The previous government spent more than $50 million putting people up in motels as emergency housing, when only $2m had been forecast, the Housing Minister says.
Housing Minister Phil Twyford said the previous government's emergency and transitional housing had left him with some "ticking time bombs".
"Funding for 100 frontline staff - for emergency and transitional housing - runs out at the end of this financial year.
"This underfunding helped the previous government's Budget projections look better, but it didn't reflect the real costs of the policies," he said.
He also said the Housing First approach set up under National also had less than half the funding needed per place.