House Extensions in London

Increase space and value of your house in London with a side or rear extension 

Extending your house is a great option to gain more space for a new room, to have a larger kitchen or more living space for the family. Any additional space in London is precious, and extending is a cost effective solution to improve your quality of life and increase the value of your property. That is why choosing the right house extension company is crucial for a final result in line with your expectations.

As space is so valuable in London, houseUP will help you optimise your plans. This way you will maximise the design and the space gain for you. Whether you want a larger kitchen, a play room for your children, a cosy living space for TV and video games, houseUP will be on your side to make the best choices for you and your family.

For your home extension, our teams will advise on the best solutions that are cost effective for your specific requirements and needs, with design and build or build services if you already have designs and plans from your chosen architect or designer.



  • Meeting in person: understand what you want to achieve with your home extension in London
  • Understanding the challenges: assess the technical constraints and the budget to find the best and cost effective solutions
  • Viewing the place: see the space and understand your priorities and needs place
  • Discussing your taste and requirements: talk about your needs to focus on what is unique to you
  • Inspecting the building and the area: identify physical and regulation constraints to prevent issues and remove blockers
  • Capturing the unsaid: collect details, expressions, moods to design uniquely for you

A site visit is one of the most important steps for your construction projects. Every house and every person is different. Looking at your property and discussing your vision face to face is the best way to understand your vision, your priorities and your expectations.

Capturing the said and unsaid: what you really want to achieve

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One of our partner architects with experience of house extensions in London in your area sits with you to understand your expectations, explain the cost options and translate your ideas in drawings.

(design and build package only)

  • Translating the vision: transfer on paper your ideas for your home extension in London
  • Overcoming the constraints: create a design that helps you visualise and evaluate
  • Understanding the options: define more than one option to choose the best house extension for your needs and your cost objectives
  • Optimising for the planning: use our planning experience to make the right choice for permitted development, planning permission, building regulations

Getting through all the legal aspects: quickly identify and resolve planning, party wall agreements, requests to council for access, traffic and more It is important to work together to make sure your vision for your renovation in London is transformed in the best design and plans. Priorities and requirements are different for each home extension. Getting them correctly is the secret to success. Sometimes a small inexpensive solution can save a lot of money and make you happier than complex and expensive specifications.

Translating the vision: how you achieve what you want with practical solutions

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One of our partner architects specialised in home renovations in your area produces all the documentation and drawings to get you through all the regulation process

(design and build package only)

  • Liaising with the planning authority: find out details on permitted development, reports and planning requirements in your London council
  • Preparing drawings and plans: submit complete documentation to the planning authorities in your London council
  • Filing the application to approval: submit all the package for the planning process, be it planning permission or permitted development
  • Producing pre-build package:create all the drawings and plans for your home renovations, including building regs, construction drawings and specifications

Managing the design and planning process in London requires a deep understanding of your expectations and your budget requirements. Experience and previous relationship with the local area, council and planning authority are key to maximise the value of your house.

Optimising the planning process: exploit your property’s potential within the planning constraints

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One of our estimation specialists produces an accurate quotation, including a break down of all the details and their cost

  • Defining the construction costs: evaluate the basic construction work for the extension
  • Estimating the options: optimise the choice of structural elements, layout, natural light elements
  • Detailing the specification: define the finishes and identify the suppliers for results that match your expectations
  • Explaining the quote: communicate clearly what is included or not and what are the most cost sensitive details that might impact the final cost
  • Communicating effectively: explain the process and the program for your house extension, set up easy-to-use communication channels, agree on the decision flow

Investing your money for a construction project is an important decision. Getting a quotation that is clear, transparent and comprehensible is the first step to a successful house extension. It’s You That is why understanding the quotation is paramount to make the best decision. A quote that is too high is a scam, a quote that is too low is even more dangerous.

Maximising the value for your money: gain space, light, quality of life and increase the value of your property.

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The construction manager assigned to you organises the construction team, produces the time plan and manages the activities on site to build the extension

  • Creating the program: define a clear program to control the progress and prevent issues
  • Planning the work and executing on site: use experience, best practices, professional competence and the best teams on site
  • Reporting and sharing info: give regular feedback and respond promptly to questions and requests
  • Setting up communication channels: dashboard, live chat, photo and video sharing using the latest tech solutions
  • Making timely decisions: follow a clear process for requests, approvals, last minute changes and all decisions

Works to extend your house can cause disruption in your daily routine. Information sharing and effective communication are as important as the execution of the works. That is why you will have English speaking construction managers on your project and dedicated communication channels to avoid long and confusing email threads.

