We''ve been extremely busy installing ADU's throughout San Diego County and the landscape is changing by the day. If you're in California I would recommend boning up on the latest HCD ADU laws and regs (https://www.hcd.ca.gov/policy-...). I'd also get up to date on all the recent FDMC/FNMA FHA laws, https://www.americanbanker.com... for manufactured housing which also applies to ADUs. https://sf.freddiemac.com/faqs... and https://appraisersblogs.com/fa...
A lot has changed in ADU land since the premier January, 2017 rollout of SB-1069 https://www.hcd.ca.gov/policy-... and it's a challenge trying to jump through all the hoops. The State is constantly updating and amending their law/s causing jurisdictions to change their ordinances about as often as we change our bed linens. With all these hoops to jump through it's even difficult for contractors, purveyors, architects and myriad stakeholders to follow the bouncing ball let alone pull permits in a timely manner.
Add to that the challenge of educating appraisers and you've got a hat trick that is keeping the entire ADU industry on its toes 24/7/365. For the turn and burn investor trying to throw up an ADU and sell to make a fast few it's not quite time. There just aren't that many ADU properties that have sold let alone even on the market yet. So good appraisals are a challenge until there's more ADU sales on the market. Now for the buy and hold type the ball is in your court. If you were prudent in building/installing your backyard home or you purchased a property with one already built out, time is on your side.
All is not bad, however, At the end of the day we find that about 50% of our clients are adding them to their property for a family member, home health care provider, domestic employee, etc. The other 50% are investors seeking additional revenue streams and ROI. Bottom line this once "cottage industry" is fast becoming a "major growth industry" very similar to the remodeling and fix and flip trends we saw in the post '08 meltdown. All in all there is very little downside risk compared to the long term upside potential depending on your investment criteria. Hope you find this useful.