A Commencement Notice (CN) is a notification to a Building Control Authority (BCA) that a person intends to carry out either works or a Material Change of Use to which the Building Regulations apply. The notice must be given to the authority not more than 28 days and not less than 14 days before the commencement of works or the change of use. Once validated by the building control authority, works must commence on site within the 28 day period. In the case of large developments, it is practical to submit a CN for each phase. The number of units scheduled to commence under a specific phase should be recorded in the CN. Number of single residential units commenced - the total number of one off residential units which are associated with the commencement notices submitted for that month. This figure is included within the total number of residential units commenced. The Local Government Management Agency (LGMA) operates the Building Control Management System (BCMS). It facilitates CNs to be submitted online. The Department cleans and collates the data before publishing it on a monthly basis. This data series on commencement notices is available from March 2014. It is broken down by local authority, number of notices for residential development, number of residential units and the number of one-off residential units. More granular data on commencement notices can be found at https://www.localgov.ie/ Data from March to May 2019 has been revised. The figures for those months were originally under-stated due to a data processing error.