The abodes of tomorrow will be pared back but it may be the owners who really change, writes Kate Robertson.

AS the designers of buildings that may last generations, architects have a vital role to play in creating a sustainable world.

The Age asked three experts to look into their crystal ball to predict what form houses are likely to take in the future and discovered owners might change more than their houses.

Jeremy McLeod, Breathe Architecture Architect Jeremy McLeod has four teenage daughters and one bathroom. His family has agreed on a morning shower roster and it works. But, he notes, "there's a big resistance in the market to going down to one bathroom".

 He sees resistance to downsizing and behaviour modification as one of the biggest barriers to overcome on the road to sustainable housing.

Australians need to understand that small and efficient houses are the only way forward, he says.

"We can design what we would consider to be quite a spacious home for an Australian family at 15 squares," McLeod says, including three bedrooms, kitchen and a single bathroom. Modern family houses are often 28 squares, with multiple bathrooms and living areas.

"The whole thing about people having two bathrooms or three bathrooms or a bathroom for each bedroom is a sustainability disaster. The bathroom is the most energy-hungry or material-hungry room in the house.

"Design efficiency brings in sustainability in itself to bring down your carbon footprint.

There's less materials to maintain, less that goes into the building initially; there's obviously less cost, there's less heating and cooling. It's a no-brainer."

On McLeod's wish-list are restrictions on the size of houses and a greater preparedness of clients to "walk the talk" by doing things such as putting on an extra layer during winter rather than relying on heating.

"In our office we don't have air-con in summer. For those really hot weeks we start at seven and finish at three, before the building starts to heat.

I guess we are asking a lot of people but we think that desperate times require desperate measures."

Associate Professor Ralph Horne, director of RMIT's Centre for Design The greening of Australia's urban landscape is going to be radical, according to the director of RMIT's Centre for Design, Associate Professor Ralph Horne.

Houses are going to look different and the materials used and the methods of building them will evolve, as will the occupants' behaviour.

"Cities never have been static entities and we should embrace diversity and change over the next 20 years ... it's not putting us into some kind of eco-straitjacket. We will be building homes in very different ways."

Professor Horne says more components will be made off-site, which will improve accuracy, reduce wastage and enable recycling.

We may still be using familiar materials but we may be using them in different ways and in different combinations.

"The dominant construction form at the moment is brick veneer on a concrete slab and if you were to push that toward the envelope ... you will reach a limit of what can be done.

What we really need to do is rethink the whole thing."

Professor Horne says some volume builders are already getting on board by offering six and seven-star energy-rated houses, although that system has its limitations.

"The star-rating system only points to the operational efficiency of heating and cooling and it makes all sorts of assumptions about how we use heating and cooling," he says.

"You could have a seven-star building but if the occupiers of the building crank up the heating, the bills and the greenhouse footprint might be higher than a three-star building that is used more intelligently or sparingly."

In 10 years' time, it will be easier to build zero-emission or carbon-positive houses through design improvements combined with behavioural shifts by the occupants that will reduce energy use to the point where it can be met by renewable energy, he says.

"Renewables on a house that is using 20 kilowatt hours of energy a day looks hard and you need a lot of (solar) panels ... but if you have a really energy-efficient house and you only use five kilowatts then that's perfectly doable."

And Professor Horne is optimistic home owners will be open to making those changes, citing the cultural shift that has enabled water use per capita in Melbourne to fall.

Riccardo Zen, Zen Architects A greener Melbourne will be a more lively city with increased housing density, according to the director of Zen Architects, Riccardo Zen. "We are consuming a lot more land and materials than we need to," Zen says.

"We are going to see more interesting and diverse examples of urban consolidation, particularly in the inner city.

 We are going to see a lot more height in our suburbs.

 Density can create incredibly vibrant areas by lifting the amount of activity that goes on there."

In the future, more value will be placed on aspects of housing that are, essentially, free: renewable energy, rainfall, a fresh breeze, a borrowed landscape from a neighbour or a nearby park.

"Our goal should be to come up with the most environmentally benign buildings that we can ... which might mean we start to see lots of things we have already seen before ... the classic fruit trees and vegie patch of the '60s and '70s might be reconfigured into a much more productive and compact space.

They may even end up on the roofs of our buildings or as street trees."

Houses will be smaller, energy use will decrease, water will be captured and recycled, while individuals should be rewarded with some sort of tax or rate rebate for their efforts.

"I would like to see a more mature and realistic approach to housing ... I think what people end up with is a combination of what they think they must have and can afford, what others will like and therefore what they can resell, rather than really understanding what they need."

Houses of the future

■Passive solar energy a part of every design

■Smaller houses

■Fewer bathrooms ■Productive gardens

■Locally sourced materials

■Greater use of the outdoor room

■Behavioural change by occupants

■Less turnover of interiors

■New building materials

 ■More off-site manufacture

■Improved energy-rating system