Some housing economists believe that “granny flats” could be the key to alleviating housing shortages across the country, and they are calling on more municipalities to ease up the rules to allow such dwellings to be built on or into more single-family homes.

Nicknamed “granny flats,” these accessory dwelling units tend to be separate, cottage-like structures, but may be a converted garage or basement that houses an extra living area. Some city and state governments have zoning laws that prevent these extra living quarters from being added into single-family homes.

But that is changing. In California, three new zoning laws in 2017 allowed for expanded development of granny flats. California has since seen a 63 percent increase in the number of building permits for these units — more than any other state, according to ATTOM Data Solutions, a real estate data firm. Hawaii saw the next largest increase at 31 percent, followed by Tennessee at 25 percent and Washington at 22 percent.

“At a time when many housing markets are experiencing severe supply constraints and housing affordability is under stress nationwide, accessory dwelling unit legalization represents a low-profile free-market solution that requires little from government actors beyond getting out of the way,” said Jonathan Coppage, a visiting senior fellow at R Street Institute, a think tank, in a 2017 report.

Granny flats also might allow more homeowners to generate extra income from short- and long-term rentals of these units.

But many counties either still have zoning restrictions that don’t allow these units, or they are making the building permit process difficult.

Some counties, however, are concerned that the extra dwellings could lead to limited parking spaces and more congestion on their streets from tenants renting the units.

This article was contributed to The Log by National Association of Realtors.