The Portland City Council unanimously enacted new rules this week to require landlords to register the addresses of all rental units in the city each year.

The idea, city officials said, is to create an accurate citywide census of apartments and homes for rent and also make it easy to send communications to all renters and landlords. Landlords will submit the addresses along with their yearly city business tax filings.

That will require an estimated 10,000 or more landlords who haven't been required to file business taxes, because they gross less than $50,000 a year from their rentals, to begin filing.

The rules requiring landlords to submit the addresses of all their units kicks in for tax year 2018, meaning the vast majority of owners would need to send theirs in by April 15, 2019. But they can automatically get a six-month extension, officials said.

What's more, Mayor Ted Wheeler decided to make the requirement optional for the first year, until the city can better get the word out, plus work out the technology landlords will use to submit their information. The rest of the City Council present at Wednesday's meeting fully supported that decision. (Commissioner Nick Fish was away on vacation.)

The upshot is that a substantially complete census of Portland rentals can't be expected before late 2020, officials said. Commissioner Chloe Eudaly, elected in part on her pledge to help struggling renters, said she hoped landlords would see it in their own interest to comply in 2019 to generate reliable data about the rental housing supply.

The census bureau estimates that Portland has about 127,000 occupied rental homes and apartments. By its estimates, rental units make up nearly half of all homes inside the city limits.

City commissioners expressed strong support for the new registration system and their belief that better data will help the city make better policy decisions and communicate more effectively with tenants and landlords.

They made it clear they plan to charge a yearly registration fee beginning with tax year 2019. They did not say how high that might be, although they suggested it would be set high enough to cover the costs of running the registration program, estimated to be $565,000 a year.

Cities including Denver, Seattle, San Diego and even neighboring Gresham already require landlords to register rental units, Wheeler said.

Speaking for advocacy group Portland Tenants United, Anthony Bencivengo also called the change a "positive step forward" that he hopes will lead to mandatory safety inspections at all rentals and soon be accompanied by robust fees to support pro-tenant programs.

No landlords testified about the proposed registration requirement ahead of Wednesday's 4-0 vote.

Skyrocketing rents have left many Portlanders aghast over the past several years, and economists have said the laws of supply and demand mean that adding more apartments and rental homes is the only large-scale solution to make renting more affordable.

A new city rule requires nearly all landlords who build large apartment complexes to include discounted units set aside for renters of limited means or pay substantial fines. In the short run, that policy appeared to dampen developers' appetites for building such complexes more than it yielded a surge in new reduced-rent apartments.

Wheeler has vowed to get the 1,300 new rentals promised under the city's $258 million voter-approved housing bond built or underway before he leaves office. But that would meet only a fraction of what city housing analysts say is needed to house low- and moderate-income people in Portland.

-- Betsy Hammond