Delivering up to the expectations: produce top quality results through a hassle- and stress-free process.

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Your construction project manager defines the snagging list, ensures all the tiny details are taken care of and reviews everything with you to get to a successful handover of your house extension

  • Completing the work: finalise all the construction works for you to move in
  • Checking all the details: compile a snagging list to sort out all the small details
  • Wrapping up all the final bits: complete the snagging and sign off the project

The very last few days at the end of your project can feel the hardest sometimes. You can’t wait to complete the works and start your new life and there are always the final details to smooth out. Finalising the last details can feel exhausting, after all the waiting and the disruption during the works, That is why we make sure to be there on your side, for any last minute request, question and fixing. Because seeing you happy is what motivates us everyday.

Taking care of all the final details: complete the snagging, provide all the certifications, warranties and documentation and sign off the project.

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    • Work with an architect with specific experience in your London council
    • Use your London property’s potential in full with the best architects for planning applictions
    • Get planning and building regulations sorted in a smooth hassle-free process
    • Make the most of permitted development rules in your London council
    • (in-house) Optimise your structural design with our in-house engineers and partner architects
  • 02BUILD 
    • Get the best building contractor for your project in your London council
    • Have a structural expert on-site to check that foundations, beams and joists are installed correctly for your home extension
    • Use specialised tradespeople for your project, including electricians, plumbers, carpenters, decorators and more
    • Access exclusive kitchens and porcelain tiles directly from Italy at discounted prices
    • Have an English speaking project manager with specific experience in London
    • Optimise orders, personnel on site, building regs visits and other arrangements
    • Ensure Health and Safety, party wall procedure, planning authorities, neighbours are managed promptly and professionally
    • Follow a clear decision making process to be on top of your home extension in real time
    • Have a project team who knows your area, council and building reg authorities
    • Take control of your construction projects in London
    • Follow progress even from your holidays abroad, through houseUP dashboard
    • Have access to a dedicated channel on houseUP communication platform, for fast trackable decision making and issue management
    • Keep a written record of all the conversations, questions, issues, decisions in one place, avoiding long email thread discussions
    • Understand budget consumption and priorities, remove impediments and blockers in real time

Types of house extensions 

If you are considering how to build an extension to your home, it’s useful to think of all the options you have for the type of property. There are many options for your home extension, depending on your requirements on the size, the size of garden you want to leave untouched and obviously your target budget.

Types of house extensions


It’s an extension at the back of a house, often in the garden. It’s a good option for detached and semi-detached houses. A terraced house extension at the rear of a property is also sometimes feasible.



It uses the narrow space at the side of a house, without using up garden space. It’s a great option for a ground floor extension, to implement a change of character on a ground floor without compromising the back garden area. This is an option for a semi-detached or detached house extension.



It’s the combination of rear house extension and side extension. It can be a very big addition in size to the existing house. It’s feasible for a semi-detached or detached house extension.



It’s an extension of only one storey, like an extension at the rear of a terraced house to make a larger kitchen. It’s an excellent way to extend a terraced house, a semi-detached or detached house. With a single storey extension you can also add a sunroom or a conservatory, or add a play room or a new TV and sofa area to an existing living room.



It extends ground and first floor of a house. It allows to extend a ground room floor, most usually the kitchen, and to create additional space on the floor above, for example enlarging or creating a bedroom or a bathroom. Most commonly it is feasible as an extension of a semi-detached or detached house.



Basement and loft conversions are also types of house extensions. You can check our dedicated pages to basement conversions and loft conversions for more details.

Average cost

Average cost 

The cost for a house extension in London can differ substantially depending on many factors. For example, the area and accessibility of the site is one factor. The nature of the soil can have an impact when new foundations are required. Party wall agreements and the number of involved parties can add to the construction cost.

To be able to budget for your house extension in London, though, it’s important to have an idea of the average costs.

The average cost of a standard house extension in London is between £1,500 and £3,000 per sqm, excluding finishes like windows, flooring, sanitaryware etc. At this price, the added value to your property is about double per square metre. For instance, in 2017 in the cheapest London borough the average property value was calculated as £4,000 per sqm.

