use permitted development rights to streamline the process as it may not require full planning permission depending on the project.
When thinking about rear extension ideas the design can range from a flat roof which can be minimalist to timber cladding for a natural textured look. Also an external vent pipe can be integrated into the design to hide them from view. Whatever type of extension you choose to make it blend in with the original house and push the design boundaries can result in a functional and beautiful addition to your home.
The beauty of rear extensions is the impact they have on internal space. Not only can they add a lot of extra living space to your home but they can also bring in natural light to the ground floor making it brighter and airier. This extra light can transform an existing space into a more welcoming and open space which is perfect for communal areas like living and dining rooms.
Plus this extra space can add value to your property potentially by 6-20%. The design options for rear extensions are endless from an open plan family space to a secluded home office or a playroom for the kids.
When extending internal space the build process is usually straightforward and may not require full planning permission if the extension adheres to permitted development rules. This simplifies the process and gets you into your new home sooner.
While internal enhancements are part of a rear extension the exterior impact is just as important. Improving the front door and driveway can add value for a future sale. Even small changes to the exterior of the property can have a big impact on the overall look and curb appeal.
For major renovations you should check if planning permission is required especially for listed properties or those in conservation areas. But for minor updates like painting or modernising fences and boundary walls you don’t need planning permission.
You have many options to upgrade your home’s exterior. From simple fixes like repainting surfaces or updating fixtures to more major projects like adding cladding or a new roofing material for long term visual impact. Plus making sure pathways and driveways are well maintained can make a big difference to the first impression of your home.
Choosing the right builder is key to a successful home extension. At Danesfort we deliver quality on time and on budget. We have extensive experience working on home extensions in the London area.
Danesfort ensures all projects comply with planning permissions and building regulations. We offer clear contracts that outline scope, timelines and payment terms so you’re fully informed from start to finish.
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