The Complete 9 Step Beginner’s Guide To Extending Your Home 

beginner's guide to extending your home

The Complete 9 Step Beginner’s Guide To Extending Your Home

So you’ve decided to extend your house. That’s a big decision to make but you’ve made it and you’re determined to do it, so now you need to know how to go about it, and how to get the best value for money in the build.

To help you, we’ve written this short guide to summarise the main considerations to bear in mind when extending your property.

It can seem like a daunting prospect, but the process is not as difficult or as scary as it may seem!

Planning Consent

planning permission help

The first question to ask yourself is, “Do I need planning permission?”. The chances are that you probably will unless your extension falls under what is known as Permitted Development. However, you will almost certainly need planning permission for your extension if it is more than one storey in height or is visible from a public highway or road.

If you are unsure whether your extension requires planning permission you can look on the Planning Portal website for more information, or contact your local authorities’ planning department.

In the event that your extension does require planning permission, you will need to complete a planning application and submit along with it the necessary drawings, information, and fee for the extension you are building. Most planning applications are submitted online via the Planning Portal website and guidance as to what drawings and supporting information are required can also be found there. But as a guide you will need at least the following:

  • A location plan at 1:1250
  • A site plan at 1:500
  • Floor plans of the building
  • Elevations of the building
  • A section through the building
  • You may also require a Design & Access Statement

Planning applications typically cost £172 for an extension and once validated, your planning application will take around 8 weeks to be determined by the local authority.

Tip: In the event that the application is rejected you can reapply for free within 12 months.

Once your planning application is approved you must start the building works within three years otherwise the application becomes void.

Planning can be a complicated process, with a number queries coming from the planning officers, or conditions being placed on the application itself. We would always recommend seeking advice from an expert, or if you are doing it yourself, making sure you do your own research on the topic.

Building Regulations

House extensions building regulations

The Building Regulations set standards that all new building works must meet. These are applicable to extensions.

In order to make sure that your extension complies with the Building Regulations, proposed drawings, details, and structural calculations will need to be submitted to your local authorities’ Building Control Department.

The council’s Building Inspector may come to inspect the works at certain stages to ensure that they are being completed in accordance with the Building Regulations.

At the end of the works the Building Inspector will issue a certificate confirming that the works comply with the Building Regulations. This is an extremely important document, especially when it comes to selling your property.

Depending on the complexity of your build, attaining Building Regulation’s approval either requires drawings and details prepared by your architect, or notification from your builder. The two difference types of applications are called Full Plans Application, and Building Notice. The former being for more complex works. For most extensions a Building Notice should be sufficient.

It is always better to ensure that the drawings you have prepared are sufficiently detailed enough for building regulation consent. Once these are prepared, your builder can then notify the Building Control department by issuing a Building Notice to the council, and they can manage the process for you.

How Much Will It Cost

Calculating the cost of an extension can only be as precise as the level of detail available in its design.

If you want a rough idea of how much your building will cost, it is typical for an extension to cost between £1,250 and £1,750 per m² of gross internal floor area (that’s the newly built area internally measured around the internal face of the external walls).

So if you have a single storey extension of 10m² you are looking at somewhere between £12,500 and £17,500 for the build.

If this same extension was then over two floors you can double that figure.

The cost is always dependant on the level of finish that you require, and the location of the works. London attracting the highest prices. It is also dependent on if you can get a good deal with your builder!

Will I Need An Architect or Surveyor?

The decision on whether you need an architect depends on your understanding of architectural design, the complexity of the build, and your understanding of the build process.

An architect will most definitely make your life considerably easier.

The architect should have a good understanding of planning and building regulations requirements, will prepare drawings and other documents for you, deal with planning queries, and can appoint and put in place a builder and building contract to cover the works themselves.

Architect’s Fees & Services

Architects fees vary depending on location and the nature of the works.

Typically for an extension you would expect to pay around 10% of the cost of the build for the architect’s fees.

Fees can be agreed as a fixed price, or on a percentage. A fixed price can of course give you cost certainty, however a percentage can provide you with a better deal if the value of the build comes in lower.

