Almost one in seven of the population is now living in the private rented sector, the highest number on record.
A lack of mortgage lending and shortage of properties coming onto the market has resulted in a sharp rise in the numbers renting, with almost 700,000 living in leased houses, flats or apartments.
And there has been a surge in recent months, with 50,000 more people renting today compared with last December.
As many as one in three are reluctant tenants, and would prefer to live in their own home.
The increase in the numbers renting comes as 'The Rent Report' from the Irish Independent reveals that prices in our main cities of Dublin, Cork and Galway have soared in the past five years, while prices have plummeted in the regions.
New figures from the Private Residential Tenancies Board (PRTB) show that just 455,000 lived in private rented housing in December 2013. This has risen to 695,646 today, meaning the number has increased by 52pc in just 18 months.
The growth comes as the number of houses being constructed remains stubbornly low and well below the level needed to meet demand.
The rise in prices means that many of these tenants are unlikely to be in a position to save a deposit which would allow them to secure a mortgage under tough Central Bank rules.
In addition, mortgage approvals have stalled, with just over 2,000 issued in March this year.
The figures come after Government policy advisers the National Economic and Social Council (NESC) recommended that tenants should be offered longer leases, and landlords offered similar tax reliefs as apply in the commercial sector, in a radical shake-up of the market.
The NESC said that one in three renting was unlikely to be able to purchase a home in the near future, and that they should be protected in the event that the property is sold.
In an interview with the Irish Independent, PRTB director Anne Marie Caulfield said the private rental sector had doubled in recent years for a variety of reasons.
"People are renting because they may not be able to access a mortgage," she said. "Research suggests some 30pc of tenants would buy if they could, but cannot get access to a mortgage or cannot save a deposit or their employment isn't secure.
"In a period with very little direct building, it is playing an important role. Roughly one-third have said it suits their needs because they can live in an area with family supports or where their children go to school. It also suits people on short-term (work) contracts."
But she warned that the sector faced serious issues, including the fact that some 40,000 buy-to-let mortgages were in serious mortgage arrears.
"If they were to be sold and the tenant was affected, that would be quite serious," she added. "Supply and increases in rent are the biggest issues. The NESC report talks about rent stability measures, whether the Government takes them on board is another matter."
A report commissioned by the PRTB last year said that rent controls might not be appropriate as they could affect supply.
But if landlords signed up for longer-term leases with tax incentives, it could result in rent certainty over the longer term. This would also level the playing field for those considering investing in residential or commercial developments.
It is believed that around 92pc of all tenancies are registered with the PRTB, and there are some 170,000 landlords in the market. In addition to the 700,000 living in the private rented sector, another 130,000 are local authority tenants.
Overall, there are some 323,000 tenancies registered, which are home to almost 700,000 people.
Ms Caulfield said that some 19,641 warning letters were sent to landlords in 2014 reminding them of their legal obligation to register a tenancy, which costs €90. Each new tenancy must be registered, and existing agreements updated every four years.
It is believed that around 9pc of tenancies are not registered. However, data from the Department of Social Protection - which pays the rent of around 100,000 people in private accommodation - is used to track offenders.
Failure to register incurs a €180 late registration fee. In recent years, two landlords have been forced to register 120 tenancies each over a period of time, incurring a bill of €21,600.
Ms Caulfield added that 17 summons were issued last year for non-registration, with seven landlords convicted. Fines and costs of €95,770 were awarded against these individuals.
The PRTB noted that landlords were not obliged to inform it when a tenancy lapsed, adding that a tenancy lasted for up to four years if one original tenant remained in the property.
However, these caveats would also have applied in previous years, when the number of registered tenancies were far lower.
The NESC report also said the PRTB, which is tasked with supporting the rental market and resolving disputes between landlords and tenants, should be given more resources.
The agency employs 30, and has been given sanction to recruit an extra 11 staff. However, there are plans to increase its workload whereby it will hold deposits on behalf of landlords, to be returned at the end of a tenancy. It will also take control of Approved Housing Bodies which provide accommodation to the elderly and those on low incomes.