Taking on a double storey extensions project in 2023: everything you need to know

UK Home Improvement

Taking On A Double Storey Extensions Project In 2023: Everything You Need To Know

Planning an extension project for your property can be an exciting and daunting task, especially if it’s your first time renovating a property. With any type of extension renovation project, it is wise to know the ins and outs of taking on the particular extension at hand. In this article, we will discuss the key factors you need to be aware of when it comes to taking on a double storey extension in 2023. 

A Good Investment To Make

A double storey extension is a good investment to make for any type of property. Whether you are a property developer or a homeowner, a double storey extension is a cost-effective solution to gain maximum floor space without compromising on your garden space. With this type of extension, you don’t run the risk of your property becoming too bottom heavy which is often an issue with a lot of single storey extension renovations.

Also, the excavation and the roofing costs will not differ compared to a single storey which makes the cost per square metre for a double storey extension considerably lower compared to a single storey extension. 

Average Costs Of  A Double Storey Extension

When considering a two storey extension, the costs for these types of renovation projects will differ and be dependent on:

  • Location
  • The complexity of the design
  • site access
  • soil composition
  • Size of the extension in square metres
  • type and shape of the roof and the roof material that will be used
  • Features such as windows, doors and flooring

In 2023, on average, you can expect to pay around £2,000 to £2,500 per sqm for a basic two storey extension build. As mentioned, the price will differ across the UK, such as London locations where the average price psm can range from £3,000 to £3,500. On top of this average cost are the sometimes overlooked professional fees that go into the project which include:

  • Architect design fees
  • Structural engineer fees
  • Building and site survey
  • Planning permission and applications
  • Building regulation applications
  • Party wall agreement fees
  • Lawful Development Certificate 
  • Kitchen  and bathroom installations

So with these added fees, you are looking at a price of around £60,000. Of course, this will also be dependent on how much of the project you take on yourself. 

Permitted Development 

For some two storey renovation projects, planning permission won’t be required as long as the project falls in line with the permitted development guidelines. Permitted development guidelines include:

  • Maximum Height – The eaves and pitch heights cannot be higher than the height of those that are already existing on the property. If the building is within two metres of a boundary, then the eaves’ maxim height will be lowered to 3m
  • Footprint – Permitted development regulations allow for extensions to exceed 3 metres above from the original height of the house. The extension must also be more than 7 metres from the rear boundary
  • Materials – Materials that are used within the extension should be similar to the existing materials 
  • Location – If the two story extension plan is for the side or front of the building then the plan will not fall under permitted development

If your proposed double storey extension does not meet the requirements that are outlined under permitted development then your other option is to put in for planning permission. If you find yourself having to opt for planning permission then hire a freelance architect or a design and building company to get the best chance of your planning being granted.

How Long Does A Double Storey Extension Take?

As with any type of extension project, the time it takes to complete a double storey extension can vary when taking into account the planning and legal work and the actual construction work that needs to be carried out. 

Estimated Planning Time

On average you can expect the planning stage of a double storey extensions project to last anywhere between 8 weeks to 12 weeks.

Estimated Preparation Time

Depending on the difficulty involved within the agreement, a party wall agreement could take just one or two weeks or could last up until a few months. Preparation such as structural design work and technical drawings have an estimated time frame of around 6 weeks.

Estimated Construction Time

An average estimation of the duration of a double storey extension will be around 16 weeks, which of course will be dependent on the size of the extension. Our time estimates are outlined below:

  • Foundational work – 1 – 3 weeks
  • RSJ Beams and other structural columns installation – 1 week.
  • Plastering – 2 weeks
  • Roof installation – 2 weeks
  • Ground flooring and secondary flooring – 1 week
  • External walls – 2 weeks
  • Plumbing and electrics – 1 week
  • Flooring, windows and doors installations – 2 weeks
  • Painting and decoration work – 1 week


If you’re planning an extension, whether single or double storey you’ll want to get you ducks in a row before you commit to it. Knowing the ins and outs of it by reading this article will give you a better understand of the different stages and timelines as well as costs involved to put you in a better position to making the decision.


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