At the age of 30, the successful life Peter Watson had built crumbled.

Key points: An emerging class of landlords are offering their properties for lower rent to tenants who need a hand

An emerging class of landlords are offering their properties for lower rent to tenants who need a hand There's a push for state and territories to offer land-tax exemptions as an incentive to landlords

There's a push for state and territories to offer land-tax exemptions as an incentive to landlords Stock of social housing has barely grown in 20 years, while Australia's population has increased by 33 per cent over same period

"I lost my house, my business, my cars and went bankrupt," he said.

For six months he was homeless, surviving on the generosity of friends.

"Luckily, I still had a good supportive network around me, I crashed in the spare bedroom of one of my mates," he recalled.

"It was somewhere to stay but it didn't help my mental state because it was temporary."

Over several years, Mr Watson slowly got his life back on track and he became a successful entrepreneur.

"Now I'm in a position where I can help people who don't have financial resources or a support network to give them a second shot," he said.

Mr Watson is part of an emerging class of landlord, trying to use his secure financial position to help others facing homelessness.

Peter Watson's properties are listed with a not-for-profit real estate agency. ( ABC News: Simon Winter )

Using the not-for-profit real estate agency HomeGround, landlords are renting out properties at sub-market prices.

Businessman Phil Endersbee was one of the first to see the benefit of property philanthropy and use the agency.

He said while it was asking landlords to forgo only about $30 in rent a week, it could be hard to convince people.

Phil Endersbee is pushing for land-tax exemptions as an incentive to landlords. ( ABC News: Sean Warren )

"It's a case of, forget the feel good — show me the numbers," Mr Endersbee said.

Of 326 properties listed with HomeGround real estate, 38 are privately owned and 14 landlords have offered their properties with no expectation of a rental return.

The remaining properties are owned by a community-housing organisation, and rented out at normal market price.

Mr Endersbee is now pushing for state and territories to offer land-tax exemptions as an incentive to landlords to offer their properties for lower rental prices.

His proposal is being considered by the Victorian Government as part of efforts to boost housing affordability across the state.

Apart from the feel-good factor, currently the only other incentive for landlords is a tax deduction.

The difference between the market rental price and the discounted rate can be claimed as a charitable donation with the Tax Office.

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'It's the first proper home we have had'

Sub-market rental housing makes up only a small part of Australia's affordable and social housing.

Research by the Grattan Institute shows the stock of social housing — currently about 400,000 dwellings — has barely grown in 20 years, while Australia's population has increased by 33 per cent over the same period.

Single mum and casual worker Jo Tan was on the brink of homelessness before she was offered a house in Melbourne at 20 per cent less than market rent.

Jo Tan was facing homelessness before she was offered a rental home in Melbourne. ( ABC News: Sean Warren )

"I had started to apply for public housing and was looking at shelters that could take us," Ms Tan said. "I couldn't get sick because I couldn't afford it. It was really tough."

She recalls bursting into tears when she was told her application with HomeGround had been accepted.

It would be the first time her sons had their own bedrooms.

"It's the first proper home we have had," she said. "It's still at the top end of what I can afford, but it works for me."

More incentives needed for landlords

Census data suggests 10 per cent of private dwellings are unoccupied — but that includes holiday homes, and homes for sale or between tenants.

The director of the Melbourne Sustainable Society Institute at the University of Melbourne, Professor Brendan Gleeson, said incentives to offer properties at below-market rent should be tied to taxes on vacant properties.

"It's a stick to bring housing back into the market — so what about a carrot to bring those investors and landlords into the social end of the equation?

Half of all investment properties are owned by people who only rent out one property Number of properties owned by investor Share of total investment properties 1 50% 2 25% 3 11% 4 5% 5 3% 6 or more 6% Source: Grattan Institute analysis of ATO statistics 2014-15

"We have always thought of property investors as separate to the equation but this initiative shows that they have a role."

However, the Council of Australian Governments' (COAG) Affordable Housing Working Group estimates there is a $3,100 gap between what low-income earners can afford to pay and affordable rental rates, which is 75 per cent of market rent.

For a social-housing dwelling, where tenants rent at 25 per cent of their income, the gap is $8,850 a year.

According to the Australian Bureau of Statistics, 86 per cent of investment properties are owned by landlords with three or fewer properties.

Brendan Coates, from the Grattan Institute, said the land-tax exemption proposal would provide much larger incentives to those with multiple investment properties.

But for mum and dad investors, it might not be enough.

"The incentive is simply too small compared to the size of the subsidy needed to bridge the gap between market rent housing and what low-income earners can afford to pay," he said.

"In that context a land tax exemption worth only $500 a year to the average property investor in Melbourne, and nothing at all in Sydney, won't see many more affordable rentals made available."