Proposed tax reductions on rental income, under consideration in the upcoming budget, would be an 'expensive and ineffective' way to keep landlords in the market.
Trinity College Dublin Assistant Professor of Economics Dr Barra Roantree was responding to suggestions that landlords could pay less tax on rental income.
It is thought the change could involve a lower rate of tax or increased exemptions for landlords.
Dr Roantree told The Pat Kenny Show any such approach would be unfair.
"What these things share is that they would be very expensive, very unfair and fundamentally just completely ineffective in dealing with the problem," he said.
"During the Celtic Tiger we encouraged a bunch of people to become landlords... and they're now approaching retirement.
"They don't want to be landlords, and that's one of the big reasons you have landlords leaving.
"I think what everyone's agreed on is we need a huge amount of more units; we need 40,000 to 60,000 units in the country per year."
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'It's hugely expensive'
Dr Roantree said tax reductions are unlikely to stop landlords from exiting.
"These tax cuts, what they would be doing is giving a taxcut to all those who are in the market already - whether they're thinking of leaving or not," he said.
"From that point of view it's hugely expensive."
Dr Roantree said around 160,000 landlords pay tax on that income.
"Say if you were to stop just 10,000 of them leaving with that [incentive], and I think that's incredibly optimistic, you're talking about €40,000 per landlord you've stopped leaving," he said.
"So it's an incredibly expensive and ineffective way from stopping them leaving.
"Rather what we should be doing is looking at what are the barriers to new supply, and what are the barriers to people becoming landlords, to investing in the market," he added.