ARTICLE - Planning a home extension or refurbishment

If you are thinking of starting a refurbishment, extension or new-build project to create an exceptional, creative and inspiring home it is key to allow sufficient time to make sure the project achieve all your aspirations within your programme and budget. Having worked as residential architect in London for over 15 years, Sophie Bates of Sophie Bates Architects shares her experience with you.

Allow enough time

Innovation, inspiring and beautiful homes take time to design. Architects need to present you with designs that creatively interpret the potential of your project to deliver value financially, technically and aesthetically. If you can, allow a minimum of eight months prior to your ideal start-on-site date.


The chart above shows the timeframe in month generally needed for a substantial residential extension and refurbishment. The time frame assumes submitting for pre-application advice to the council at stage 2 and not starting technical design until planning permission has been achieved.


Draw up a project brief

The brief for your projects needs to contain practical and aspirational requirements. Prepare as much as you can prior to meeting your architect. This will allow your architect to develop sketch designs, visualisations and models and inject your requirements into every detail of the design. Have a look at our article on writing a brief

  • What are your key requirements? This could be prescriptive minimum areas and room types or more general types of spaces
  • What doesn’t work about your home as it is? This is often key to understanding how you want to live
  • What is your overall project budget?
  • Are there any time constraints?
  • What is the feel of your home that you are aiming for through the refurbishment or extension? Gather images or projects by starting a scrap book for inspiration e.g. our pinterest board on London extensions. Include interior and exterior inspirational ideas.
  • Clearly separate aspirational wish list items from must haves
  • Gather existing information on the site. This might be any existing drawings or information on previous building work. If there are any restrictions e.g. easements or know services such as a Thames Water sewers – let your architect know.


Find the right architect to work with

Architects are highly skilled individuals who can interpret and realise your ambitions for your house. It is key to find an individual architect or company that you trust, is professional and knowledgeable to guide you through the planning and build process to deliver your home.

  • RECOMMENDATIONS - ask for a recommendation, word of mouth is key. Have a look at our reviews page here.
  • REVIEWS - read reviews online on their service or ask to speak to previous clients.  Have a look for google reviews, Houzz and their website for feedback from past clients. 
  • RIBA - use the RIBA to find you an architect an architect in your area.
  • MEETING - interview a number of architects before making a decision. Make sure that you see their portfolio of previous projects and that they understand your specific needs.  As well as beingtrustworthy, professional and knowledgable  - you need to get on with them well and feel inspired after the meeting.
  • SCOPE OF SERVICE - be clear on the level of involvement you are looking for yourself and for your architect. Is your architect to manage the building contract on site and design the interior finishes of your home?  Scope of service varies between architects so make sure you are comparing like for like.
  • CONTRACT - insist on a written form of contract for services backed by the RIBA standard form of contract to protect all parties.  May sure the level of service and fees are clearly explained.




Budget £

The construction cost is different to the total project cost. Have a clear idea of your maximum overall project budget. Your architect can help you plan your budget. This should include provisions for:

  • CONSTRUCTION COST – this is the cost builder will charge you excluding VAT. Payments are normally monthly under standard RIBA contracts and hold back a percentage of the cost as retention for a fixed period of time to cover any defects once the project is complete. Cost per sqm varies greatly pending on size, location and specification of your project. In London, a high specification project construction cost would be upwards of £2000/sqm
  • PROFESSIONAL FEES – you will need an architect, a Quantity Surveyor to provide an independent, accurate cost assessment prior to submission of planning permission and a structural engineer. For more complex projects you may need a mechanical and electrical engineer. Your architect can guide you on who is needed in the team
  • SITE SURVEYS – e.g. measured building survey, soil survey, drain surveys.  These are needed at the start of a project.  An existing house may also need an asbestos survey.
  • VAT – refurbishments and extensions are subject to VAT. Listed buildings and Change of Use/ number of residential units are at a reduced rate. Make sure you allow for the correct rate
  • STATUTORY FEES – Householder planning applications for extensions and refurbishments currently cost £206, Building Control fees are either through the local council who publish their rates online and range in price pending on construction cost or through an approved inspector
  • PARTY WALL AWARDS – if you are building up to or close to a neighbouring wall or floor you will likely need a Party Wall Award. These can be expensive and you may need to serve notice on more than one neighbour
  • CONTINGENCY – allow for 10% contingency in your budget to cover unknowns - eg. the condition of the existing structure and foundations won't be known until works on site begin.
  • INFLATION - if your cost plan report was done at planning stages but you aren't starting the build for six months to a year or more, allow for a % increase for inflation.

A quoted rule of thumb is to allow at least 1/3 of your budget to cover professional and statutory fees and VAT. Once an architect is appointed make sure they review costs throughout the design process not just for the build cost but the items noted above.

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COPYRIGHT SOPHIE BATES ARCHITECTS. This article is a guide and it not advice. All projects are different.

Good luck with your build!