House Extensions; The Ultimate Guide To Planning Your Home Extension

An image of a bathroom in a new house extension

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Are you looking to add more space and value to your home?

Expanding your living space and increasing the value of your property has become a popular solution for homeowners. House extensions have become the go-to option for those seeking extra space. However, with so many factors affecting the cost of an extension, it’s understandable to wonder “How much will it cost to extend my house?”

This comprehensive guide to planning a house extension will cover all the crucial aspects you need to consider, from understanding the average cost of an extension to the timeline involved and common mistakes to avoid. In this guide, we will provide you with the necessary information and planning guidelines to make informed decisions about your house extension. From getting an extension quote to understanding building costs, this guide will cover it all. Whether you’re just starting to plan your extension or are ready to take action, read on to find out how much you can expect to spend on a house extension.

Extending Your House: Designing the Project

Expanding your house can be a complex process, but with proper preparation, you can increase your living space and improve your property’s value. One of the most critical steps is the design phase, where you bring your vision to life and decide on the appearance, functionality, and feel of the extension. In this guide, we will explore the steps involved in approaching the design stage of your house extension project.

Conduct Research:

Start by exploring various house design resources, such as online websites, social media, design magazines, books, and professional resources like architects, contractors, and interior designers. Gather inspiration from different sources to determine your design style, which will help you establish your preferences and narrow down your options.

Take Advantage of Home Design Resources:

Utilize the abundance of information accessible online and in print. Online resources like home design websites and blogs can provide inspiration and information, while social media can connect you with other homeowners who have undergone similar projects. Print resources like house design magazines and books are also great sources of inspiration and information. Professional resources like architects, contractors, and interior designers can provide practical advice and guidance on extending your home.

Establish Your Design Style:

Take into account your personal preferences and the style of your current house. Determine the look and feel of your extension, whether you prefer a modern, traditional, or eclectic design, and if you want your extension to blend in with your current house or make a statement.

Collect Inspiration:

After determining your design style, gather inspiration and create a vision board to keep track of your ideas. This can be a physical or online board that will provide a visual representation of your vision and help you communicate it with others involved in the project.

Compare Costs and Materials:

When planning your house extension, it’s crucial to compare costs and materials. Consider the materials you want to use and their impact on your budget. Decide which materials and finishes are within your budget and which ones may need to be adjusted.

Understand Building Codes and Regulations:

Familiarize yourself with the building codes and regulations in your area before beginning the project. This will make sure your extension meets local standards and that you understand what is and isn’t allowed.

Seek Professional Assistance:

Hiring a professional, like an architect or interior designer, can help bring your vision to life and navigate the building codes and regulations. They can also ensure that your extension meets local standards.

Additionally, you may require planning permission and comply with the permitted development rules, which can vary based on your local planning authority. You may also need to follow building regulations, obtain a lawful development certificate, and consider other limitations, such as the Party Wall Act.

The cost of extending your house will depend on various factors, such as the size of the extension, the materials used, and your location. It is recommended to consult with a planning consultant before applying for planning permission to build an extension.

Builder London

Types of House Extension?

House Extension Types

Extending your existing house is a great way to increase its value and create additional space. Many homeowners choose to build a house extension to have a larger kitchen, extra room, or more living space. However, before extending your property, it’s important to understand the various types of house extensions and the factors that influence the extension cost.

Single Storey Rear Extension

A single storey extension is an economical solution that involves adding new living space to the back or side of your property. This type of extension is a popular choice and can cost anywhere between £50,000 and £150,000, depending on the size, equipment, and location of the suggested extension.

Two Storey Extension

A two storey extension is a more extensive option that involves adding an additional floor to your property. This type of extension is suitable for those who want to create additional space on the upper level of their home. The cost of a two storey extension is estimated between £75,000 and £200,000, based on the size, tools, and location of the extension.

