Exempted Development Overview
Exempted development is development for which formal planning permission is not required. Categories of exempted development are set out in planning law and usually refer to developments of a minor nature such as small extensions, small home energy upgrades or gardens sheds. There are usually certain thresholds relating to, for example, size or height. Where these thresholds are exceeded, the exemptions no longer apply. There are also exemptions for some vacant commercial conversions. In some cases, you will need to formally notify the local authority of the proposed development 14 days prior to commencement of development.
Exempted Development Planning Legislation is viewable here:
The exemptions for converting vacant commercial units to residential units is viewable here
If you want formal confirmation from the Planning Authority that your works are exempt from requiring planning permission, you can request an official determination. This is called a Section 5 Declaration. Further details are available here.