OTTAWA -- A Liberal government fond of promising help for those working hard to join the middle class put its money where its mouth is Wednesday, unveiling a new housing benefit for low-income tenants, billions of dollars for repairing existing affordable housing units and a vision for building 100,000 more.

The portable housing benefit could eventually help 300,000 households after 2021 -- when the money is to start flowing -- and 2028 by providing on average $2,500 in help, and could go to those already in social housing and those on wait lists for a unit, the government says.

A new financing program will be established to allow housing providers to help them repair aging units, and to use their assets to leverage additional cash in order to build new apartments and homes. The $15.9-billion housing fund will create 60,000 new affordable housing units and allow repairs to 240,000 more, through grants and loans that prioritize mixed-income developments.

The document also says the government plans to create a federal housing advocate and table legislation to enshrine housing as a human right, requiring regular reports to Parliament on federal efforts to ease the housing burden for hundreds of thousands of families.

Although the Liberals are touting some $40 billion in spending over the next decade, the math includes almost $10 billion in planned spending, repurposes $4.8 billion in existing spending and relies heavily on the provinces and territories to add billions in matching funds.

The housing benefit, for instance, is supposed to be $4 billion over eight years, but that figure includes $2 billion from provinces and territories. Any province or territory that balks at the idea won't see the benefit.

That means the Liberals will need months to negotiate funding deals with provinces and three years in the case of the housing benefit.

Federal funds won't start to flow until next April. It's also unclear how much will be spent annually.

The reason much of the money won't be spent until after the next election in 2019 is because the federal government needs to take the time to get the details right and satisfy myriad local, provincial and territorial needs, Prime Minister Justin Trudeau said Wednesday at an event in Toronto.

"We are looking at the realistic horizon that is going to not just put a Band-Aid on the problem, but create the kind of deep change and lasting impact that we know Canadians are going to need," Trudeau said.

"When we say the federal government is back for the long term, we mean it -- and that starts with getting it right from the very beginning."

While the Liberals are touting a renewed federal investment, housing advocates say the document marks the start of more work to ensure the money actually makes a difference.

Leilani Farha, United Nations special rapporteur on housing, said the right-based approach in the document should be a major step towards reducing homelessness, although she acknowledged the plan remains short on details.

Jenny Gerbasi, president of the Federation of Canadian Municipalities, called the strategy a major first step, although she called on the government to explain how local input and ideas would be taken into account.

The Canadian Alliance to End Homelessness urged the government to move quickly to put the money in the strategy to work.

Recently released census data found that 1.7 million households were in "core housing need" in 2016, meaning they spent more than one-third of their before-tax income on housing that may be substandard or does not meet their needs.

The government hopes that building 100,000 new affordable housing units, along with billions more in spending over the next decade, will lift 530,000 of those families out of that core housing need category, help 385,000 more avoid losing their homes and lift 50,000 out of homelessness.

The Liberals laid the financial backbone for the plan in this year's federal budget, promising $11.2 billion over a decade in new spending. The Canada Mortgage and Housing Corp. is expected to turn about $5 billion of that money into $15 billion by leveraging private investment.

Still, most of the money won't be spent until after the next election, which troubles anti-poverty groups. Those groups staged demonstrations in multiple cities, demanding the Liberals spend the full $11.2 billion before the next election.

Wednesday's news included precious little help for Indigenous communities, which is getting a separate plan that Trudeau said the government is still working on finalizing. Separate plans are in the works for First Nations, Inuit and Metis, the document says.