Wrap-Around Extension

A wrap-around extension involves adding an extension to both the rear and side of your property, giving it a wrap-around effect. This type of extension is ideal for homeowners who want to have a larger kitchen or living space, and the cost is estimated between £50,000 and £200,000, depending on the size, tools, and location of the suggested extension.

Orangery Extension

An orangery extension is a more unique and premium option that involves adding a partially enclosed, glazed structure to your home. This type of extension creates a bright and spacious area for entertainment or relaxation, and the cost is estimated between £30,000 and £70,000.

Permitted Development Rules and Regulations

Before building any type of extension, it’s crucial to understand the permitted development rules and regulations. Depending on the location and size of your suggested extension, you may require planning permission from your local planning authority. Permitted development rights allow homeowners to extend their property without applying for planning permission as long as they comply with the permitted development rules.

Building Regulations Approval

In addition to the permitted development rules, it’s also important to consider the building regulations when building an extension. The building regulations approval is necessary to ensure the safety and well-being of the occupants and the structure of the building.

Other Considerations

When extending your property, you should also consider other limitations, such as the party wall act and planning rules, as well as the conservation area in which your property is located. It’s advisable to consult with a planning consultant to ensure that your suggested extension complies with all necessary regulations and requirements.

In conclusion, extending your house is a long process that requires careful planning and consideration of many factors. The extensionprice can vary based on the type of extension, the location, and the equipment used. It’s best to get a free quote from a professional builder to determine the cost of your suggested extension and ensure that your project is completed within budget.

Is an Architect Necessary for Your House Extension?

When you are planning to extend your house, the question of whether or not you need an architect may arise. Although it is not a requirement, there are many advantages to working with an architect. These experts have experience in creating other buildings that are both functional and visually appealing while also ensuring compliance with all relevant regulations and standards.

An architect can assist you in making the most of your available space and customizing your extension to fit your specific needs. For instance, if you are looking to add extra space to your property, the architect can design an extension that optimizes your space and creates a functional and aesthetically pleasing room.

In addition to offering design services, architects can also guide you through the technical aspects of your side extensions or front extensions project. They can advise you on the party wall act, other building regulations, and fire safety and ensure that your suggested extension meets all regulations and standards.

Whether you’re planning a single-storey extension or two-storey side or front extensions, an architect can help you navigate the planning process and obtain the necessary approvals from the local planning authority. Although it may involve an upfront investment, working with an architect can ultimately save you time and money by ensuring that your extensions is completed to a high standard.

Overall, while you may not necessarily need an architect for your house extension, working with one can provide many benefits and ensure that your extension project is completed to a high standard. Whether you are looking to build a single-storey extension or two, storey extension, or a front or rear extension, there are many aspects to consider and planning rules to follow. To get the most out of your extension and ensure that you have a functional, safe, and aesthetically pleasing new space, it is advisable to work with a professional.

If you’re looking for an architect, we can probably help. Check out our architectural services.

Architectural Design palette

Other Consultants, You Might Need When Planning a House Extension

When extending a house, there are various consultants that you may need to consider beyond just an architect. These professionals can help ensure that your extension is completed in a safe, legal and high-standard manner.

Structural Engineer:

If your house extension is large or complex, you may require the services of a structural engineer. This professional can evaluate the load-bearing capacity of your existing house and ensure that the extension is structurally sound. They can also help in designing the foundation and other structural components such as steel beams to support the added space.

Building Control:

Building control is responsible for overseeing building regulations and standards. When planning an extension, you will need to apply for building control approval, and a building control surveyor will need to inspect the work during and after construction. This professional can ensure that your extension meets all the relevant building regulations and standards, making it safe for use.

Party Wall Surveyor:

If your extension is close to, or on, a shared boundary with a neighboring property, you may need to appoint a party wall surveyor. This professional can help understand the party wall agreement, which outlines the rights and responsibilities of both parties involved. They can also help resolve any disputes that may arise and ensure that the work is carried out in accordance with the agreement.

