The Petaluma City Council last week took the final step to codify regulations aimed at encouraging more affordable housing development in a city beset by an acute housing crisis.

The council voted 7-0 to amend the General Plan to require that developers of large housing projects in Petaluma set aside 15 percent of their units as affordable housing.

The General Plan amendment, which passed without any discussion or public comment, was a formality at the end of a lengthy process to take steps to address a regional housing shortage that has put upward pressure on the cost of housing for many in the community. The council in September adopted the policy after much discussion.

With last Monday’s vote, the policy is now enshrined in the General Plan, the overarching document that guides Petaluma’s growth. The amendment was shared with the state Housing and Community Development Department, which sets housing targets for cities. The state had no objections to the city’s policy change.

Under the new housing policy, developers who do not set aside 15 percent of their units for affordable housing can pay a fee that is equivalent to 20 percent affordable housing units. Setting the in-lieu fee higher than the cost of providing on-site affordable housing is meant to encourage developers to build affordable housing with market rate residential developments.

The new rules are set to kick in on Jan. 1 and would apply to all developments that have not completed the application process by the first of the year.

The policy will no apply to developments already under construction, though some, like the Altura Apartment complex on Baywood Drive, have already agreed to set aside affordable units.

To illustrate the high demand for housing, Sonoma State University this month purchased for staff housing the entire 90-unit Marin Apartment complex under construction on Lakeville Street. The apartment complex was planned as market rate housing, but it takes off the market a much anticipated project that was expected to boost Petaluma’s housing stock.

(Contact Matt Brown at matt.brown@arguscourier.com.)