One of the most difficult questions I get asked is how much will it cost to design my home extension?  I have helped many homeowners design and extend their family homes over the last 10 years, from their initial ideas through to the completed construction, this is still a very difficult question.

I have found that every client, every project and every budget is different and therefore it is important to work in a way that works for you.  Whether you want a full service from start to finish or you’d like to choose just a few of my services, I am happy to help you as little or as much as you would like.  

Because every building project is different in size and complexity, the fairest way I have found to offer my professional services is through an hourly rate of £85 per hour (VAT not applicable).  

Other costs associated with a typical extension project which you need to consider may include:

  • Measured survey fees
  • Planning application fees
  • Building control application fees
  • Structural engineer’s design fees
  • Build over agreement fees (when building close to or over a shared drain)
  • Party wall agreement fees (when building up to or close to your boundary)


Common questions

What disbursement’s do you charge?
Usual disbursements are charged for travel, printing and purchasing ordnance survey plans. 

Why do you charge an hourly rate?
I have found this to be the fairest way of charging for my services, so you only pay for time spent on your project.

What is your lead-in time?
Fortunately, I am always very busy.  As a rough guide, I would need around 3 months from your instruction to start looking at your project.  

How long does the process take?
Working up your extension design, applying for planning permission and building control approval can take months or years! As a guide, I would allow between 6 months and a year to get the necessary designs and statutory approvals in place.   

Why do you charge to undertake the initial visit?

If you are seriously considering an extension and you want clear and impartial professional advice from a Chartered Building Surveyor, then paying for an initial visit/consultation will provide you with meaningful answers and a strategy to take your project forward. 

Why are you more expensive than some others in the area?
I don’t see my services as expensive but provide incredible value. I price my services to undertake the project diligently and to ensure the survey and design processes are not rushed. You will be investing a large sum of money into your extension and it is important that you invest in these early stages to ensure your project gets off to the best start and designed to achieve the final outcome you want. The number one cause of budget and programme over-runs is rushing through the design process.  A well thought out design will add value through the whole process and reduce your stress levels when you come to build your extension. An out of control project is expensive and very stressful.  I am a Chartered Builder Surveyor, meaning I am regulated by the Royal Institute of Chartered Surveyors.  I hold professional indemnity insurance and public liability insurance. I also use the latest CAD software.  Although you may pay a little more in my professional fees, it is an investment to get your extension project off to the right start, and hopefully, be money worth spent in getting the design of your extension just right for you. 

How many hours would it take for you to design my extension?
This will be dependent on whether you know exactly what you would like and the complexity of the design, and ease of going through planning and building control.  Here is an example of a few home extension design projects recently undertaken and the number of hours taken to design, prepare and submit both planning and building control applications, to give you a guide:

Single Storey Extension on Modern House:  16-20 hours
Large Single Storey Rear Extension with Internal Alterations/New Kitchen Layout on Modern House: 40-50 hours
Two Storey Extension on Modern House:  60 hours
Two Storey Side Extension and Single Storey Rear Extension on Modern House:  60-100 hours
Single Storey Extension to Period Property with Flemish Bond Design Fulling Designed:  90 hours
Large Two Storey Extension on Modern House or Two Storey Extension to Period Property:  110 hours


Feel free to CONTACT me and I’d be happy to run through all of the above in greater detail.




Extension Sketch Scheme

“From Start to finish Jonathan Durndell was very professional in every aspect of his work . From the 1st appointment the communication was excellent and never had to chase him for anything which I think is invaluable when working to deadlines. The costs were exactly as he quoted which I found reasonable and he never rushed me at any of our appointments. I have used this company three times now and dealt with Jonathan on all occasions and found him very knowledgeable. He has come up with some great ideas which I have used numerous times.  The drawings they produced were very accurate and detailed in which my tradesman all commented on.”

Mr Neil Wrist, Oxfordshire