Four new areas are to be designated as rent pressure zones (RPZs), as new figures show the average national rent now stands at €1,243.
The local electoral areas of Baltinglass in Wicklow, Piltown in Kilkenny, Sligo-Strandhill in Sligo, and Cobh in Cork will become RPZs from today.
It means that rents in impacted areas cannot be increased by more than 4% per year in both new and existing tenancies.
There are now a total of 42 local electoral areas and five local authorities classified as RPZs in Ireland.
Meanwhile, figures from the Residential Tenancies Board (RTB) show that in quarter three of this year the average national rent was €1,243 per month - up 8.2% in a year.
The data also shows the rate of increases is beginning to stabilise in Dublin and Cork cities.
A 6.6% year-on-year increase in Dublin is the lowest since 2017, while a 1.4% increase in Cork is the lowest since 2015.
Overall, the average monthly rent in Dublin in Q3 was €1,762 (up €110 compared to Q3 2018), and in Cork it was €1,192 (up €16).
However, the increases are more significant in other cities - including a 16.4% year-on-year increase in Waterford City, where the average rent in Q3 was €839 (compared to €721 in Q3 2018).
Rosalind Carroll, director of the RTB, explained: "Dublin and Cork City are the longest standing RPZs, so it is encouraging to see initial signs that RPZs are having a dampening effect on rents, and we hope to see similar stabilisation occur in other areas over time.
"We also expect to see some stabilisation in future quarterly reports particularly outside Dublin, as this sample reflects recent legislative changes which now require landlords of student specific accommodation to register their tenancies with the RTB.
"To date, we have received over 27,000 registrations for student specific accommodation."
