New Legislation Favors ADU Development

By Susan Bady

Accessory dwelling units, or ADUs, continue to make a big impact on the urban landscape, as city planners craft legislation that make it easier to develop backyard space in established neighborhoods.

ADUs are an affordable housing option in cities where young professionals, as well as empty nesters, are being priced out of desirable neighborhoods. Homeowners can rent ADUs on their properties to supplement their income—a real bonus for seniors—or to provide an independent living space for aging parents or other family members.

As is to be expected, the pace of ADU development depends on the law in each municipality. ADUs are currently permitted in such metropolitan areas as Austin, Texas; Boulder, Colo.; Minneapolis; Portland, Ore.; San Francisco; Seattle; Tampa, Fla; Vancouver, B.C.; and Washington, D.C. Two of the newest cities to adopt ADUs are Englewood, Colo., and Lexington, Ky., which announced their ordinances in 2019.

Other major metros are fine-tuning their ADU regulations to meet the needs of a changing population. In Atlanta, where the population grew 12 percent between 2010 and 2016, city planners recently adopted a zoning update that reduces off-street parking requirements and provides more opportunities for ADUs in single-family neighborhoods.

In California, a statewide ADU law establishes standards for local regulations governing ADU development, but local governments can still enact ordinances that make ADU development impossible or prohibitively expensive. This might mean extreme requirements for minimum lot size, setbacks, floor area, or open space, or other requirements that would make ADUs illegal on most lots. Other California cities impose high impact fees to discourage ADUs.  

Fortunately, help is on the way. In September 2019 the California state legislature passed three bills that, if signed into law, would remove most of these barriers to ADU development. Key features of the bills include:

  • No minimum lot size requirements
  • No lot coverage, floor area ratio, or open-space regulations that would prevent the development of an 800-square-foot ADU
  • No owner-occupancy requirements for five years
  • A cap of 4 feet on setback requirements, which opens up plenty of space for backyard ADUs
  • Significantly reduced impact fees

California Gov. Gavin Newsom has already signed a bill to prevent homeowners’ associations from barring ADUs.

Design is specific to the site

ADUs are typically small, but they’re not necessarily tiny. Whereas tiny homes range from 200 to 400 square feet, ADUs can be up to 1,300 square feet, including three bedrooms and a full kitchen.

Just as a new infill home ideally reflects the design character of existing homes in the neighborhood, an ADU is usually designed to be compatible with the primary residence on the lot. A good example of this comes out of Shelter Solutions, a design/build firm, has a thriving ADU business in the Portland, Ore., area, with 160 units built to date. A look at the company’s online portfolio shows how seamlessly the ADUs fit in, whether the design is Craftsman, contemporary, Victorian, or Tudor.

Shelter Solutions ADUs range from 380 to 800 square feet, with 700 being the average size, says Joe Robertson, owner of the Hillsboro, Ore.-based design/build firm. Most of the units are custom designed, with prices ranging from $150,000 to $250,000, Robertson says.

But since the Portland Planning Department amended the zoning code in 2016 to revise restrictions on small ADUs, the company has developed more affordable, predesigned and pre-engineered ADUs that fit the revised criteria. The predesigned models can be built within 5-foot, side- and rear-yard setbacks, which are closer to property lines.

They’re also designed for faster permitting and construction, says Robertson, and can be purchased as part of a complete turnkey package (everything from design to final inspections), or a do-it-yourself package where the customer is provided a weathertight shell.

Turnkey prices are $129,990 for a 16-by-24-foot model; $149,220 for a 20-by-24-foot plan; and $164,250 for a 24-by-24-foot model. Each unit has one bedroom, although the smallest can also be designed as a studio. The design evokes Northwest Craftsman style, with extended eaves and roof brackets. Homes are certified under the Earth Advantage green-building program. Standard features include low-maintenance, fiber-cement siding; roofing warranted for 30 years; ductless heat pumps; and in the kitchen, locally sourced, custom cabinets, slab countertops, and luxury vinyl tile floors.

Bright future for ADUs

New legislation is in the works to promote more ADUs in Portland and increase density. Among other things, the proposed residential infill program would allow a single-family home to have two ADUs or a duplex to have one. It also provides greater flexibility for ADU design, maintaining current ADU size allowances; allowing basement ADU conversions to exceed the 800-square-foot cap in an existing house; and allowing the front door of an internal ADU to face the street.

In Vancouver, B.C., ADUs are called laneway houses because they’re built on laneways, or alleys. Lanefab Design/Build has built approximately 100 laneway houses in Vancouver to date, all one-of-a-kind custom, says Bryn Davidson, a LEED accredited designer who leads the company’s design team.

Recently completed Lanefab projects are a mix of styles including Prairie, modern, Craftsman, and modern farmhouse. They range from 700 to 1,000 square feet and $360,000 to $460,000, which includes $20,000 for design and engineering; $30,000 in permit fees; $20,000 for site work; and $20,000 for landscaping. That’s cheap by Vancouver standards, where a new, 1,000-square-foot condo could run at $1 million, not including HOA fees.

Clearly, ADUs are a viable solution for high-cost housing markets with urban cores that are largely built out. They address three critical issues: affordability, rising construction costs, and the scarcity of buildable land. They also help homeowners by providing rental income or an in-law suite, and builder/developers with an extra income stream.


Post by Susan Bady, self-proclaimed “armchair architect” and advocate of sustainability, new building technology and most of all, good design. 

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