Landlords should retain the tenancy agreement, previous and new rent amounts, rent review notices, dates, proof of service and records supporting how the new rent was calculated. This may include comparable-rent evidence where required, along with payment records and correspondence about the increase. Keep the records for the tenancy and for long enough afterwards to deal with any RTB dispute or Revenue query; tax records commonly need to be retained for six years. The exact evidence needed can depend on the tenancy and the date of the increase, so check the RTB’s current guidance or consult a solicitor.