There are concerns of an oversupply of apartments in Brisbane, Sydney and Melbourne. Credit:Angela Wylie So what's all the fuss about? These charts, compiled by UBS economists led by Scott Haslem, show why many in the financial sector appear are looking more closely at the apartment boom. 1. There is an apartment-building surge The number of multi-storey apartments being built has more than doubled in the past few years, and almost tripled since 2010, as this chart shows. The number of new houses, in contrast, has stayed more or less flat.

Digging further into the detail, UBS economists say high-rise apartments – those of more than four levels – appear to be driving much of the jump. They say the proportion of building approvals that are for high-rise developments has risen to a record of about a third of all approvals in recent years. Whether all these high-rise apartments will be snapped up by owner-occupiers or investors remains a point of contention. 2. If you thought there were a lot of cranes around, you are right. Rather than statistics, some people prefer more anecdotal indicators, such as the number of cranes around town. A crane index from Rider Levett Bucknall, a quantity surveying firm, shows the crane count is up 165 per cent since 2014.

Cranes are a useful gauge of construction activity, but building is also a cyclical business, meaning it has big ups and downs. For this reason, some also see the crane count as a potential sign of future risks. Indeed, the crane count is said to have been used by the former chief executive of National Australia Bank, Don Argus, on a trip to Melbourne airport back in the 1990s. It was then followed up with review of the bank's commercial property loans, and that helped it avoid some of the worst pain in a subsequent property bust. 3. Boom-time in Sydney, Melbourne, Brisbane This chart shows just how much Sydney, Melbourne and Brisbane have been driving the surge in unit construction. As the biggest cities, you'd expect that to some extent.

But the concentrated nature of the boom also raises concerns that in some inner city areas, there are more units being built than will be in demand. S&P said in their recent report they thought the potential for over-supply was greatest in Melbourne and Brisbane. Loading The UBS economists who came up with these graphs reckon Brisbane has the strongest chance of over-supply, after calculating the number of residential building approvals as a share of the existing dwelling stock. Even so, their prediction is for a "moderation" rather than a "downturn," arguing that "record low interest rates trump everything else". So far at least, the official figures on average house prices, including apartments, have been more resilient than many expected this year.