Whether or not you need to obtain a building warrant depends on a number of different things. In order to make an assessment you will need to consider what type of property you have and whether anyone else may be affected by the work you want to do.
Some works are entirely exempt (Please refer to Schedule 1 of Regulation 3 here - PDF)
Other work may be exempt from the need to obtain a warrant. ( Please refer to Schedule 3 of Regulation 5 here - PDF)
Where the work you wish to do is not included within either of the above categories a building warrant will be required.
For additional information please see the links below or the Making an Application section:-