Skip to main content
Architect Tips

How Long Does An Average Extension Take

How Long Does An Average Extension Take

Many factors need to be considered when calculating the timeframe for building extensions, which means that those time frames can vary widely. At the bottom end of the scale, a standard single storey extension can take around six months from beginning to end. If the extension is more complex, or things move slowly for reasons beyond your control, things can take a lot longer.

Building an extension can be exciting. However, the entire process must be managed well for a stress-free project, especially if you are doing this for the first time. Therefore, engaging an architect to support you so that you have a professional looking out for your interests is vital in the long run.

Engaging with a professional will ensure that all of your design needs are met whilst ensuring that every detail has not been overlooked. This outlay in the first instance can not only make sure that you have a space that you absolutely love, but it is future proofed and takes into account how life, and families, can change and grow with time.

Step One: Figuring Out The Goal

To begin with, you’ll need to think about two aspects. The first is what you want to accomplish by adding an extension to your property, and the second is to set a budget to define what you can afford.

The two most common reasons for building an extension are:

  1. Increase living space
  2. Create additional value in your home

The cost of any extension will depend on the size of the space you are creating, the materials used, and other associated work that may also need to be undertaken. To give you an idea, most home extensions can cost upwards of £3,300 (m2).

For example, if you wanted to build a 30m2 single-storey extension, you could be looking at a cost starting at around £120,000 for a single storey extension (this is for a shell finish without decoration and fixtures), plus VAT at 20%. Also, remember that this isn’t a concrete figure because there are still many variables to consider in each design and build.

Once you have a clearer picture of what you wish to achieve with your extension, an architect can help you cost your plan accurately and show you many ways to save money.

To get the most out of your budget on something like this, we recommend speaking to one of our team here at Formed Architects. We have extensive experience in maximising the value of a home and would be happy to talk to you to see what would be possible for you.

Step Two: The Design Process

After creating your goals and budgets, the second stage is to hire an architect to first schematically develop a proposal based on your brief and project requirements prior to developing this into a more finalised proposal going forward.

As architects, we can provide a lot more than technical drawings. There’s a vast difference between providing just drawings and a well-considered design service that takes you through each stage whilst keeping your brief at the forefront of design and protecting your interests throughout.

Architects are trained to think creatively about solutions and understand all legal aspects you might encounter when undertaking an extension build, including how to add to your property if you live in a conservation area for example.

Working with an architect that suits your particular needs, style and budget is important. Doing so will deliver a more tailored design for your extension at a cost you can be comfortable with. It’s worth remembering that architects work for you as opposed to working directly with builders and interior designers who could potentially look out more for their budgets.

Step Three: Planning Permission

The questions we get asked quite often are, Do I need planning permission, and how long does it take to get planning permission?

Understanding what exactly is possible and within the guidance is crucial. Even permitted development (where planning permission is not typically required) has complex rules. To avoid experiencing difficulties from the outset, it’s helpful to speak to an architect who can advise on what routes are available to you and what would be involved in making a planning application.

If planning permission is not required, we suggest that a Certificate of Lawfulness be obtained under Permitted Development Rights, as this will confirm that what you are proposing complies fully with its rules, policies and guidelines.

Planning permission timeframes will vary case by case. Most applications can usually be determined successfully in 8 weeks. The time limits can be extended to at least 13 weeks if they are unusually large or complex. Due to the ongoing cases, planning officers request additional time on statutory timeframes.

At Formed, we seek to follow up with the assigned planning officer after the initial consultation period has ended, typically three weeks from validation. We will then strive to work with them to achieve a positive and practical outcome.

This action allows the officer to ask for any changes before the decision date and make design amendments where needed to help ensure that your application is approved.

Step Four: Working With Your Neighbours

A party wall agreement must be obtained if your extension building work is near or on a party wall. The party wall represents a shared boundary separating two houses and is usual for terraced and semi-detached houses.

As the homeowner, you need to give two months’ notice in writing for building works which affect a party wall or structure. One month’s notice will be required if you are planning excavations or building on the line of junction. We strongly recommend you consult your architect for the best advice for your circumstances to ensure compliance is met under the party wall act.

Step Five: Finding the Right Builder

While getting recommendations from friends and family is one approach, you’ll need to seek out accredited building firms with the correct insurance and experience for the type of work you need. They also need to deliver your project for the right price and with who you feel you can trust and get along.

At Formed, we have a network of trusted traders that you can utilise for your using a compiled tender package for a builder to provide an accurate cost for works, to ensure everything has been allowed for in their price prior to works commencing on site. By getting the right building team for the job, you will ensure the result is as true to your original dream vision as possible.

Step Six: The Building

You have a complete set of drawings in which your builder has provided a price that you are happy with to create your new home extension, but in what order will everything happen? There are always exceptions to the rules; however, in general, the majority of house extension building projects follow a similar process:

  1. Site Establishment
  2. Demolition/Groundworks/Drainage
  3. Build structure/Roofing/External Finishes
  4. Internal Renovation and Remodelling
  5. Services, Internal Fit Out and Finishes

If we’re managing your extension project, we can arrange for a return visit around three months after the project has finished to see how things are getting on and to discuss any latent issues after completion. Now your builders have completed your home extension, sit back, and relax, as your extension is yours to enjoy.

Are you ready to build your extension?

The above processes should only be taken as guidelines. Your process could be shorter or longer, depending on what you’re trying to achieve.

While the timeframe may sound longer than you’d like, these steps are necessary to get an extension that works for you and your family.

To make your extension building process as smooth as possible, we recommended working with an experienced architect. They will know everything there is to know about planning permission, dealing with local authorities, building regulations, and how to make your extension as functional and beautiful as possible, among other things.

If you need help with your extension, you can contact us here at Formed Architects by calling 020 3601 3480 or emailing