What city officials are calling the nation’s strictest smoking ban is now in effect in a San Francisco suburb of 58,000.

The city council in San Rafael, Calif., unanimously passed a smoking ban last year that applies to any residence sharing a wall with another residence, whether owner-occupied or renter-occupied. After a year-long grace period and public-information campaign, the rule is now in effect.

“We based it on a county ordinance, but we modified it, and ended up making it the strictest,” Rebecca Woodbury, a policy analyst for the city, told ABC News.

The fact that the ordinance applies uniformly to multi and single-unit residences sets the San Rafael rule apart from similarly stringent smoking bans, Woodbury said. “The distinguishing feature is the shared wall.”

Smoking bans in multi-unit dwellings aren’t unheard of.  Indeed, just 40 miles away the city of Belmont has a smoking ban passed in 2009 that was at one point considered arguably the strictest in the nation, but it didn’t extend to all dwellings that share a wall with another residence.

Woodbury cited public health benefits as well as a UCLA study that found property owners could save $18 million a year in cleaning costs from apartments occupied by smokers.

Housing and public health authorities in recent years have called for policies banning smoking in multi-unit rentals. The Surgeon General concluded in 2006 that “there is no risk-free level of exposure to secondhand smoke.”  

It’s unclear exactly how many people in San Rafael will be affected, but multi-family housing (both owner-occupied and renter-occupied) makes up 44 percent of the market in the city, according to a city report on the ordinance before it was adopted. There are about 600 properties in the city with three or more units, which translates to 8,000 total multi-family rental units out of 23,636 total housing units.