Project Manager:

If your extension is large or complex, you may benefit from the services of a project manager. This professional can coordinate all aspects of the plan, including design, procurement and construction. They can help keep the plan on schedule and within budget and resolve any issues that may arise.

The consultants you may need when extending a house vary based on the size and complexity of your plan. It is important to assess your needs and find the right professionals to help achieve your goals.

What do I need to know about the party wall act?

When you are thinking about extending your house, it’s crucial to be aware of the Party Wall Act and how it could impact your plan. The Act governs the relationship between owners of adjoining properties when work is done on a shared wall or boundary.

If your extension involves work that will touch a shared wall or boundary, such as excavating near it or constructing an addition that will join a neighbouring property, you will need to serve a Party Wall Notice to your neighbors. This notice outlines the suggested extension and provides your neighbours with the chance to either object or agree to the works.

In some situations, you may also need to appoint a Party Wall Surveyor to serve as an impartial expert and manage the works. This surveyor will make sure that the work meets the standards of the Party Wall Act and resolve any conflicts that may arise between you and your neighbors.

It’s important to be familiar with the Party Wall Act and take the necessary steps to abide by it when planning your house extension in London. Not following the Act can result in legal action and slow down your project.

If you are uncertain about your obligations under the Party Wall Act, it is recommended to seek the advice of a surveyor who has experience in handling party wall matters. They can assist you in navigating the process and guarantee that your extension plan is completed smoothly and without any issues.

Party Wall Act

What about building control and the local planning authority?

Building control is a crucial aspect when considering a house extension. It is a regulatory system that ensures all new building work, including extensions, complies with certain standards for health and safety, energy efficiency, and accessibility.

In general, building control approval is mandatory for any alteration work on an existing property that involves changing the structure or creating extra room space, such as a house extension.

The purpose of building control is to guarantee that your extension adheres to all relevant building regulations and standards. It is an impartial examination of the extension plans and construction to ensure that the work is secure, accessible, and meets minimum energy efficiency standards.

When planning a house extension, it is essential to contact your local building control authority to get an understanding of the requirements and steps necessary to obtain building control approval. They will provide you with comprehensive information on the building control method, including what documentation and drawings you need to submit and any fees involved.

By working with a local building control authority, you can ensure that your extension is built to a high standard and meets all necessary regulations, protecting your investment and ensuring that your new space is safe and functional for years to come.

Planning Permission in London: Understanding the Process of Building Extensions

Building a house extension in London can be a complex and time-consuming procedure, but it can also be a rewarding one. By adding extra space to your home or improving its value, you can create a better living environment for you and your family. Here is a step-by-step guide to help you successfully build an extension in London:

Obtain a lawful development certificate:

Before having planning application permission, you may need to obtain a lawful development certificate from your local council. This certificate confirms that your proposed extension meets the planning rules and regulations in your area.

Hire a planning consultant:

When applying for planning permission, it is recommended to seek the help of a planning consultant. A consultant can guide you through the procedure, help you understand the planning extension rules, and advise you on the best way to build your extension.

Apply for planning permission:

Once you have obtained a development certificate, you can apply for planning application permission. This procedure involves several factors, including the design and size of your extension, the materials you plan to use, and the impact of your side or rear extensions on the surrounding environment.

Comply with the party wall act

When building a side or rearextension, you need to comply with the party wall act, which governs the rights and responsibilities of property owners who are building works that affect an adjacent property.

Consider fire safety requirements and roof pitch:

In addition to the party wall act, you also need to take into account the fire hazard requirements and the roof pitch of your side or rear extension, as well as the height of the eaves.

Follow height restrictions

In London, you can build an extension that is no more than four metres in height and no more than two storeys in height. Front extensions are generally not allowed, but side or rear extensions can be extended up to two metres and one storey.

Obtain additional planning permission for large extensions

If you want to build an extension that is more than four metres in height or more than one storey, you will need to comply with additional planning application rules and restrictions. You will also need to take into account the height and design of other buildings in the area, as well as the development rights of your property.

