Honolulu Mayor Kirk Caldwell has a new plan for housing the island’s homeless, and it won’t necessarily be cheap.

On Thursday, Caldwell surrounded himself with human services providers from the both the public and private sectors as he outlined an ambitious two-year program that aims to get some of Oahu’s most visible and troubled homeless off the streets.

The project is based on a “Housing First” model in which resources are focused on getting people into shelters before worrying about providing the services they might need, such as drug treatment or mental health care.

Those services would be provided after an individual is entered into a home then chooses a service. Taking part in programs won’t be a barrier to entry into the homes.

The Housing First model has been used before in Honolulu, but without much success. One aspect that makes Caldwell’s plan different, however, is that the housing will be scattered across the island in places like Chinatown, Waikiki and Waianae.

In two years, Caldwell hopes to have as many as 100 of the island’s estimated 505 chronically homeless enrolled in his program, meaning they’ll have a permanent roof over their heads and have access to various social services.

The cost is estimated from $3 million to $4.5 million or about $30,000 to $45,000 per person.

But the money for Caldwell’s project is coming from a $35 million pot the city plans to get from selling 12 of its affordable housing units, which means it’s one-time funding.

The big question is where will the money come from should the program succeed. One projection says it could cost as much as $31 million a year to house Honolulu’s chronically homeless by the end of 2021.

Caldwell said the city will have to work with state and federal sources to obtain future funding. But he also said it would be premature to say exactly where the city would find money to house the homeless, considering the program is just getting off the ground.

“We’re talking about two years, it’s a pilot,” Caldwell said. “We’re going to see how it works and with that we’ll make a decision about how much money we’ll need and where we’re going to go to get it.”

The city prepared a 48-page report, called the Homeless Action Plan, that details how the Housing First program will work in Honolulu. It also highlights some of the financial challenges the city will face should the city continue the project beyond two years.

Costs nearly double to more than $7 million in the third year, the report shows, as the city projects the number of homeless it shelters will jump to 152.

By the eighth year of the program the city estimates the annual costs of Housing First will be more than $31 million dollars. This assumes that the city will be housing more than 600 chronically homeless individuals and providing them with the services they need.

The city report says the current federal funds the city receives to help pay for homelessness programs, such as Continuum of Care money from the U.S. Department of Housing and Urban Development, will be “insufficient to meet all the program needs.”

Money will have to come from other sources, such as Community Development Block Grants and general fund subsidies to help pay for the program. This could be a difficult sell at a time lawmakers, including the Honolulu City Council, are looking for places to save money. Any city funding changes will likely rely on getting council support.

To sidestep the uncertainty surrounding federal grants and earmarked funds, the report recommends the city turn to the private sector “to create an endowment fund to support the program funding necessary to support the long-term, uninterrupted effort to assist the most vulnerable population of unsheltered persons.”

City officials say that getting the homeless off the streets could save money over time. In particular, they pointed to the $15,000 the city spends every time it enforces its stored property ordinance, resulting in the removal of tents and other debris from city sidewalks.

That cost, they say, is more than the estimated $12,000 a year it costs to house a homeless person. That figure does not include support services.

Everyone is hopeful the plan succeeds, but they admit it will take some time to start seeing results. For instance, the city is hoping to get the first 25 chronically homeless into shelters by the end of 2014. By the end of 2015, officials are hoping to see anywhere from 75 to 100 homeless individuals in permanent housing.

“We’re ramping up and we want to do it right,” Honolulu Housing Director Jun Yang said. “We wanted to have a big, big number in the beginning and say, ‘Bang!’ But we really had to be more conservative and understand that this population is the most vulnerable and it’s also a population that is a little harder to service.”

He said the city can’t force people into its program, and he added that sometimes it takes between 14 and 15 attempts to get someone who spends the night sleeping in a city park to move inside.

One way the city will measure success is to see how many people stay in permanent housing for more than a year.

Honolulu Director of Community Services Pam Witty Oakland said the target is to get 85 percent of participants to stay off the streets. This would be similar to the “retention rates” Housing first programs in Seattle and Philadelphia have experienced.

She also described the plan as a “living document,” and that the numbers — including cost estimates — could change.

One of the biggest challenges, Witty Oakland said, involves getting everyone to work together under a new framework that requires dedicating financial resources to Housing First priorities.

Caldwell’s plan pulls together both state and federal agencies. It also incorporates buy-in from the many homeless service providers on the island, many of which specialize in different areas and get government funding to help the homeless.

Witty Oakland said the goal is to now bring all these groups together under one umbrella working toward the same goal, which is to focus on providing shelter before all else.

“It’s not simple,” Witty Oakland said, particularly when considering how the money is allocated for homelessness solutions. “It’s changing the business model for how the funding is organized and dispersed.”

Read Honolulu’s Homeless Action Plan here: