One difference is that duplexes are separable whereas ADUs are not. Duplexes can be condo'd. ADUs cannot. An ADU will have much lower fees in many cities compared to a traditional second. ADUs are by right permits and have some state mandated streamlining so you should get a permit faster.
Most jurisdictions require the owner to occupy the ADU property. Oakland is an exception. But proposed state law, which is moving quickly, would prohibit that pesky impediment and void all existing deed restrictions on ADU owners. Even after the law changes many existing ADU owners may not become aware of their restored freedoms.
Local governments do not have to be as permissive as the state regarding ADU size. Many cities that have their own ADU ordinances have smaller size limits, such as 850 sf.
I see that San Francisco allows ADUs at multi-family properties, but I always assume provisions like that are tricks to persuade homeowners to give away their state mandated homeowner protections (such as signing a Costa Hawkins waiver). I am not aware of other jurisdictions with ordinances that allow ADUs at 2-4 unit properties. Please ID any in the Bay Area.
However, it makes total sense that ADUs should be allowed at multifamily properties. Talk about rapid deployment. Proposed state legislation would clarify original legislative intent. AB 881 would "require local agencies to ministerially approve ADUs on lots with multi-family residences and within existing garages."
AB 881 is also the bill that would eliminate owner occupancy as a condition of past and future ADU permits. This bill recently passed the Assembly floor by a vote of 71-2. It seems to be well on way.
Getting into the weeds a bit, but SB 50 would disqualify new development in any spaces that have been rented over the past 7 years. You should be careful not to trigger that harsh restriction if SB 50 passes. If you are in a jurisdiction like Berkeley or Oakland, then watch out because the rent boards in those jurisdictions do everything in their power to prevent the city from approving the creation of new units in previously rented space. The result is lower rents for one sitting tenant and much higher rents for the several tenants that otherwise could have lived at the upgraded property.
Most homeowners (and investors) do not realize how extremely frustrating it can be to have a city board that is not accountable to city council setting housing [anti] development policies. Larger more experienced landlords are harder for these agencies to tackle, so their focus over the past 10 years has increasingly shifted to 1-3 unit homeowner landlords.
I like Rob's ideas. In particular, there are thousands of unpermitted second units in many California cities. Some have policies that allow legalization of unpermitted ADUs. I routinely review all ADU permits filed in Oakland, which has marvelous public records act management systems in place. About 10% of the past thousand ADU permits include the word "legalization." So, even if their ordinance makes no mention of a legalization process, one exists and is in use.
While a hundred or more homeowners are pursuing legalization, there may be 10,000 unpermitted seconds in Oakland. A fairly high percentage of those owners might be losing sleep at night worrying about the fate of their "illegal" units. They may be aware that CMs Kalb and Kaplan and others have imposed harsh new restrictions on evictions and rent increases in owner occupied duplexes and triplexes. I think there are (or will soon be) a lot of concerned homeowner landlords in cities with rent boards. Anyway, my point is that if you know how to legalize unpermitted units as ADUs, and you know how to market to owners of unpermitted rental units, then there seems to be tens of thousands of opportunities in this untapped sector. If I knew when unpermitted properties had a vacancy, that would be the perfect instant to make a pitch. Informed buyers of properties with vacated unpermitted units can make those units legal and safe. An idea and not a recommendation.
So, it is kind of a race. Either the rent boards find the unpermitted rental and encourage the tenants to never move out, or an informed buyer purchases, corrects code violations and rents a safe unit. Only the rent boards know when one of the unpermitted units they've enabled to persist burns down.
I am interested in a deep discussion among interested peers of the particulars, implications and opportunities of California's SB 50. This Thursday's vote could help provide some certainty wrt its prospects for passage. I am in the East Bay.
