The leader of the Honolulu Board of Realtors said Oahu homeowners looking to help family, friends or even strangers with housing should look into the idea of creating an accessory dwelling unit on their properties.

ADUs, essentially secondary dwellings on residential lots, must meet certain building and land use laws, and building permits for ADUs are granted only in neighborhoods where there is sufficient infrastructure such as adequate sewer capacity. And the size restrictions on ADUs may limit how many occupants they may house.

But at a time when there appears to be a spike in the number of illegal rental situations, HBR President Sue Ann Lee is recommending creating an ADU as a legal way for owner-occupants to help ease the island’s housing demands while earning some rental money on the side.

“Somehow we have to find a solution to provide housing, even if it’s just a bedroom for some people,” Lee said. “ADU would help solve that.”

Hoping to increase the affordable-rentals inventory, Mayor Kirk Caldwell initiated the ADU program in late 2013 as part of his affordable-housing strategy. It was adopted by the City Council and went into law in mid-2015.

A minimum lot size of 3,500 square feet as well as adequate water and sewer capacity are among the main criteria. ADUs can be attached or detached from the original house.

They must have a separate kitchen, bedroom and bathroom, as well as a dedicated parking stall. ADUs must have a maximum size of 400 to 800 square feet, depending on the lot size.

Lee recommended that prospective ADU applicants hire architects or other design professionals to help guide them through the complex permitting process. A layperson could go it alone but would need to invest time and energy to understand the details of the process, she said.

“It can be done, except you’ve got to do a lot of reading,” Lee said.

ADUs are not the same as ohana dwellings, which require the occupants of the second dwelling to be related either by blood, marriage or adoption. Ohana units also have a different set of requirements from ADUs.

The number of ADU permits issued by the Department of Planning and Permitting is rising.

As of Oct. 31 the city had received 509 applications and approved 326 permits. As of July DPP had received 413 applications and approved 242.

In July 2016 Caldwell signed a bill allowing the city to give those with approved ADU permits a waiver of city sewer hookup fees and other charges associate with building permits.

City officials estimate the waivers would save ADU builders up to $10,000 each.

Submitted ADU applications must be processed by DPP within 60 days, but applicants are required to fill out a “pre-check” form before submitting a formal application.

To discourage property owners from turning an ADU unit into a bed-and-breakfast or other vacation unit operation, they must file declarations of restrictive covenants agreeing not to rent to a party for less than six months.

Go to DPP’s building permit page for more on ADUs.