How Long Does It Actually Take to Build an Extension?

Build an Extension

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Build an Extension

Extending your home is a popular option for adding living space. An extension is a great way to add more space, create a larger living area, and increase the overall value of your home. Many homeowners, however, are unaware that constructing an extension is a complex and time-consuming process that necessitates careful planning, design, and construction.

In this article, we’ll go over the factors that can affect the timeline for building an extension and provide a rough estimate of how long an extension takes. We’ll also go over the steps involved in planning an extension and offer advice on how to manage your expectations throughout the construction process.

Planning an Extension

Before you begin construction on an extension or loft conversion, you should have a detailed plan in place. This plan should cover everything from hiring an architect to obtaining development permission, developing a detailed design plan, and locating a builder. The following are the major steps in planning an extension:

Rear Extension, Side Extension or Something Else?

Firstly, you need to decide what type of extension you would like to add to your existing property. This can have a big impact on timescales and how you go about planning your project. For example, loft conversions are usually more straightforward than a full-blown renovation project or large extension.

Finding an Architect

An architect can assist you in creating a detailed design plan for your extension. They can also advise you on local building regulations and assist you in obtaining any development permission.

Creating a Detailed Design Plan

After you’ve obtained planning permission, you’ll need to create a detailed design plan for your extension. This plan should include everything from the layout and size of the extension to the materials and finishes. You should also consider extension costs within your plan and whether you can afford what you want to build.

Obtaining Planning Permission From Your Local Planning Authority & Building Regulations Signoff

Most extensions in the UK require planning permission from the local authority. This process can take several weeks or months, depending on the complexity of your project and local planning regulations.

Finding a Builder & Construction

Finding a reputable builder is critical to the success of your extension project. A good builder will provide a detailed quote, a clear timeline, and a professional outcome.

How Long Does It Take to Build an Extension?

Now that you know the key steps involved in planning an extension, let’s explore how long an extension takes to build. Below this section, we have included a list of timescales to help summarise our points below.


Depending on the complexity of the work, the timescale of the design process can vary. There are also several factors to consider such as:

  • Type of extension
  • Design preferences and complexity
  • The time it takes for you to respond to your designers
  • Structural calculations or work required

Planning Permission

The time it takes to obtain planning permits depends on the local authority and the complexity of your project. Local authorities (those who grant planning permission) aim to conclude the planning approval within 8 weeks. But in reality, this can take longer. In more recent times, we’ve seen applications take around 6 months!

Structural Engineer Or Other Consultants

If your extension involves changes to the existing house, you may need a structural engineer to calculate the required steelwork or structural work. This process can add 2-4 weeks to the project timeline.

Site Surveys

A site survey or measured survey to gather existing drawings or other surveys such as asbestos, existing structure, daylight, traffic, and acoustic may be required to ensure that your extension is built to the correct specifications. This process can take several days or weeks, depending on the size and complexity of the project.

Building Regulations

All extension projects must comply with building regulations. This process involves obtaining approval from a building control officer and can add 1-3 weeks to the project timeline.

Permitted Development Rights

In some cases, homeowners may be able to build a single-storey extension or two-storey extension without a planning permit, under permitted development. However, there are strict guidelines that must be followed.

Party Wall Agreement

If your extension involves building work on a party wall (shared with your neighbour), you must obtain a party wall agreement. This process can vary a lot, depending on whether your neighbour agrees to appoint your chosen surveyor or their own or whether or not your neighbour refuses the work and asks for their own conditions. Party walls are a sensitive subject and should be tackled by the correct professionals.

Tender Process

If you’re working with a builder, the tender process can add around 8 weeks to the project timeline. This process involves obtaining quotes from several builders, analysing the quotes, selecting the best option based on price, quality, and experience, and finally, negotiating and signing a contract.


Depending on the work involved, construction timescales need to be considered. This can be the actual construction work itself, as well as lead-in times for materials and specialist subcontractors.

Before beginning the home extension project, it is critical to obtain any necessary permits or certificates from the local planning authority. If the new extension requires work on a party wall, a party wall agreement must be obtained. It’s also critical to ensure that the extension complies with building codes and regulations.

There are several types of home extensions to consider, including single-story, double-story, and rear extensions. Depending on the size and scope of the project, it may be possible to use permitted development rights, which can speed up the process and reduce home extensions costs.

The process of building a new extension can vary depending on the project’s complexity and the availability of materials and labour. Hiring a project manager can help keep the project on track and ensure that everything is completed on time and within budget. It is also critical to have an accurate estimate and tender documents in place before beginning the project.

Overall, constructing an extension can be a complex process requiring careful planning and execution. Working with local builders who are familiar with the area and have experience with extension projects can help ensure a professional finish. Understanding the various stages involved and potential challenges that may arise allows you to create a detailed schedule and rough guide to help ensure a successful project.