Comply with building regulations

Throughout the building process, you need to ensure that your extension is compliant with the planning extension rules and building regulations of your local council.

Planning permission approved

Planning Permission and Permitted Development Rights

Before you begin building an extension, it’s essential to check the planning permission and permitted development rights with your local planning authority. If your proposed extension falls within the permitted development rights, you may not need to apply for planning permission. However, you may still need to comply with building regulations and get building regulations approval from your local authority.

Can my neighbour stop or object to my extension being built under Permitted Development rights? 

Permitted Development rights are a set of planning regulations that allow homeowners to make specific alterations and extensions to their existing houses without obtaining planning permission. Even if you are constructing your extension within the limits of your Permitted Development rights, your neighbour still retains the right to object to it.

Typically, objections from neighbours stem from concerns such as loss of light or privacy, the impact on their property or view, or worries about the effect on the value of their property.

If your neighbour objects to your extension, they can raise a complaint with the local planning authority. The local authority will then review the objections and make a decision on whether to approve the extension.

It’s important to consider your neighbor’s objections and make an effort to resolve any disputes prior to starting building work. Effective communication and understanding can help avoid objections and make sure that your extension plan runs smoothly.

If you are unable to reach a resolution with your neighbor, you may need to seek legal advice or appoint a mediator to help settle the matter. In some cases, it may be necessary to modify your plans to address your neighbor’s concerns.

While Permitted Development rules offer some flexibility for homeowners to extend their properties, it’s essential to understand that neighbors can still object and raise disputes. Good communication and mutual understanding can help prevent objections and ensure that your extension project runs smoothly.

How long will it take to build my extension?

When considering an extension on a house, it’s crucial to have a clear understanding of the timeline involved in the process to ensure a smooth completion. The timeline for a house extension plan consists of several key stages, from the initial design phase to the final construction phase.


The design phase of your suggested extension can take anywhere from a few weeks to several months, depending on the size and complexity of the plan. During this time, you’ll work with an architect or designer to develop your ideas and create detailed plans.

Planning Permission:

After completing the design phase, you’ll need to apply for planning permission if required. This process can take anywhere from several weeks to several months, and will depend on the complexity of your proposal and the speed of your local planning authority. It’s essential to check the permitted development rights and rules, as well as the building regulations and any other limitations that may apply to your property.


Once you have obtained planning permission, the next step is to seek quotes from contractors for the construction work. This stage can take several weeks to several months, depending on the size and scope of the work.


The construction phase is the most time-consuming and can take several months to several years, depending on the size and complexity of the extension. This stage typically involves the physical extension of your home and can take anywhere from several months to over a year to complete.

Overall, extending your house is a lenghty process that requires careful planning and consideration of many aspect. Whether you’re looking to extend your existing house to provide more room or add a new space, it’s important to comply with the development rights and rules, obtain the necessary permits and approvals, and budget for the extension price. Contact a consultant for a free quote and to find out more about the procedure of building an extension.

Gantt chart showing anticipated programme

What is the cost of an extension on a house?

When it comes to adding an extension to an existing house, it’s important to determine your budget before starting the planning process. This will help you make informed decisions about the type of extension you can afford, including the tools and features you want to include. To get a better understanding of the extension price, it’s crucial to consider various factors that can affect the price, such as size, location, and type of equipment used.

Cost of Planning and Building

The cost of planning and building a side extensions or front extensions can vary greatly. This can include the cost of obtaining a quote, the cost of design and planning services, equipments, construction, permits, and fees, and the cost of hiring consultants such as a structural engineer, building control, and party wall surveyor. To get a better understanding of the extension cost, it’s recommended to ask local builders for ball-park figures and gather multiple quotes from different contractors.

Cheapest Type of House Extension

While you may be tempted to opt for the cheapest type of house extension, it’s important to keep in mind that the cheapest option may not always be the best. Instead, consider your space, functionality, and aesthetic needs and work within your budget to find the best solution.

