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Building a House Extension - What Do I Need?

Updated: Nov 22, 2022

Draw Plans are London based Architectural Designers & Consultants that specialise in adding space and value. We provide Design & Building Plans for any type of House Extension or Loft Conversion within 7/10 days. Prices Start from £795 Plus Vat for a Single Storey House Extension.

Here is a summary of Architectural Services that you may need to build your own extension.


01: Extension Design Plans

Adding an extension to your home is a huge investment so it is crucial that you use an experienced and gifted architectural designer to create plans for your extension.

At Draw Plans, our Design Plans Package for a Single Storey Extension includes onsite client consultation, measurement survey, consultation with local planning, research, preparation of draft sketches, further consultation with client, preparation of design plans for your extension and layout changes to your existing floor plan.

Draw Plans Cost From £ 795 Plus Vat


02: Planning Application Submission / Single Storey Extension

If you are building an extension you may also require a Full Planning Application, a Prior Approval Application or a Certificate of Lawful Development.

To make a planning application on behalf of the client to the local planning authority, prepare planning application plans, including any necessary supporting documents such as Design & Access Statement, CIL Levy Q&A, Biodiversity Statement etc, submit application and liaise with the planning authority to ensure validation of the application.

Liaise with the planning authority throughout the planning application process. Work with the appointed planning officer, negotiate and amend/tweak plans if required. Keep client informed and generally work towards a positive outcome.

Draw Plans Cost From £ 295 Plus Vat (Additionally, you will have to pay the Planning Authority cost of the application.)



3D Architectural Visualisation services are a great aid to the design process because they allow you to get a real feel of what your home is going to look like before you commit to the build.

If you are worried about how your extension or loft conversion is going to look like on the outside or how the new interior layouts will work out then 3D visuals will be an enormous help.

Draw Plans provide a full range of 3D Architectural Visualisation Services including Exterior 3D Views, Interior 3D Views, 360 Deg Internals and CGI Animation 3D Video Walkthrough.

Prices Start with £195 Plus Vat for 4 Exterior Views or 3 Interior Views.


04: Building Regulations Drawings / Single Storey Extension

To build your extension you will also require Building Control Approval and a full set of Building Drawings.

To create a full set of Building Regulations Drawings and Detailed Sections suitable for Building Control Approval. Work also includes for liaising with the local Building Control office or a client appointed Approved Inspector and making adjustements or tweaking the plans as necessary during the build process.

Draw Plans Cost From £ 995 Plus Vat


05: Structural Design & Calculations

If you are making structural alterations to your property you will most likely require a Structural Design Plan and Structural Calculations for your project. It is not possible to provide a quote for Structural Design & Calculations until the Design Plans have been completed.

Draw Plans will be happy to arrange free quotes for Structural Calcs.


06: Party Wall Agreements

If you are building an extension within 3 metres of a neighbouring property you will most likley require a Party Wall Agreement with your neighbour.

Most extension projects require Party Wall Agreements. Depending on the layout you may need a PWA with more than one neighbour. You should also note that the neighbours are entitled to instruct their own surveyor and if they do, you would be expected to pay their costs also.

Draw Plans will be happy to advise and or deal with party wall issues for your project. If you know your neighbours we can also advise you how best to proceed and provide you with the necessary notice documents free of charge.

Draw Plans PWA Agreement / Award £850 Plus Vat Per Dwelling


07: SAP Calculations

Sap Calculations may be required if your extension design includes excessive amount of glass. Under the building regs you are allowed up to 25% of the floor area to be used for glazing to the walls and ceiling.

If you exceed 25% you may have to have SAP Calculations carried out which will allow you to use more glass in return for upgrading existing elements within the original part of the house.

Draw Plans SAP Calc Costs From £ 350 Plus Vat


08: Specification & Schedule of Works / OPTIONAL

Having a costed Specification & Schedule of works done for your project is a great way of finding out at the early stages what the project is going to cost.

The schedule is also a big help when it comes to getting quotes as you can provide builders with an un-costed schedule and plans which means everyone is pricing the exact same job.

It is also a great negotiation tool because you will know if you are being overcharged on any of the works.

Draw Plans Cost From £ 295 Plus Vat


09: Full Project Management Services / OPTIONAL

Draw Plans provide Full Project Management Service for house extensions and loft conversions across Greater London. Costs are generally based on a % of the build cost.

At Draw Plans we are open to all sorts of informal or flexible arrangements that will help you to bring your project to a successfull conclusion.


10: Key Stage Project Management Service / OPTIONAL

Our Key Stage Project Management Service is a more popular option for homeowners. Having an experienced Project Manager by your side for the entire project will ensure you get an on-time on-budget build with no nasty surprises in the final account.

Draw Plans Cost £ 995 Plus Vat


11: Fixed Price Build Contracts / OPTIONAL

A Fixed Price Build Contract can be a great option if you want to use one main building contractor to build your extension. It may cost a bit more but you know from the start where you are with regard to finances.

You can also opt for a Penalty Clause in your build contract to ensure that the work is carried out on time.

Retentions are also a popular option to ensure that defective or faulty workmanship is put right after the build.

Draw Plans will be happy to arrange a Service Provider Contract for specific trade services or for a Fixed Price Build Contract.

This a FREE Service for clients who have instructed Draw Plans for the Key Stage Project Management Service.

Draw Plans Cost £ 195 Plus Vat (To Prepare a Fixed Price Build Contract Ready for Signing)


12: Cost v Value - Choosing a Designer

It all sounds easy enough, just place an enquiry online and wait for the quotes to come in and then pick the cheapest quote. You might save £100/£200 or even £300.

But before you do that you really should consider a few other factors and ask yourself:

  • Do you really want to choose the cheapest designer to work with on what is probably one of the biggest projects that most homeowners do in a lifetime?

  • Do you really want to choose a designer with little or no experience?

  • Do you really want to choose a starving designer that doesn't know how to submit a planning application or deal with the planners?

  • Do you really want to choose a designer that doesn't know how to create your building plans for building control?

What about adding value to your home? Do you really want to try and save £200/£300 on the cost of your plans and miss out on the potential to add the most value to your home? In effect save a few hundred on the design plans whilst possibly missing out on £50k in added value.

Extending your home is one of the biggest investments you are likely to make so don't make the crucial error of hiring the cheapest designer that won't have the knowledge and experience to ensure that your project is a complete success.

An experienced designer will know exactly how to add kerb appeal to your property and how to add the most value. They will also be able to guide and support you throughout the entire process.

An experienced designer will know exactly how to reduce your build costs, locate the various trades, source the best deals on double glazing, kitchens, flooring and save you several thousand during the process.

Experience is crucial to the success of the build as is a designer that can provide a full range of architectural services to support you throughout the project.


13: Talk To Draw Plans TODAY!

Draw Plans will be more than happy to discuss your plans for an extension to your property. Talk to us today and you will soon discover why so many homeowners are choosing Draw Plans as their No: 1 Architectural Services provider.

020 3921 0745

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