Skip to content
Home / News / How Long Does It Take to Build an Extension?


How Long Does It Take to Build an Extension?


Architectural Design


House Extensions

How Long Does It Take to Build an Extension?


Adding an extension to your home is a popular option for many who are looking to expand their existing living space, or create new rooms for the changing needs of the household, be that the addition of a functional space such as an office or playroom, or the expansion of an existing space to increase the overall value of the property. 

Whilst there are many benefits to extending your property, an often overlooked variable is the time it takes for an extension to be built, as well as the roadmap for its delivery, which, depending on its size and specification, can be complex and diverse. Other factors to consider are what implication local planning regulations may have on the approval and timeframe of delivery, as well as those further outside of our control, such as the weather. As a result, forming a definitive deadline for an extension isn’t straightforward.

The purpose of this guide is to provide a view of the different stages involved in building an extension, as well as their standard associated timeframes. This will help to establish a realistic timeframe for delivery so that plans can be developed in line with expectations, and which minimise the stress and disruption that the build of an extension can bring.

Factors Affecting the Duration of Extension Projects

There are a number of factors that can influence the delivery timeframe of your extension, and understanding the implication of each of these in isolation is crucial in establishing a timeline of delivery for your project. Let’s start by looking at some of the common variables:

1. Size and Type of Extension

Extensions that are complex and highly detailed contribute to construction costs and it’s duration, as opposed to those which are uncomplicated, small-scaled and straightforward. The addition of a single room can be completed relatively quickly compared to a double-storey wrap-around extension that includes the addition of two new bedrooms, a bathroom, and a utility. Whilst this may seem obvious, factors such as significant remodelling, quality of the interior, and materials used are often overlooked and can add several weeks to months onto the lifetime of a project.

2. Planning Permission and Regulations

Planning permission can significantly affect timelines due to its sometimes long and complicated approval process, which can vary depending on the location of the property and the types of work being undertaken., Another key element of planning is the process for appeal, should your original application fail, which can be long and convoluted in itself.

3. Design Phase

The design phase of an architectural build is a crucial component of any project, and for similar reasons as those listed in the size and type of extension, can add considerable length to the delivery of a project with high levels of complexity and detail. Whilst this doesn’t mean that you should strive for architectural designs that are basic, it’s important to strike a balance between enhancing the property whilst ensuring that it’s completion satisfies its required functionality.

4. Weather Conditions

Although weather conditions sit external to the control of the overall project, adverse conditions such as heavy rain, snow, and strong winds can limit the ability of contractors and builders to undertake their role. Whilst different times of year can be considered where weather conditions are more favourable, there are no guarantees when it comes to mother nature!

Phases of Building an Extension

Extensions are typically built in several stages which can be broken down into distinct phases to establish a timeline for delivery. Let’s look at a general timeline for the design and construction elements of an extension, and how long each of these phases may take.

1. Concept and Design

Concept and design drawings are produced by an architect, who will work with you to establish your needs and the requirements of the property so that a viable picture of the design can be created. Factors often considered in the design phase are potential planning restrictions, the style of the existing property and how this will influence the expansion of the property, and the desired function that the extension will serve – be that additional living space or as a means to increase the value of the property. Depending on these factors and your requirements, this stage can take two to six weeks

2. Planning Permission

Planning permission is a key aspect of any extension project, and the submission of an application can take anywhere from eight to thirteen weeks. This doesn’t take into account scenarios where planning applications fail the approval process, in which a planning appeal can be submitted. In some scenarios, this can add anywhere between four to six weeks to the planning application process.

3. Building Regulations

Before any construction works begin, your extension will need to comply with building regulations. This includes submitting detailed plans to a building control body, which can usually take five to six weeks.

4. Contract Administration

Having the right team in place to build your extension is essential to the success of any project. Building contracts should have visibility of the designs, and have knowledge of the specifications of the build and the detail required to ensure the project is delivered in line with the designs. 

5. Construction Begins

Designs established, planning approved, building regulations satisfied, and the relevant contractors in place, the building work can finally begin. Depending on the project’s size, scale, and complexity,, the construction of an extension can last anywhere from eight weeks to six months or more.

