The Dapper Doctor Don Brash once lamented political principles saying the process forces you to hide them, to keep them like roses in a box but unfortunately when you come back to them, they're dead.

That may have been the case for him in politics but he'll be pleased it didn't turn out that way for him when he was The Don of the banking industry, The Guv of the Reserve Bank.

In his view those principles saw him taking a stand on the high cost of paying a mortgage, which of course he had a great deal of power over in those days, saying it was better renting a home rather than buying one.

It was a principled stand for The Guv who was a renter in those days, but clearly as the economic tiller man he kept his roses in a vase, and now they're blooming. In fact he traded in the principle for a house in Auckland some time ago and is now, like many, a housing millionaire in that city which is among the dozen most expensive places on earth to get into bricks and mortar.

It'll become even more attractive now that the current Guv Graeme Wheeler again dropped the rate it charges banks for money, which means they're getting it for less, meaning those after mortgages will pay them less.

That'll stoke the housing market but the Guv was caught between a rock and a hard place, how to stimulate the economy while at the same time keeping house prices under control.

With real estate investors expecting house inflation to grow at 75 percent over the next five years, the latter objective is a big ask, with cheaper mortgage rates unlikely to quell their enthusiasm.

Houses in our biggest city are being built as fast as builders are able to ram nails into four by twos and therein lies a potential problem.

As buyers in the city look at the possibility of realising their windfall, by moving to other cheaper centres, Auckland could potentially end up with a glut of properties for sale and that's where the bubble can burst.

It happened in Ireland which was known as the Celtic Tiger up until 2007. An eventual oversupply saw house prices dropping by 35 percent over the next three years. At one point in Dublin house prices were down by 56 percent from their peak while apartments had dropped by 62 percent.

There's a similar risk here with the current building boom.

It's worth considering, when the property is actually worth less than the mortgage, ownership becomes meaningless!