This is the big question
How much will it cost? As Architects we get asked this all the time, sometimes on the phone having never even viewed the property! There is a reason this topic is at the forefront of everyone’s mind when thinking about extending your home; ground floor extensions can be one of the biggest personal investments you’ll ever make. Like any home improvement project, getting it wrong can be a disaster but getting it right can be an opportunity to transform your home and change the way you live!
Designing your extension
Before I attempt to answer the question, it’s important to understand that cost is dependent on design, but what does ‘design’ really mean? Design is a far-reaching word for physical and intellectual material that describes how something is created.
We know that buildings are complex. They are all completely unique, with different constraints, problems and opportunities, and this is why it’s vitally important to surround yourself with the right people from day one.
Each house has it’s own footprint so to really understand your property and develop an extension that blends seamlessly into your current design you’ll need a team that are committed and able to add detail to the design in the right places. It’s the detail that will make your property shine, and protect your vision for a bespoke ground-floor extension when the big bucks are being spent.

Do I need an Architect for a ground floor extension?
To ensure your project runs smoothly from start to finish its best to make the most of a range of professionals. An Architect is a great place to start, (especially one specialising in ground floor extensions!) but there are a lot of options; you can find a draftsperson to draw something up, maybe you even know someone who could do this for you?
While there are online architects who will do this remotely, my advice would be to find a local Architect (please note the capital ‘A’ and the protected title – this matters!). This is because, as a local architecture firm they will value your project, and have time for you and your numerous questions throughout the journey.
Remember there are a lot of facets to ground floor extensions so it’s important to ask for reviews and compare service offerings rather than focussing on cost alone!
Not all Architects offer the same service so be particular about what you want. While some draftsmen will charge just a few hundred pounds, there is a reason that Architects charge up to 10% of the total project cost – years of experience and a commitment to diligent support throughout the project do come at a premium but will pay dividends in the long term!
Which professionals are required to build an extension?
For a ground floor extension you’ll almost certainly need a structural engineer. Take a recommendation if you get one. A bad consultant who is slow or incompetent can derail the whole process and leave everyone blaming each other.
Quantity Surveyors are often overlook for homeowner projects – don’t! For a few thousand pounds you will get valuable advice from the concept stage all the way through to a bill of quantities.
There are other things to pay for along the way such as planning application fees and building control fees – but these are nominal in the grand scheme of most ground floor extensions so don’t worry unduly about these.
The build process for a ground floor extension
Then there’s the build! Cue suspenseful music, this is the finale, the climax of the process and where all the pieces will fall into place OR where it will go terribly wrong.
So how do you figure out where you stand and what’s really important?
It can be confusing and there are so many differing opinions. In my opinion, the answer is in the detail. Detail. Detail. Detail. Take control of the process and make sure that you pay for a set of documents that account for EVERYTHING and that the site has been triple checked by the builder and that you have a full set of costs prepared (impartially) that are agreed too. By operating this way the only risks are the unknowns, not the ignored.
You wont be able to do this on your own. Your home is your most valuable asset so don’t scrimp! Sometimes it can even be worth scaling back your ideas or taking the time to find more funds for a dream build, otherwise you can end up dealing with unwarranted pain and stress.
Working with an experienced Architect will help you to understand what you can afford and offer realistic advice instead of simply telling you what you want to hear until its too late! Get a good Architect and trust them, its an exciting journey and one that could make you a huge return on your investment!
So, how much does it cost, I’ll just answer the question. Here you go..
Approximate cost of a ground floor extension
For a single storey extension budget for £3500/m2 for the build and account for 15% on top of that for professional fees and about 20-30% again for interior finishes/nice glazing and fancy stuff.
There I said it.
If you’re interested in a detailed quote for your extension please don’t hesitate to get in touch with one of our friendly team members – we’re always happy to help!