A new study that came out this month from the Urban League suggests that replacing broken windows and missing doors on blighted, uninhabited properties is a cost-effective way to increase the health, safety and well-being of residents in poor urban neighborhoods.

The report, Urban Blight and Public Health, shows that more than five million families in the U.S. live in substandard housing. These structures can contribute to a variety of physical and mental health problems, such as asthma, lead poisoning and depression.

These families also tend to live in neighborhoods full of abandoned buildings with broken windows, which can “create a climate of social and psychological disorder that attracts criminal activity and violence,” according to the report.

The idea is based on the influential “broken windows” theory of urban decay, which was introduced by social scientists James Q. Wilson and George L. Kelling in the 1980s. An excerpt from their theory reads: “Social psychologists and police officers tend to agree that if a window in a building is broken and is left unrepaired, all the rest of the windows will soon be broken. This is as true in nice neighborhoods as in rundown ones. Window-breaking does not necessarily occur on a large scale because some areas are inhabited by determined window-breakers whereas others are populated by window-lovers; rather, one unrepaired broken window is a signal that no one cares, and so breaking more windows costs nothing.”

Detroit, Baltimore and Cleveland are among cities targeting blighted properties for demolition, but one municipality is showing that it’s possible to replace doors and windows in abandoned buildings and reduce crime and despair in poor neighborhoods.

In 2011, Philadelphia began targeted enforcement of its Doors and Windows Ordinance, which is intended to reduce the crime that’s often associated with vacant and abandoned buildings.

Property owners can be fined $300 a day for every opening that’s not covered with a functional door or window on city blocks that are more than 80 percent inhabited. Plywood board-ups are not allowed under the law.

To make compliance easier, the city does not require renovation permits to meet the Doors and Windows Ordinance. Inspectors aim to visit properties every 35 days.

Early research found that home sale prices increased an average of about 31 percent in neighborhood clusters where the ordinance was enforced versus a 1 percent increase for comparable properties.

Additionally, “building remediations were also significantly associated with reductions in violent gun crimes in one city section [and] building renovation permits were significantly associated with reductions in all crime classifications across multiple city sections,” according to the report.

Researchers concluded that enforcing the Doors and Windows Ordinance offers “a relatively low-cost method of reducing certain crimes in and around abandoned buildings. Cities with an abundance of decaying and abandoned housing stock might consider some form of this structural change to their built environments as one strategy to enhance public safety.”

The results echo a 2016 study of over 5,000 abandoned buildings and vacant lots in Philadelphia that showed firearm violence fell 39 percent in and around areas where doors and windows were restored—decreases that held up to nearly four years after the intervention.