ADA Friendly Areas (Information provided is for informational purposes only.  Be sure to independently check state and local laws for the most updated information regarding ADUs. 

New Hampshire is the first state to institute statewide ADU-friendly legislation, which won them the National Council of State Housing Agencies Award for Legislative Advocacy - State Advocacy in 2017. 

Portland Oregon - Due to high demand for affordable housing and housing shortages, Portland has embraced the ADU concept to help assuage those barriers to economic growth.  They are even waiving some fees normally associated with new construction to encourage this type of housing.

Seattle, Washington - this city is working to make ADU construction less restrictive by removing the requirement for two off-street parking spaces, permitting one attached and one detached ADU per property, and relaxing some development standards for detached ADUs.  While ADUs are commonly considered to be environmentally friendly, Seattle's program to encourage ADU construction was ironically postponed in May 2016, due to concerns about environmental impact.  An Environment Impact Statement was opened for public comment late 2017, and a final decision is expected in 2018.

Asheville, North Carolina - In 2015, the city changed their regulations to enlarge allowable ADUs.  Detached units can now be 70% of the primary house's size (up from 50%), with a maximum of 800 square feet. (The allowed height was reduced from 40' to 25').  Attached ADU sizes expanded from 50% of existing house's area (with a maximum of 500 square feet) to 70% (with a maximum of 1,000 square feet).  Additionally, Asheville is now permitting ADUs on lots that did not previously meet the size requirements based on zoning designation, which opens up many more properties.

Austin, Texas -When the city relaxed restrictions on the size and scope of SDUs in late 2015, it saw a 34% increase in permit applications.  Secondary dwelling units must be no larger than 1,100 square feet and at least 10 feet from the main house, on the same lot.

Santa Cruz, California - In addition to allowing ADUs, this city offers technical assistance, provides an ADU "how-to" manual for landowners, and further encourages ADU construction by offering pre-approved designs, low-interest loans for homeowners who wish to build ADUs on their property, and other tools.

Vancouver, British Columbia - This Canadian city has been particularly friendly toward ADUs, also called "laneway" houses.  Over 2,000 units, ranging from 600 to 1,000 square feet, have been built over the past decade.  Each unit requires a building permit, but the rules aren't as restrictive as many other communities.  For example, only one onsite parking space is required, regardless of how many dwellings are on the lot.

(Excerpted from The SRES Perspective)