The Building Regulations apply to most ‘Building Work’ and you need to make an application before proceeding. The definition of building work is contained in the regulations and in general, covers the erection and/or extension of any type of building (with certain exemptions), the installation of works and fittings such as new waste appliances, new drainage and heating appliances, alterations to the structure of a building, work affecting means of escape in case of fire and underpinning.
Building work does not cover minor repair items, but applies to replacing a roof covering. More details here (276KB) 
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Replacement windows or doors and domestic electrical installations (except certain minor works), must now meet Building Regulation requirements.
Different procedures may apply, do ask for further information by contacting our building control team who will be pleased to advise you.
Alternatively, you may wish to download this useful Building Regulations Explanatory Booklet. (1MB)
Under the Building Regulations 2000 certain buildings and extensions constructed at ground level can be exempt from the need to make a Building Regulations application if they satisfy set criteria.
Work which may be exempt include:
Please refer to the guidance sheet for the criteria and further information.
Compliance with the above criteria only exempts the works for Building Regulation purposes and you should check whether Planning Permission is required for the proposal by telephoning 0845 129 77 77 or 01298 28400.
If the proposal is to be constructed on or adjacent to a public sewer you should contact the relevant Water Company.