Western Australia's Liberal party is promising to chip away at the state's housing crisis by removing outdated restrictions on granny flats.

Planning Minister John Day also announced that 500 affordable homes would be built on big state-owned blocks within three years, if the party is re-elected at the March 9 poll.

The Liberals also propose allowing granny flats to be rented by people other than relatives of homeowners.

At the moment, granny flats can only be used by the homeowner or their family members.

"By scrapping this old restriction, so-called empty nesters and seniors can unlock equity in their homes and receive a regular income, or provide space for a carer to live close by in their ageing years," Mr Day said.

"There is also potential for students and young people looking for affordable accommodation to rent granny flats."

Mr Day said the allowable floor space for granny flats would be increased from 60 to 70 square metres.

Regarding the new homes to be built by the state government, he said they would be made available for purchase under a shared equity program, allowing people who might not qualify for normal housing loans to own at least part of a property.

There are 100 people occupying existing houses on the lots who would be rehoused nearby and receive a moving cost allowance of up to $5000, Mr Day said.

The Liberals expect the program will be cost neutral by the time it receives revenue from the property sales.

WA Labor has long criticised the party for a sharp fall in land releases since it took power in 2008.

Opposition leader Mark McGowan says there's about 50,000 people on the public housing waiting list - and many wait seven years.

"In an economy of ours, I think that's too long," Mr McGowan said this week.

The average rental price in Perth is about $450 per week and it's not uncommon to see homes renting in the Pilbara's resources hotspots for $2000 per week.