Extension Design Costs

Ever wondered what your extension design costs might be? Of course, there are many factors that influence the fees involved and ultimately, each project is assessed individually for its own merits, surroundings and specific restrictions, but below are examples of average costs incurred that you can use as a guideline.

Following an initial consultation with Jon and an estimate of costs being produced for your project, we will organise a meeting for our architect to attend site to speak with you and ensure they are able to design your project to meet your requirements. All prices are inclusive of VAT.

Projects that fall within Permitted Development rather than a Full Plans Application can usually be undertaken with some basic plans submitted as a Building Notice and a supporting Certificate of Lawfulness to validate the work as Permitted Development. There is a considerable cost saving for the design of PD projects so consider this approach if you can.

Intial Visit – Architect ……… £No-Charge

Visit the site, discuss Client’s requirements, assess the property and surroundings for Planning and Building Regulations and any drainage implications.

Professional Home Extension Specialist
Measured Survey ……… £360 – £450

Undertake a measured survey of the existing house, boundary and drains (with a colleague if necessary).

Prepare Drawings of Existing ……… £750

To prepare floor plans, sections and elevations as existing for the planning application.

Do I need an architect?
Develop Concepts & Planning Application ……… £1200 – £1800

Prepare floor plans, sections and elevations as proposed to reflect the brief and requirements. Once the proposals have been developed to Client satisfaction, prepare a supporting planning statement to accompany a planning application. Submit a planning application to the Local Planning Authority (electronically through the Planning Portal).

A Planning Application fee payable to the Council of circa £206 plus a Planning Portal submission fee of £20 is also in addition to the above fee.

Planning permission for extensions
Structural Engineers Calculations ……… £250 per element

Your project may not have any structural elements that require a formal design and calculation to support it so this may not be applicable. On the other hand, there may be a structural knock through, large glazed openings such as roof lanterns or bifold doors. On complicated sites, a soil analysis and foundation design may need to be undertaken.

Extension Design Costs
Building Regulation Drawings ……… £1200 – £1800

Developing the design details, preparing proposed detail drawings, sections and elevations required to support a Building Regulations application.

The Building Regulations fees are added to this and are dependant on the size and scope of the project. These fees are either paid to the Councils Building Regulations department or to an independent company if you use those instead.

Sewer Build Over Agreements……… £550 – £750 plus £450 to Anglian Water

An application would need to be submitted (at Building Regulations stage) to Anglian Water to carry out a “build over”. Anglian Water charges an initial fee £450.00 for a Build-over Agreement. To support an application, Anglian Water requires some or all of the following information:

  • Location plan (in colours specific to Anglian Water)
  • Site layout, detailing site boundary (marked in pink), road, existing sewers, live/new assets (marked in blue), dead or abandoned assets (marked in red), drains, watercourses and site contours.
  • Longitudinal sections of live/new assets (sewers), suitably scaled drawings, showing levels, proposed cover and invert levels, pipe material, pipe strength, pipe diameters, bedding
    classification and details.
  • Construction details, detailing manholes and manhole schedules. To include a declaration on the drawings that all work will comply with the current Sewers for Adoption guide and any Anglian Water amendments to that document.
  • Copy of the Planning Approval.
  • Copy of the Anglian Water Data Asset plan
  • Evidence of title to all the land through which sewers will be constructed.

If the sewer needs to be diverted then the above would still apply and costs are similar.
In addition, Anglian Water would require a CCTV survey of the drains to support the application. This costs in the region of £280 per survey.

For more information about sewers adopted by Anglian Water, click here.

Party Wall Agreements……… £0.00 – £1500

Where the works form new foundations within 3m – 6m parallel to adjoining neighbours properties or requires structural support on a Party Wall between properties, the Party Wall Act will apply. This can be addressed with a simple template letter but if you end up in dispute with your neighbour then a Wall Surveyor appointed by (or on behalf of) the Client will need to be used to organise a resolution.

For more information about the Party Wall Act, click here.