The RTB has published detailed guidelines on what constitutes a "substantial change" to a rental property for the purposes of exemptions from the rent pressure zone measures:-
https://onestopshop.rtb.ie/images/u...l_change_exemption_in_Rent_Pressure_Zones.pdf
https://onestopshop.rtb.ie/images/u...l_change_exemption_in_Rent_Pressure_Zones.pdf