According to this poll, the majority of ADUs are used as income-generating rentals (51%). Another 17% are used for friends or relatives staying there for free. 6% are being occupied by the owner of the property while they rent out the primary home. 7% needed construction before they could rent it. And 1% were vacancies between occupants.
Good article and I have lots of thoughts about what the housing movement can learn from ADUs. But it breaks my heart to see the author of Brave New Home citing 8 year old research and including Canada as the US' 51st state.
Interesting -- the stat of 40 percent of ADUs being used for something other than long-term rentals is the most widely cited, including by some major ADU advocates like AARP. I had no idea the data was so old and skewed.
That said, I have seen other data that often has figures that are similar or worse. For example, here is a 2020 research report on Los Angeles that is trying to understand how many ADUs are actually used for long-term rentals and finds that only 1/3 of ADU owners plan to use their ADUs just as a rental to strangers, 1/3 plan to house family, and 1/3 have no plans to rent at all. https://www.anderson.ucla.edu/documents/areas/ctr/ziman/2020-12WP.pdf
The data you share says that only 51 percent are income-generating rentals -- it's good, but not as good as rentals that are built to be rented, right? If half the multifamily rentals were never on the open market as rentals, we'd be in serious trouble. So if we're putting a lot of eggs in the basket of ADUs to solve an affordable housing problem, I think we're in trouble. If we're looking to them to solve other issues, like caregiving and social isolation, etc. that's a different question.
Regardless, I think we can agree that ADUs are great. But in my opinion, they've become the default for new housing stock. I'm really glad that new conversations about building code and small apartment buildings are also becoming mainstream and amplified as well.
I totally agree that ADUs should not solve our housing shortage all alone. They're just one typology. But we don't need to say that 40% are unoccupied and make it a big pull quote for our article about what we can learn from ADUs. Even if AARP did it first.
For context, we just had to fight off a legislative effort in the California State Assembly that wanted to let cities impose occupancy requirements (ie mandatory lease requirements for the first 10 years) on ADUs, so I'm kind of reeling over here. ;D
San Diego might not be the ADU paradise that some think it is. The city went wild with its bonus ADU program and now the backlash is both powerful and appropriate:
Another point I would like to raise concerns "single-family home." This is not news to you, but this is a planning concept, but arguably it existed as what we associate with an architectural form well before the advent of the planning era. What looks like a "single-family home" from its form was used as a boardinghouse or subleased and shared with another family. In that sense, "single-family home" is a social construction. Planning creates the associated legal construction, but there's a strong cultural component supporting it as well.
Great piece and thanks particularly for noting how many ADUs are not used as long term residences. In mainstream and YIMBY conversations this nuance is almost always glossed over. This wouldn't be so bad if not for California allowing all ADUs to count against RHNA requirements, at much lower price levels than even rented ones actually go for. In the expensive markets where entry level housing is needed most, ADUs that are home offices, gyms, and guest houses are being used as loophole to get out of the need to actually build more supply.
I should probably provide some context since this isn't a California specific platform. RHNA is Regional Housing Needs Allocation, is a requirement for jurisdictions across California to allow for housing production at various income levels. While the requirement has existed since 1969 it has been toothless which thankfully is changing through statewide legislation, particularly SB423. If jurisdictions fail to meet their allocation they can lose local control of discretionary approvals and even state funding, San Francisco has already lost some control as the bill put their first check in at 2024 instead of the rest of the state which will happen in 2026. Many cities that should lose their ability to keep turning down housing projects next year will be able to get out of it because of these additions masquerading as ADUs.
