The proportion of the population living in rented accommodation and the number of people per rental unit is at a record high and vacancy rates are razor-thin, meaning rental inflation will be with us for the foreseeable future according to a new report on the private rental sector from Savills.

Author of the report - John McCartney, Director of Research at Savills - said the number of people in an average privately rented households was "pretty steady for ten years until the start of 2016.

"Since then we've seen it increase quite sharply and i think a reasonable interpretation of that is there is just such a scarcity of rental properties available.

"We estimate the vacancy rate is at 1.3%. People are having to club together and of course costs come into it as well.

"Rents now are higher than they were back in the boom and this means that people are trying to club together to make the rent and what we're seeing is that maybe 18 months ago in a two-bed apartment you would have had one couple in there and they would have the spare room for visitors or storage.

"Today they're moving into a one-bedroom apartment, and who's going into the two-bedroom unit? It's two couples with four incomes making the rent."

On low vacancy rates, Mr McCartney said it tells us we are going to "have to do an enormous amount of construction before we get rents or indeed house prices stabilising.

"At the moment house-building activity is picking up but it's coming from such a low base that I think it's going be 3-5 years at least before we really start matching supply and demand."

Savills expects significant rental inflation until this change comes.

Mr McCartney said "Realistically we'e looking at rent inflation of somewhere slightly north of 5% so the rent controls within those RPZs limit annual rental increases to 4% but of course any new buildings or properties that previously weren't rented in the past two years that come on to the market can be set to market rates.

"So on a weighted average basis you'd be getting 5-6% rental growth there.

"Elsewhere in the country where rents aren't controlled and are coming from a very low base, I think we'll see rental increases of 7%-7.5 %."

The Savills Director of Research also said cash investors are beginning to squeeze out financed buy-to-let purchasers.

"Investors that have a high level of gearing - typically anything more than 40% LTV mortgages - are finding it very, very difficult to get a profit from renting residential properties, sot they're being squeezed out.

"But the good news is cash investors - and there's plenty of them - can make a very good profit at this if you look at the yield that's available to investors across Dublin - 4%-4.5% net - compared with deposit rates which are half a percent, so they're pouring in and they're forcing out the mortgage investors."

But the critical thing to say is ... in general the sector is growing so we shouldn't be trying to protect these mortgage investors, They've a failing business model because their cost base is too high.