Possible Challenges


Building an extension is a difficult and time-consuming process. Here are some examples of potential project challenges:

  • Consultant Delays: Delays in design are a risk. Sometimes consultants are overworked or hit an unexpected issue.
  • Builder Delays: Because of the volatility of the construction industry, start dates with your builder may be delayed. This could be due to labour or material shortages or delays on other projects.
  • Demolition: During the demolition of the existing property, unexpected structural issues can arise, adding time and home extension costs to the project.
  • Structure and Groundwork: A lot of risk is in the ground, and when pouring new foundations, you may uncover issues such as nearby trees or Thames’ Sewers.
  • Roofing: High winds and heavy rain can cause the roofing stage of the project to be delayed.
  • Electrical and plumbing issues can add time and money to the electrical and plumbing stages of a project. Often coordination here is the key issue.
  • Finishing Work: Delays in obtaining materials or labour can add time and money to the project’s finishing work stage. Snagging is also a contentious topic that can take weeks or months to resolve.

Timeline for Building an Extension

Building an extension can be a difficult and time-consuming task. While the exact timeline will vary depending on the project’s specifics, the following are general estimates for how long each stage may take, for a basic extension and refurbishment project:

  • Planning and design: 6-12 weeks
  • Obtaining necessary permissions and certificates (e.g. planning permit, building regulations, lawful development certificate, party wall awards): 8-16 weeks
  • Tender Period: 6-8 weeks
  • Site preparation, scaffold erection, and foundation work: 2-6 weeks
  • Structure and framing, including roof/roof tiles and external walls: 4-10 weeks
  • Internal carpentry and plastering (1st fix): 6-10 weeks
  • Finishings/Fittings/Kitchens/Sanitary Ware (2nd fix): 8-12 weeks
  • Electrical and plumbing installation: 2-6 weeks
  • Commissioning and Handover: 5 weeks

Some of these works run alongside each other, which means the actual duration is slightly shorter. Below are some outline guides for durations of construction projects:

  • Basic Extension – Design/Approvals/Tender: 4-8 months. Construction: 16 weeks / 4 months.
  • Large Extension – Design/Approvals/Tender: 4-8 months. Construction: 18 weeks / 4.5 months.
  • Extension and Internal Refurbishment: 4-8 months. Construction: 22 weeks / 4.5 months.

Several Factors Can Speed Up or Slow Down the Process, Including:

  • The complexity of the design: More complex designs may require more time to plan and execute.
  • Availability of materials and labor: If materials or labour are in short supply, this can delay the project.
  • Unforeseen issues: Unexpected setbacks such as inclement weather, structural problems, or supply chain issues can cause delays.

To Keep The Project on Track and Minimize Delays, It’s Important To:

  • Regularly communicate with contractors and subcontractors to ensure everyone is on the same page.
  • Create a detailed schedule that outlines each stage of the project and when it should be completed.
  • Build in contingencies for unexpected setbacks.
  • Keep a close eye on the budget and make adjustments as necessary.

Ultimately, building an extension is a significant investment of time and money, but with careful planning and execution, it can be a worthwhile way to add living space and value to your home.


What Are Some Of The Biggest Factors Impacting The Timeline For Building an Extension?

  • The size and complexity of the extension
  • The location of the project
  • The need for planning permission or other approvals
  • The availability of materials and labour
  • Unforeseen issues that arise during the construction process

How Important Is Careful Planning and Design In Reducing The Overall Build Time?

  • Careful planning and design can significantly reduce the overall build time by minimizing errors and delays in the construction process
  • A well-planned project will have detailed plans drawn and specifications, which can help to streamline the construction process and reduce the risk of errors or misunderstandings

What Are Some Of The Most Challenging Stages Of Building an Extension, and How can Homeowners and Contractors Work Together To Overcome Them?

  • Some of the most challenging stages of building an extension include obtaining necessary approvals and permits and delays with builders
  • Homeowners and contractors can work together to overcome these challenges by maintaining open communication, staying organized and on schedule, and being prepared to adapt to unexpected changes

How Much Variability Is There In The Timeline For Building an Extension, Depending On Factors Like The Size, Complexity, and Location Of The Project?

  • There is a significant amount of variability in the timeline for building an extension, as each project is unique and will have its own set of challenges and requirements
  • Factors like the size, complexity, and location of the project can all impact the timeline, as well as the availability of labour and materials and any unforeseen issues that arise during the construction process

What Are Some Of The Key Differences Between Building a General Extension and a Kitchen Extension In Terms Of Scope and Timeline?

  • A kitchen extension is typically a smaller project than a general extension and may require different permits or approvals
  • A kitchen space extension will also typically involve the relocation of appliances and the installation of new plumbing and electrical systems, which can add complexity and time to the project timeline

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How Long Does It Actually Take to Build an Extension?