A commencement notice (CN) is a notification to a Building Control Authority (BCA) that someone intends to carry out 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.

CN's are early indicators of activity within a housing market. In a regular functioning housing market (outside of periods of negative price shocks), one would expect that the ratio of commencements to completions would average close to 100% making a suitable allowance for the lag between the two phases. 

This sub-section presents the total number of residential units commenced monthly and annually in Ireland. The data is presented through different variables such as total units commenced nationally, by local authorities, by local authorities in Dublin ,and the total number of units in the Greater Dublin Area (GDA).