Single Storey Rear Extension

A single storey rear extension is a popular and cost-effective way to add extra room space to your existing house. However, there are extension rules and building regulations you need to comply with, such as eaves height, roof pitch, and fire hazard requirements.

Two Storey Extension

If you need more room, a two storey extension may be the solution. However, there are planning rules to consider, such as the height of the extension, the distance from the original house, and the distance from other buildings.

Side and Front Extensions

Side extensions and front extensions can also add extra space to your home, but there may be more restrictions to consider, such as the party wall act, building regulations, and the lawfulness of the development.

Long Process and Other Restrictions

Building an extension can be a long process, and there may be other limitations to consider, such as the conservation area, planning application, and other development rights. It’s important to work with a consultant and get a development certificate to ensure that your extension complies with the extension planning rules and regulations.

Get a Free Quote for Your House Extension

There are many factors to consider when extending your house, and the cost can vary greatly. To get a better understanding of the extension cost, it’s recommended to get a free quote from local builders. This can give you a rough estimate of the costs involved and help you set a budget for your extension plan.

Cost of an extension

Planning an extension; find the best builder

When planning a house extension, there are several key considerations that must be taken into account to ensure a successful outcome. One of the first things to consider is to:

Get recommendations

Always try to get recommendations from friends, family, and other trusted sources. This can help you find the best builder for your needs, as well as give you a sense of what to expect from the procedure.

Research, research, research! 

Another important aspect of planning a house extension is to do extensive research.This includes reading online reviews, checking builder portfolios, and exploring design and building websites. This will give you a good understanding of what different builders have to offer, as well as what types of designs and materials they specialize in.

Obtain 2-3 quotations

When it comes to obtaining quotations, it is important to obtain 2-3 quotes from different builders. However, it is important to remember that the cheapest quote is not always the best option. It is important to thoroughly check quotations and to ensure that you understand what is included, and what is not included, in the final cost.

Finally, it is important to remember that the builder can only work from the information that you provide to them. It is essential to be clear and concise about your design needs, budget constraints, and other important details, so that the builder can provide the most accurate quote and timeline for your project.

Common Mistakes To Avoid When Palnning A House Extension

  1. Rushing the design procedure: It is important to take your time in the design phase of your house extension plan. Rushing through this procedure can result in a poorly thought out design that may not meet your needs or fit your budget. It is recommended to take the time to thoroughly consider your options and make informed decisions about the design of your extension.
  2. Not checking quotations properly: When requesting quotes from contractors, it is important to make sure you have provided them with a detailed description of the work to be done. Quotes that seem too low may not include important details or may cut corners on materials or workmanship. It is important to thoroughly review each quote and compare apples to apples to ensure you are getting the best value for your money.
  3. Micro-managing your build team: While it is natural to want to have control over your house extension plan it is important to trust your contractors and give them the space to do their job. Over-managing the build team can lead to delays and increased stress for everyone involved. Instead, communicate your needs clearly and allow the professionals to do what they do best.
  4. Project managing your own extension: Unless you have experience in construction and project management, it is usually not recommended to manage your own home extension project. This can result in misunderstandings, mistakes, and ultimately, a project that is not completed to your satisfaction. It is better to leave the project management to a professional who has the skills and experience to ensure the project is completed on time and within budget.

These are some of the common mistakes that people make when planning house extensions. Avoiding these mistakes can help ensure that your extension project goes smoothly and results in a space that meets your needs and exceeds your expectations.

Conclusion: Planning a Home Extension?

Building a home extension can be a daunting task, but with the right planning it can be an immensely rewarding experience. Following these simple steps will help to ensure that your project stays on track and within budget. If you’re thinking about extending your home, why not sign up today and tell us about your dream renovation? Our team of experts are here to help make your vision a reality.

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House Extensions; The Ultimate Guide To Planning Your Home Extension