Can You Build a Backyard ADU for Your Aging Parents?
The short answer is: it depends on where you live, and you need to check before you plan. Zoning laws, local building codes, lot size requirements, and homeowners association rules all play a role. The rules vary significantly from city to city and county to county across the US.
The good news is that the regulatory picture has been improving rapidly. Under a series of new state laws that took effect on January 1, 2025, ADUs became easier to build in California than ever before, with new legislation eliminating owner-occupancy requirements except for junior ADUs, expanding the number of detached ADUs allowed on multifamily properties, providing a path to legalization of previously unpermitted ADUs, and relaxing setback requirements while increasing height limits.
Massachusetts moved similarly. The Affordable Homes Act amended state law to allow accessory dwelling units under 900 square feet to be built by-right in single-family zoning districts. “By-right” means no special permit or discretionary approval from a planning board – you submit plans, meet the standards, and you can build. Those regulations took effect on January 31, 2025.
California went further in late 2025. Governor Newsom signed four new ADU bills into law, including AB 462, AB 1154, SB 9, and SB 543. Among other changes, the new legislation expressly stated that local ordinances governing ADUs cannot unreasonably restrict the ability to create them. That’s a significant shift in how the state defines the relationship between homeowners and local planning rules.
For families looking to explore multigenerational living options for elderly relatives, the practical starting point is always your local planning or zoning office. Call and ask for their ADU handout and fee schedule. Ask specifically about setback requirements (how far from property lines the structure must be), maximum size limits, height restrictions, parking requirements, and utility connection rules. Also check with your homeowners association if you have one, as HOA rules can sometimes prohibit detached structures even where municipal zoning allows them.