6. Final Inspection

Final inspection is when the building control body confirms the extension has been built to plan and in line with building regulations. Whilst this process is usually quick and only lasts a few days, it’s important to plan for this within the wider lifecycle of the project, as well as any unforeseen circumstances that may lead to the extension not passing its final inspection.

Do We Need to Move Out When Building an Extension?

A common question that homeowners ask is whether they need to move out of their current property during the construction period of the extension, and if so, how long for. There are several factors that come into play that may influence your decision:

1. Size and Location of the Extension

Small extensions that are located in a part of your house that’s easy to separate from your living area are less intrusive throughout the construction phase than a larger build that spans more than one floor or aspect of the property. The construction periods for these types of extensions can be impractical from the standpoint of noise, dust, or loss of privacy.

2. Comfort Level

It’s not unreasonable to not want to live on a building site, where there is constant noise and disruption – especially for those that work from home. Temporary accommodation throughout the larger elements of your construction may provide you with the privacy and tranquillity you need to complete a day’s work, or simply maintain a normal family life.

3. Project Timeline

Some extension timelines are lengthy, particularly those that are detailed and expansive or require significant remodelling. Consider the length of time that you may be required to live alongside the construction of your extension, and decide if this will work for you.

4. Safety Regulations

Some circumstances may require you to vacate the property, or if you share your property with young children or the elderly, you may wish to remove any risk posed to them during the construction of your home.

Ultimately, and similar to many of the factors discussed throughout this guide, it comes down to personal circumstances, preference, and your desired outcome. Whatever your choice, it’s important that you discuss the feasibility and implications of staying at your property throughout the construction process with your architect or contract administrator so that they can help you decide the best course of action.

Time Estimates for Different Types of Extensions

Extension projects can range from the simple addition of a single room to building a second floor with multiple living spaces. The complexity and size of the project can drastically impact the time required for a project to reach its conclusion, and whilst the below estimates have been provided as a guide, some estimates may vary depending on the nature of the build.

1. Single-Story Extension

Assuming that planning permission is granted without any delays, the entire process for a single-story extension – from initial design stages to the final build – will likely take anywhere from 12 to 16 weeks. This includes time for construction which typically runs between eight to ten weeks.

2. Double-Story Extension

A two-story extension significantly increases the project’s complexity and scale. As a result, you should typically allow approximately 20 to 24 weeks for the complete process. This includes approximately 14 to 16 weeks for the construction phase itself.

3. Loft Conversion

A loft conversion is typically less intrusive than other extensions, as most of the work is confined to the existing loft space. However, it still involves a significant amount of work. Depending on its complexity, a typical loft conversion may span between eight to 12 weeks.

4. Conservatory or Orangery

A conservatory or orangery can be a less complex extension project, especially under permitted development rights. Conservatories typically take between ten to 12 weeks to complete from start to finish, while orangeries usually take a bit longer, approximately 12 to 14 weeks.

These are approximate figures, and timescales will ultimately depend on several factors, including obtaining planning consent, the complexity of the design, seasonal impacts, and the efficiency of your contractors. Therefore, always be prepared for the timeline to vary to some extent.


Building an extension is a significant project, which needs thoughtful planning and a good understanding of the various stages involved. The completion timeline of an extension can vary greatly, influenced by several factors such as the type and complexity of the extension, the planning regulations involved, the impact of adverse weather conditions, and the availability of your chosen contractors. By understanding the influencing factors, you can plan appropriately and prepare for potential delays so that a smoother, less stressful construction process takes shape.

Should the need arise to vacate your property during the construction of your extension, consider the best option for temporary accommodation that meets your comfort, budget, and proximity needs. Whatever your circumstances, always remember that enhancing your home is an adventure. Approach it realistically, patiently, and positively, and you’ll undoubtedly reap the rewards.

Share on your socials...

Facebook X LinkedIn

Let’s create something Amazing

We believe that architecture is not just about buildings, it’s about building relationships grounded in trust, transparency, and shared vision.

With over two decades of comprehensive experience in the architecture sector, our service offering is broad, meticulous, and finely tuned.

Get started today...

It all starts here, tell us a bit about your project and one of our expert architects will get in touch to discuss your idea in more detail.