The Seattle City Council should loosen restrictions to encourage more homeowners to convert their basements into accessory dwelling units.

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WHEN I was in my 50s, with my son out of the house, I began planning to supplement my income by turning my half-finished daylight basement into a mother-in-law apartment. Now that I’m retired, it allows me to stay in my home and afford the city’s ever-increasing property taxes.

Mother-in-law apartments are carved out of an existing home, most often in a basement, or sometimes in an attached garage. Backyard cottages, on the other hand, are more complex to permit, design and build. They’re about 10 times more expensive, likely to rent for market rates and they raise lots of concerns with the neighbors.

The Seattle City Council should separate mother-in-law apartment legislation from backyard cottages. They are the best and least expensive way the city can encourage moderately affordable housing.

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Mother-in-law apartments present fewer controversial elements than backyard cottages: They bring limited need for off-street parking, they’re owner-occupied and easy to permit because the footprint and appearance of the house don’t change, and no sewer hookup is required. They’re affordable because most owners are looking for a trustworthy housemate and want to minimize turnover.

Mother-in-law apartments are 100 percent owner-financed, often with a small loan against the owner’s equity. I built mine for $25,000, including $5,000 for a “bedroom egress window” that required cutting into the foundation. My apartment was inexpensive because, like many midcentury houses, my home had a daylight basement with a half-bath, a half-finished rec room and an outside door. Carving it into an 800-square-foot, one-bedroom apartment and adding a kitchen and shower was relatively easy.

The biggest barrier to more legal mother-in-law apartments in Seattle is the requirement for off-street parking in single-family zones. A proposal to eliminate this rule was ready for a City Council vote more than a year ago, but it was set aside for the HALA (Housing Affordability and Livability Agenda) committee to consider. With many people clamoring for single-family zones to absorb more of the coming growth in Seattle, adding a couple of cars per block seems a necessary change.

There are some other code elements that seem arbitrary, such as the requirement for separate circuit breakers and temperature controls in a new unit. The cost of shared heat and utilities and noise suppression are negotiated between my tenant and me. The city should roll back this requirement.

The best thing Seattle can do to increase density and affordability in single-family zones is to actively encourage mother-in-law apartments. Providing clemency for those who have violated certain requirements and eliminating other rules would go a long way toward encouraging these units, without any investment on the part of the city.

Families with adult children living at home, seniors wanting to live near their families without invading their privacy, individuals who need the rent to supplement their incomes and pay the ever-escalating property taxes: All would benefit from these changes.