Building Regulations are laid out by parliament and cover aspects of a dwelling such as fire safety, insulation, drainage and access.
You can either submit a Full Plan Submission or a Building Notice. The former requires more detailed advance planning, but could reduce the chances of you contravening any regulations. A Building Notice, by contrast, is the riskier (and potentially costlier) of the two, since you may only find out you have a compliance issue after work has been done.
In the case of single storey extensions, you can extend your house without planning permission up to three metres if an attached house or by four metres if a detached house. The maximum height of your single-storey rear extension is not higher than four metres.
For an agreement on any larger extension, you need to make sure you have the correct planning permission. Whilst not all extensions require planning permission in some cases (such as listed buildings or height restrictions), your plans could be halted before they start, or worse still, once they have started. Under ‘Permitted Development Rights’ in certain circumstances you can begin building without telling your local authority. You can check the criteria on your local council’s website on the Gov.uk website. A good idea is to pay a visit to your local planning office to ask them if what you have in mind will require planning authorisation.