Rubislaw Den zinc extension, Aberdeen.
Unfortunately, that’s a bit like asking how much a car costs – there is no definitive answer. A Fiesta and Bentley will both get you from A to B, but one is priced at £15k and the other £150k.
The same principle applies to building an extension. There are so many variables that impact cost, that it’s impossible to create a blueprint which will apply to every project.
We can, however, give a realistic idea of an extension’s average cost per square metre. We’ll take a closer look at that later. But firstly, and most importantly, let’s consider the factors which influence an extension’s cost.
Size, Shape and Height
The biggest impact on price is how the space will be used. For example, a kitchen or bathroom extension will cost far more than a small office or playroom extension. Typically, the larger you go with size, shape and storey height, the more you can expect to pay.
Type of Construction
The construction method of your extension will also influence cost. A simple timber frame extension will be more economical than a complex steel frame extension. Similarly, the type of building materials used in the external finish – timber cladding, glass, metal, stonework – will all vary in price.
Windows and Doors
High-end, triple glazing or bi-fold doors will cost more than standard windows and doors. The materials of window and doors will also affect price. UPVC is more affordable than aluminium or timber.
Finishes and specification
The finish of your extension will have a big impact on price. Think of this as you would the star rating of a hotel. A standard-spec finish (3 stars) with off-the-shelf laminate flooring, basic MDF skirting boards/windowsills and standard lighting fixtures are budget friendly.
High-spec luxurious finishes (5 stars), such as solid wooden flooring, natural stone tiles and custom-built cabinetry will add a unique look to your extension, but also increase the cost.
Kitchen and Bathrooms
For a bathroom, you’ll need to add about £5,000 to the cost of building your extension’s shell. However, this can vary widely depending on the bathroom suite and finishes you choose.
A kitchen will cost more than a bathroom, adding on around £10,000 for a low to mid-range kitchen.
Demolition and Waste Removal
Will an existing extension or structure need to be demolished before your new extension can be built? This will need to be factored into the cost, along with skip hire and removing waste from the site. If asbestos is present, a specialist contractor will be required to remove this safely.
The groundworks, such as digging a foundation, improving drainage, or underpinning will all play into your final cost. If you’re looking to build on an area of uneven terrain, expect your prices to be higher than if you were building on something existing and flat.
Other Costs to Consider
As you can see, there are several influences on the cost of an extension. Therefore, it makes sense to discuss your budget with your builder from the very start. The Coldwells team can guide you on what type, size and spec of extension you can expect for your budget.
A lot of focus is often placed on build rates to calculate the cost of an extension. Build rates are referred to in pounds per square metre (£/m2) with m2 being the total internal floor area of your proposed extension.
Whilst we consider these rates below, we would always advise consulting a professional builder and investing in the initial design of your extension to ensure your budget and project expectations match.
From our own recent building data, and that of our architect partners based in Aberdeen and Aberdeenshire, we know realistic build rates are currently:
£2500 + VAT
£3000 + VAT
*These figures are as of Spring 2022 and are subject to change based on market forces and inflation.
What does this cost include?
These costs are for building the shell of the extension only and don’t include the price of any fixtures and fittings. Nor does it include the cost of kitchens and bathrooms as these can vary widely in price. A kitchen can cost £10,000 (budget range) or £50,000 (high end & bespoke) – it really comes down to your budget.
As every project is unique, the prices in the table above are a guide only and exact figures can’t be attained without accurate architect and engineer’s drawings. The Coldwells team can assist you with this.
Building an extension is time consuming, costly and complex and so you will need a team of professionals familiar with dealing with these challenges. If you find a builder who insists they can deliver a ground floor extension, including a full house refurbishment with an associated square metre rate of £1800 + VAT – there will be a reason for this, and it will not be positive for your project.
In our experience, such rates are unrealistic and often end up with a long list of “extras” which should have been included in the initial costing and which cause stress to both the client and their budget.
If you’re in the process of planning your house extension and could benefit from some real-world professional advice about budget, logistics, timing or any other elements of renovations or new custom builds, then please get in touch on 01975 223011 or email@example.com to schedule a complimentary planning session.
As professional builders, we are a much wider resource than just construction.
Editors note: This article was last updated March 16, 2022