Western suburbs "McMansions" should be converted into apartments to help deal with Perth's population growth, an expert says.
Leading WA environmental scientist David Kaesehagen said walls or divisions could be built within big properties in the most affluent suburbs to add to housing stock in a rapidly growing market.
Mr Kaesehagen, director of landscape architecture and environmental science firm Ecoscape, was among a panel of experts who spoke at a Committee for Perth event last week on population growth in cities.
The Australian Bureau of Statistics has forecast Perth's population will grow from 1.8 million to 4.2 million in the next four decades.
Urban planner Julian Bolleter, who gave the keynote address, said planners must be more creative about handling population growth and increasing density in suburbs.
Dr Bolleter, who co-authored the book Made in Australia, which explores the challenges of future population growth, said the "Australian dream" needed to be rethought.
"Perth is already the most sprawled city in Australia and possibly the world - we cannot keep sprawling," Dr Bolleter said.
"We need to increase density around public open space to maximise existing parks and reserves."
Mr Kaesehagen said with the right laws and incentives, owners of large mansions could be persuaded to divide their properties. "This is a way of using existing built form to increase density without introducing high-rise or changing the aesthetic of these established suburbs," he said.
"People's needs change as they age - this way they could live in the same area but have a smaller place.
"Nowadays, even if you grew up in City Beach or Nedlands, you can't afford to live there as adults - this way you could."
Nedlands mayor Max Hipkins said the suggestion was fanciful.
Mr Hipkins said people in the western suburbs liked space and homes were getting bigger.
"It doesn't make sense for people on the lower end of the socioeconomic scale to live here because food, petrol, doctors - it's all more expensive here," he said.