As a former city councilmember, I participated in the 4th and 5th 8-year RHNA cycles and have actively watched the 6th 8-year RHNA cycle. While I agree with Brian Cade on most of his points, I do want to make some corrections. SB 423 (2024) ,was an update I Sen. Wiener's earlier bill, SB 35 (2017). SB 423 extended the sunset date of the bill, made several other minor adjustments, and, after a big fight in Sacramento, did extend the bill to the California's Coastal Zone. In SB 423 Sen. Wiener did add an exception for San Francisco, where Wiener was on the Board of Supervisors before moving to the state senate. Under the bill, SF is evaluated annually, instead of every four years, the time period which applies to the remaining 539 jurisdictions in California. The RHNA 4-year midpoint will arrive at different years, mostly on June 30--2025 for San Diego County, 2026 for the six-county Southern California region and the six-county Sacramento region, and 2027 for the nine-county Bay Area region. These regions include more than 80 percent of California's population. The remaining counties have their own schedules. For a map see Figure Two in this report: https://information.auditor.ca.gov/reports/2021-125/index.html. The 6th cycle RNHA targets are so bloated and unrealistic that almost all of the states 540 jurisdictions (cities and counties) will fail to meet their targets. The result was guaranteed by the Wiener bill SB 828 (2018) which was sponsored by the Bay Area Council and the Silicon Valley Leadership Group. The bill deliberately set up absurd targets that set up cities to fail, which will trigger streamlined ministerial (rubber stamp) approval processes. ADUs won't matter expect in a few jurisdictions.
Thanks for sharing this piece and highlighting this trend. I can definitely see how this might be part of the solution to the housing crisis — increasing supply while preserving community character and avoiding the usual “NIMBY” resistance.
I’ve worked in residential development for years and in the construction industry for over two decades, and I’m convinced there’s enormous untapped potential to boost supply simply by being smarter. That’s exactly what I’ve started writing about.
Soon, once I’ve covered the key challenges, I’ll begin exploring solutions — and this will certainly be one of them. If it’s alright with you, I’d love to reference your work and perspective.
"estimated 40 percent of ADUs in the U.S." based on a poll of 255 people in VANCOUVER, Seattle, and Portland from 2017.
2021 poll with similar methodology, focused on California, finds 82% are occupied or required further work before they could be occupied. https://www.aducalifornia.org/wp-content/uploads/2021/04/Implementing-the-Backyard-Revolution.pdf
According to this poll, the majority of ADUs are used as income-generating rentals (51%). Another 17% are used for friends or relatives staying there for free. 6% are being occupied by the owner of the property while they rent out the primary home. 7% needed construction before they could rent it. And 1% were vacancies between occupants.
Good article and I have lots of thoughts about what the housing movement can learn from ADUs. But it breaks my heart to see the author of Brave New Home citing 8 year old research and including Canada as the US' 51st state.
Interesting -- the stat of 40 percent of ADUs being used for something other than long-term rentals is the most widely cited, including by some major ADU advocates like AARP. I had no idea the data was so old and skewed.
That said, I have seen other data that often has figures that are similar or worse. For example, here is a 2020 research report on Los Angeles that is trying to understand how many ADUs are actually used for long-term rentals and finds that only 1/3 of ADU owners plan to use their ADUs just as a rental to strangers, 1/3 plan to house family, and 1/3 have no plans to rent at all. https://www.anderson.ucla.edu/documents/areas/ctr/ziman/2020-12WP.pdf
The data you share says that only 51 percent are income-generating rentals -- it's good, but not as good as rentals that are built to be rented, right? If half the multifamily rentals were never on the open market as rentals, we'd be in serious trouble. So if we're putting a lot of eggs in the basket of ADUs to solve an affordable housing problem, I think we're in trouble. If we're looking to them to solve other issues, like caregiving and social isolation, etc. that's a different question.
Regardless, I think we can agree that ADUs are great. But in my opinion, they've become the default for new housing stock. I'm really glad that new conversations about building code and small apartment buildings are also becoming mainstream and amplified as well.
I totally agree that ADUs should not solve our housing shortage all alone. They're just one typology. But we don't need to say that 40% are unoccupied and make it a big pull quote for our article about what we can learn from ADUs. Even if AARP did it first.
