Small changes could fully fund the program and produce many more affordable homes in desirable areas.

In 2016, when Portland's city council voted to start requiring a share of homes in new buildings to be made affordable to lower-income Portlanders, some predicted disaster.

"Could well make the city's housing affordability problems demonstrably worse,"

urban economist Joe Cortright warned.

Others rejoiced.

"Would harvest the windfall profits that our wildly inflated housing prices are creating,"

John Mulvey, a housing advocate with the East Portland Action Plan, predicted.

Others said that it might need to be adjusted in the future.

"At the earliest possible stage, if there is a need for us to reconvene and rethink any part of it. I want to make sure that that's baked into our policy,"

City Commissioner Nick Fish said.

Well, it took six years for the city to get around to it, but that self-assessment is finally underway - and it points the way to a handful of relatively modest changes that could mend (and not end) a program that looks like a pretty good deal for both tenants and taxpayers.

Since last fall, I've been honored to serve among 10 fellow Portlanders on the city's volunteer "inclusionary housing calibration work group" that has teamed with the city's staff and consultants to dig into the program's numbers, goals, outcomes, and future. Though there have been a few moments of healthy tension, the process left me impressed by the city staff's interest in getting the details of this policy right.

In that time, I've also learned just how unusual Portland's program is among similar "inclusionary zoning" programs. The key difference: unlike almost all similar programs in the United States but like more productive flavors of inclusionary zoning such as this one in France, Portland's program is at least partially funded.

In Portland, the public pays for the program in the gentlest of ways: by waiving some taxes and fees on buildings that comply with it. And as the city's contractor found, that waiver can potentially be enough to make the program work. The catch: if the program will both maximize the number of below-market homes and avoid driving up market prices, it needs full funding.

With just a few tweaks, criticism of Portland's program would likely recede. In fact, it can become a model for other North American cities that want to mandate mixed-income homes in new buildings.

Here's what that would take.

1. DEFINE SUCCESS

Portland's program has an essentially qualitative purpose statement: the program should "increase" the number of less expensive homes available in areas with "superior access to quality schools, services, amenities and transportation," especially affordable to households making less than 60 percent of the city's median income. (For a one-person household, that's $47,400; for a three-person household, it's $60,960. At those incomes, federally defined "affordable" rents, including utilities, are capped at $1,185 for a studio, $1,524 for a two-bedroom, and so on.)

Having a purpose is good. But Portland hasn't actually set any quantitative criteria for the city to judge this program's success or failure. This is bad.

Here's one simple figure that could be used to evaluate the success of the program: not just to "increase" but to maximize, given available public resources, the number of new homes in desirable areas that are affordable to Portlanders making 60 percent of the median income.

This is a crucial difference. Any construction at all under a mandatory inclusionary housing program will "increase" the number of below-market homes built, compared to a city with no such program. Someday, Portland might mandate that 40 percent of homes in new buildings have regulated affordability, with no public funding to offset those costs. If that set of rules resulted in a single 100-unit building each year, the current program language would count those 40 homes as a sign of success.

But in a city of 600,000, just...