how much are architects fees for an extension?


How architects set their fees

All architects must calculate the fees to charge on the project, and send this to their client as a written fee proposal. This will take in to account any unique features or requirements of the project, so there is no standard fee. You might find that architects fees are expressed as either:

  • a percentage,
  • a fixed cost,
  • or time charges.

Each method of calculating fees has it’s own advantages and disadvantages. However it is usual for architects fees for a house extension or a new build house to be given as either fixed costs or a percentage.

How much are architects fees for an extension

Architects Fees

usual range of architects fees


Amounts to expect under each method

If your architects fees are based on a percentage of the building cost, then expect anywhere between 12 – 15% for full services from design through to the end of construction.

If your architects fees are a fixed cost then expect a similar amount, i.e. £12,000 – £15,000 on a £100,000 project, however there can be benefits for clients in fixed cost appointments that we will explain in this post.

If a time basis is used then expect this to be in the range of £100 – £150 per hour for a senior architect.

Percentage, Fixed Costs, Time Charges

methods of fee calculation



Fees for each stage can be set as a percentage of the construction cost. This can be useful when the scale of the work is still unknown; as the fees can go up and down with the amount of work involved


Fixed Cost

Fees can be fixed at set amounts for each stage of the project. This is great as you will know exactly what you will need to pay and when; but may not be possible if the scope of the project is not yet clear.


Time Charge

Fees that are charged on a time basis are calculated from records of time spent on the project, and the architect’s agreed hourly rate. This can be combined with a cap on the overall amount at an agreed level.

Many clients value the reassurance of Fixed Fees during the design stages; combined with Percentage Fees during the construction stages so that the fee always accurately reflects the work involved. This often gives the best possible value for money.


Professional Assurance

architects fees and value


Value of Professional Architects Fees

All architects in the UK are required to be registered with the ARB, have trained for a minimum of 7 years and achieved high standards of design, technical ability and professionalism. Although the title of architect is protected by law, the function is not. But when comparing architects fees with those of a technician or designer it is useful to remember that only a professional architect will bring all of the skills and benefits listed below.

  • Professional indemnity insurance
  • Registered and regulated by the ARB
  • Professionally qualified in architecture
  • Planning and technical design knowledge
  • Trained to administer construction contracts
  • Annually assessed continual professional development
  • In addition to the above, some architects such as 2PM are an RIBA Chartered Practice meaning that they achieve the gold standard in professionalism, design and quality assurance.


Architects Fees for a House Extension



How To Agree Architects Fees

So with the information presented above you should just be able to follow these keys steps to agree architects fees that will give you good value and an excellent service.


  • Be as clear as you can about your brief
  • Get architects to submit fee proposals based on the 6 RIBA stages of work
  • Make sure that you are comparing similar standards of architects fee proposals
  • Expect the total fee to be in the region of 8-15 % depending on the complexity of your project
  • Consider agreeing fixed fees for the first few stages, with percentage fees for the construction stages for best value

More Guidance

all posts

We have written a number of posts which provide information and guidanceto anyone considering a project. These include advice on design and planning of new homes, renovations and extensions.



If you have a project you would like to discuss with us then just drop us a line using this form and we will get back to you. Or call us in our London studio on 020 3920 9805.

We will be happy to help and we look forward to hearing from you.



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