If you only require an architect for the design stage and not to oversee the works then it is always advisable to seek a fixed price. This is because they will only produce the drawings and submit them to the planning department. They will not oversee the works which is where the value of the works can change.

How much does an architect usually charge?

Well for a single storey extension in London you are looking at around £1,500 – £3,000. Again this is dependant on complexity.

The more complex the project, the higher the fee.

We have completed hundreds of extension across London and the south east and offer a free consultation and a very competitive quote. If you’re interested in extending your house, contact us and one of our team will be in touch to let you know how much it will cost.


Finding A Builder & Getting Quotes

Once you have planning sorted and your extension is designed you will need to get the thing built. If you have appointed an architect they should be able to recommend to you decent, reputable contractors to build your extension for you.

Alternatively you can find one yourself through recommendations from friends.

It is always advisable to get a few contractors to look at the proposed drawings and visit the property to give you competitive quotes for the works. Remember though, if one seems too good to be true it probably is.

Bear in mind that once a contractor has won a job if there are then any variations to the works then they can hike the price up for those as they know that they have no competition from other builders at that stage.

Again an architect or “contract administrator” / project manager will be able to manage the builder throughout the build and ensure they comply with any contract that they put in place.

Another method of getting prices for the works is to have an architect or surveyor prepare a tender package which can then go out to 3-5 contractors to competitively price. Talk to your architect or surveyor about this option.

Paying Your Builder

Once your builder is on site and the works are underway, they are obviously going to want to be paid.

Most builders require stage payments depending on the duration of the works. The schedule for payments should be agreed prior to appointing a contractor for the job, and some contractors will require an upfront payment.

If you are getting a loan for the project, this can be arranged to coincide with these payments and you should liaise with your loan provider to ensure you get the most appropriate loan for a building project.

If you have an architect or surveyor working on the project then they can manage the contractor’s payments, ensuring that they tally up with the work completed so that you don’t get ripped off.

Another word of warning when choosing a contractor is to make sure that they are financially stable and that they have sufficient insurances. You can check the financial position of a contractor by doing a company check on Google. You should also request to see copies of their Employer’s Liability Insurance, Public Liability Insurance, and All-Risks Insurance.

Try to avoid paying your contractor too much in advance because if the worst comes to the worst and they go under the chances are you won’t be getting that money back.

Always get your builder to provide you with a valuation of works that they have completed and check it against what you see on site, either yourself, or using a professional such as an architect or surveyor. Only pay them for the work that they have done!

Coping During The Build

Having your home extended is always a stressful experience. There will be lots of noise, dirt, and strangers on your property for a number of weeks or even months. It takes patience to remain calm.

The best thing to do is to ensure you have a builder that you are comfortable with and who you trust, and try to avoid getting stressed as much as possible. Talk to the builder and get him to tell you about what’s going on and when. It helps to know.

Your builder should know what they’re doing so it is best to let them get on with the job. If you are worried about their performance then you can consult your architect or surveyor, or get one in to ensure they are performing as they should be.

The Party Wall Act

One final thing to consider before you get started is the Party Wall (etc) Act. This Act of Government requires that building work which directly affects the adjoining structure between your property and an adjoining property, or involves excavation or construction on or near the boundary line, is not started prior to you giving notice and receiving consent for the works from your neighbours.

Your neighbours cannot prevent you from carrying out the works, but they can require that you have surveyors draw up a Party Wall Award.

This may seem like a side matter but it can add months to your project programme, and it can cost you thousands of pounds in surveyor’s fees.

Finally, good luck with your build and don’t forget to check out some of the useful links below to help you!

Kind regards

The Extension Experts Team!


Useful Links

Here are some useful links to help you do your research and get started.

Planning Portal – The main source of information for planning permission, and where you submit applications online
Party Walls Guidance – The Governments website for advice on complying with the Party Wall Act
Local Authority Search – Unsure which local authority to apply for planning to? Check out this link.
Building Regulation Advice – The governments guidance on complying with Building Regulations

If you have any other questions, we’d love to help. You can ask us anything at, or enquire here.

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