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So How Much Does It Cost To Build a Bespoke Extension?

When I first talk to new clients, after kicking around a few design ideas the next question that is inevitably asked is “How much will it cost to build?” It's a bit like asking  “What does it cost to buy a car?”. At the early stage of a project the analogy works quite well and we can discuss whether their aspirations are for a VW Polo or a Bentley Continental. Whilst many clients have never built anything bespoke before, they will certainly have chosen cars and dealt with the multiple options available - the ones that push the final price up!.

A bespoke extension is like buying a beautifully made car. The basic chassis might be similar to many others, but the choices you make about style, quality and longevity will have a big impact on the cost; and you are faced with a surprising number of choices.

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So what are the main drivers of cost?

  1. Location - how easy is it to get to the site, especially with large lorries? The further from a town and the narrower the roads, the more expensive it gets

  2. Trees - tree roots can play havoc with foundations and so if there are trees nearby that can increase groundwork cost

  3. Shape - a complex shape or complex roof geometry costs more because it's trickier to build

  4. External materials - higher quality, low maintenance or longer lasting materials cost more; however in the long run they can be better value for money

  5. Internal finishes - luxurious high quality finishes keep giving every day because of the delight you feel every time you walk into a room. You can be extravagant and stylish as well as functional

  6. Fittings - kitchens. Bathrooms, fitted bookshelves and cupboards merge seamlessly into the design because they just look like they belong

  7. Lighting - my experience is that good lighting can make the difference between good and superb. It can be bold and on show, or discrete and hidden

So what is the likely cost range?

A sensible baseline is £3,600/m2 (including 20% VAT) then add to that for any of the cost drivers above. For that kind of budget you get a simple shape and good quality build with good finishes and fittings and good lighting. Then agree with your Architect what options you want to upgrade and set budgets for those so that you can easily control the cost. Spend wisely and concentrate your upgrade options to those areas that you will really get the most out of in your everyday life.

We can find you a good builder who we can work with to help you achieve your objectives. We've designed and built many beautiful extensions before we have the experience to ensure you get value for money. We use sophisticated and highly evolved 3D design tools to show you how your budget changes as you make choices to arrive at your ultimate design.

How Can We Help?

The quality of the project team is essential. At JHD Architects we have evolved our approach to integrated design and construction management over four decades. So whether your  aspirations are for a VW Polo, a Bentley Continental, or most likely something in between, we can help. We have 40 years experience designing bespoke extensions and we do it well. 

So although we don’t have a standard answer to how much it costs to build a bespoke extension,, instead we will work with you to balance your aspirations with an achievable budget and ensure that you know what you are going to spend, before you’ve spent it. It's your home, it's your budget, you decide on the options.


We make sure your extension has everything you want, at the price you want, with no surprises, so you can enjoy a smooth and enjoyable drive to your dream house destination.

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