For context, we just had to fight off a legislative effort in the California State Assembly that wanted to let cities impose occupancy requirements (ie mandatory lease requirements for the first 10 years) on ADUs, so I'm kind of reeling over here. ;D
San Diego might not be the ADU paradise that some think it is. The city went wild with its bonus ADU program and now the backlash is both powerful and appropriate:
https://obrag.org/2025/04/clairemont-realtor-showcases-high-density-projects/
Another point I would like to raise concerns "single-family home." This is not news to you, but this is a planning concept, but arguably it existed as what we associate with an architectural form well before the advent of the planning era. What looks like a "single-family home" from its form was used as a boardinghouse or subleased and shared with another family. In that sense, "single-family home" is a social construction. Planning creates the associated legal construction, but there's a strong cultural component supporting it as well.
Great piece and thanks particularly for noting how many ADUs are not used as long term residences. In mainstream and YIMBY conversations this nuance is almost always glossed over. This wouldn't be so bad if not for California allowing all ADUs to count against RHNA requirements, at much lower price levels than even rented ones actually go for. In the expensive markets where entry level housing is needed most, ADUs that are home offices, gyms, and guest houses are being used as loophole to get out of the need to actually build more supply.
Such a good point! I didn’t even know about that California example. Thanks for sharing!
Thanks Diana!
I should probably provide some context since this isn't a California specific platform. RHNA is Regional Housing Needs Allocation, is a requirement for jurisdictions across California to allow for housing production at various income levels. While the requirement has existed since 1969 it has been toothless which thankfully is changing through statewide legislation, particularly SB423. If jurisdictions fail to meet their allocation they can lose local control of discretionary approvals and even state funding, San Francisco has already lost some control as the bill put their first check in at 2024 instead of the rest of the state which will happen in 2026. Many cities that should lose their ability to keep turning down housing projects next year will be able to get out of it because of these additions masquerading as ADUs.
As a former city councilmember, I participated in the 4th and 5th 8-year RHNA cycles and have actively watched the 6th 8-year RHNA cycle. While I agree with Brian Cade on most of his points, I do want to make some corrections. SB 423 (2024) ,was an update I Sen. Wiener's earlier bill, SB 35 (2017). SB 423 extended the sunset date of the bill, made several other minor adjustments, and, after a big fight in Sacramento, did extend the bill to the California's Coastal Zone. In SB 423 Sen. Wiener did add an exception for San Francisco, where Wiener was on the Board of Supervisors before moving to the state senate. Under the bill, SF is evaluated annually, instead of every four years, the time period which applies to the remaining 539 jurisdictions in California. The RHNA 4-year midpoint will arrive at different years, mostly on June 30--2025 for San Diego County, 2026 for the six-county Southern California region and the six-county Sacramento region, and 2027 for the nine-county Bay Area region. These regions include more than 80 percent of California's population. The remaining counties have their own schedules. For a map see Figure Two in this report: https://information.auditor.ca.gov/reports/2021-125/index.html. The 6th cycle RNHA targets are so bloated and unrealistic that almost all of the states 540 jurisdictions (cities and counties) will fail to meet their targets. The result was guaranteed by the Wiener bill SB 828 (2018) which was sponsored by the Bay Area Council and the Silicon Valley Leadership Group. The bill deliberately set up absurd targets that set up cities to fail, which will trigger streamlined ministerial (rubber stamp) approval processes. ADUs won't matter expect in a few jurisdictions.
Dear Diana,
Thanks for sharing this piece and highlighting this trend. I can definitely see how this might be part of the solution to the housing crisis — increasing supply while preserving community character and avoiding the usual “NIMBY” resistance.
I’ve worked in residential development for years and in the construction industry for over two decades, and I’m convinced there’s enormous untapped potential to boost supply simply by being smarter. That’s exactly what I’ve started writing about.
Soon, once I’ve covered the key challenges, I’ll begin exploring solutions — and this will certainly be one of them. If it’s alright with you, I’d love to reference your work and perspective.
Cheers,
Torstein 🫡
Always love to be referenced! Thanks for the feedback!