Banks prefer a McMansion

President of the ACT chapter of the Australian Institute of Architects Tony Trobe said he had been effectively forced to change designs to give clients extra bedrooms they did not want or need, just so they could get finance from their banks for the build.

''The banks are saying 'no' because they think it's not as easy to sell a stylish two bedroom house as is to sell a three bedroom house with a garage,'' he said.

''I designed a home for a couple in Uriarra, which was to be done in two stages - the first was with two bedrooms and the second stage was later if they wanted it,'' he said.

''They didn't have children yet and didn't need the extra bedrooms, but they wanted it set up so it could become a full family home down the track.''

The ''Uriarra project'' became a three-bedroom home with two living rooms and an extra living area. It was not the first time it had happened.

Australian Bankers' Association chief executive officer Steven Munchenberg said there was no hard and fast rule about needing at least three bedrooms.

''Nobody in the industry is saying 'no more two bedrooms' but the banks will take into account the re-salability of the home,'' he said.

''It's not only in the case of a mortgage repossession, but if the owner wants to sell, the bank needs to be confident it will get a proper price.

''If you want to make a house shaped like an enormous turnip and there's no chance of getting the money back, then that won't work.''

Mr Munchenberg said banks also took into account their own loan books and the need to spread risk over a range of areas.

''The bank has to consider whether it's over-exposed to one style of property,'' he said.

Mr Trobe said it was important for Australians to try to reign in the big house obsession - no matter what motivation was driving it.

''We build the biggest houses in the world on a per capita basis and there are less and less people in them,'' he said.

''Affordability is an issue and the environmental footprint is an issue as well.''