Planning and permitted development requirements


Under permitted development, you have the right to extend your house without the need of planning permission.

For home extensions, there are some basic constraints for permitted development:

  1. Area: the area of side and rear extensions must be less than 50% of the total free area around the house
  2. Appearance: the exterior appearance must blend in with the existing house and the neighbourhood
  3. Width: the width of side extensions must be less than 50% of the width of the existing house
  4. Length: the max length of rear extensions is 3m for terraced or semi-detached houses, up to 4m for detached houses
  5. Height: the height of single storey extensions must be less than 4m. For two-storey extensions, the height must not exceed the height of the existing house eaves. If the distance to the boundary is less than 2m, only single-story extensions are allowed under permitted development.
  6. Balconies and terraces: they are never allowed within permitted development rights
  7. Loft and basement conversions: they have specific permitted development requirements. You can learn more on our loft conversion and basement conversion pages.

Rules are stricter in designated areas, where the above conditions might not be sufficient to have the right to permitted development.


Planning permission rules vary a lot depending on the council. As general rules, conservation, green belt, archeological and other designated areas have stricter requirements on alterations and building works that are allowed. It is important that you choose professionals who have experience in your council to support your planning permission application.


Questions and answers

Collected questions that we often hear from you

  • Can I live at the property during the refurbishment? 

    We always recommend that you arrange for alternative accommodation during the project.

    Some of our clients choose to live at the property during the work, and, of course, we make that possible. However, please be advised that this arrangement comes with a significant increases in stress, cost and duration of the project.

  • Do I need planning permission for my refurbishment? 

    You won’t need planning permission for most refurbishment projects. If you are not changing the external appearance of your flat or your house, you won’t need planning permission. In many cases, you can make a loft conversion or a rear/side extension within permitted development rights. You can find all the details on which type of extensions are allowed under permitted development here.

    However, if you are planning to refurbish a listed building, you may need permission.

  • How long will my refurbishment take? 

    As per the duration of a project, it cannot be estimated without the full details. If you want to plan ahead, for alternative accommodation for example, we recommend at least:

    For smaller flat refurbishment, approximately 4 to 6 months. For house refurbishment, approximately 6 – 8 months These estimations relate to straightforward refurbishments like loft conversions or rear and side extensions. More complex work like basement excavations can only be estimated with more details, especially if access to the property is a consideration. Composition of the soil etc are also important factors.

  • How much will my refurbishment cost? 

    Every good building company will tell you that it is not possible to estimate the cost of refurbishment for a flat or a house before all the details have been defined. But we understand that it is important to have a reference figure before embarking in the process for budgeting purposes.

    We suggest a conservative estimate of £1,750 per square metre as the absolute minimum, and an average of between £2,000 and £3,500 per square metre.

    However, it’s important to keep in mind that there are details that can impact the cost significantly, the most costly being basement excavations or extensions of existing lower ground spaces; inclusion of very large or high spec glazing; very high energy performance materials.

    Additionally, some finishes can increase costs significantly, like paint, tiles or flooring, especially if the surfaces are very large,.

    In general, kitchens can be installed from as low as a few thousand pounds to hundreds of thousands, too.

  • I am buying a property, can you help me estimate how much the refurbishment would cost? 

    When you buy a new property, it is very likely that you’ll plan for a refurbishment. You can find some very good deals on the market, where you can buy a property for a good price when it needs some work done.

    By offering an estimation on work to be done, we can help you make the right decision and offer the right price for the potential property.

  • I have all the drawings ready with my architect, can you do the building works for me? 

    We certainly can! We work with the best architects in London through a tender process, for clients that choose to have the designs for their refurbishment made by an independent architect.

    We can provide quotes in our own very detailed format or in your architect’s preferred format.

  • I want to do everything with one company, can you do design and refurbishment for me? 

    Yes we can. We partner with the best London architects to create designs that suit you and your needs. We will match you with architects who have specific experience in your area, share your vision and style for your refurbishment project.

    Doing the design and build with us gives you a view and control of the projected costs of your refurbishment from the very first day. You will be able to make well-informed choices for your design while understanding the cost implications and opting for the best solution for your investment.

    Check out our Design & Build page for more information.

  • What works make the biggest difference in the final cost of my refurbishment project? 

    Typically excavation to extend or create a basement under an existing property is one of the most expensive types of work in construction. The cost of finishes is another big factor in the final cost of a flat or house refurbishment.

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