1/28/26
1 DISCLAIMER:
This memo provides a technical overview of the ADU Affordability Survey and its potential implications for affordability designations in Annual Progress Reports (APRs). It does not constitute legal advice.
This memo was published
in
January
202
6 .
ADU Affordability Survey Findings
and Recommendations
Executive Summary
In partnership with
Bay Area
jurisdiction
s
,
the Association of Bay Area Governments (ABAG)
has been
administering an
affordability survey
to learn more about the rents of newly built ADUs
.
In 2024 and 2025,
p
articipating jurisdiction
s
distribute
d
the survey as part of the permitting process
.
This data is complimented
by similar studies in Oakland and San Jos
é
.
Based on the results of the survey
s
, the
California Department of Housing and Community Development (HCD)
is comfortable with ABAG
jurisdictions
continuing to use the following ass
umptions
in their Annual
Progress Reports
(APRs)
for
two
more
years (APR 2025 and 2026)
:
•
30% very low income
•
30% low income
•
30%
moderate income
•
10% above moderate income
Please read this memo for more information.
History
In 2021, ABAG, in partnership with UC Berkeley, conducted an ADU affordability study to inform affordability assumptions for Housing Element APR reporting. HCD endorsed the findings of this initial study, and most jurisdictions have since
used
the
30/30/30/10 affordability split
in their Housing Elements and APRs
.
Building on the 2021 study, ABAG’s Regional Housing Technical Assistance (RHTA) program launched a
regional, opt
-
in ADU affordability survey to collect information from homeowners during the ADU approval process. The survey support
s
jurisdictions in documenting the affordability of newly constructed ADUs and in ATTACHMENT 2
1/28/26
2 meeting Housing Element monitoring requirements. Developed in consultation with an advisory group of jurisdiction staff and reviewed by HCD, the survey was initially launched in 2024 and revised in 2025. The survey remains active, with additional analysis
anticipated as more responses are collected.
2024
-
2025 Survey and Data Overview
To date, at least 39 jurisdictions have implemented the survey.
Some
require
homeowners to
fill it out
during
the
ADU building permit process
, while others
encourage
them to do so
.
The survey takes approximately
five
minutes to complete and asks general questions about
the ADU the
homeowner intends to build
such as
type
(e.g. detached)
, s
quare footage, bedroom count,
expected
inhabitants
(e.g. renters, family, friends)
and
anticipated rent.
To encourage accurate responses and protect
privacy, the survey is anonymous. Because rent information can be sensitive, the survey collects anticipated rent using ranges rather than exact amounts.
Between July 2024 and September 2025, the survey received 436 responses
. To supplement these, two
additional datasets were incorporated:
•
City of Oakland Survey:
142 responses,
(
2025
)
focused on existing ADUs
.
•
City of San José Survey:
79 responses
(2024 and 2025)
, based on the ABAG survey with minor
modifications
.
This resulted in a combined dataset of
657 total responses
, representing
39 jurisdictions
in the ABAG region
.
Alameda County had the largest share (31%), followed by Santa Clara County (23%) and Contra Costa County (17%)
.
County
Percent of Total
Alameda (including
the
Oak
l
and survey)
31%
Contra Costa
17%
Marin
3%
Napa
1%
San Francisco
5%
San Mateo
14%
Santa Clara (including
the
San
José
survey)
23%
Solano
2%
Sonoma
4%
ATTACHMENT 2
1/28/26
3 2024
and 2025 Initial
Results
ABAG discussed survey findings with HCD in December 2025. Based on these discussions and additional analysis, HCD endorsed the continued use of the 30/30/30/10 affordability split for typical ABAG jurisdictions for APR reporting
for two more years (APR 2025 and 2026)
. Jurisdictions may still submit alternative data to
HCD if they believe it supports a different affordability distribution. As in prior years, while the 30/30/30/10 assumptions are appropriate for most jurisdictions, HCD may request additional information
in select
circumstances.
Affordability analysis of survey data collected between July 2024 and September 2025 , summarized below,
supports the continued use of the 30/30/30/10
affordability
assumptions
.
Affordability Level
Affordability Based on
Survey
Responses
Recommendation
E
xtremely
L
ow
I
ncome
and
V
ery
L
ow
I
ncome
57%
30%
L
ow
I
ncome
30%
30%
M
oderate Income
11%
30%
Above
M
oderate Income
1%
10%
Although the survey results suggest deeper affordability than assumed under the 30/30/30/10 framework, ABAG recommends maintaining the current split for the following reasons:
•
Less than two full years of survey data are
available
.
•
The dataset relies heavily on proposed (rather than occupied) ADUs, which may involve less precise rent estimates
.
•
While meaningful, the overall sample size remains relatively modest .
Continued jurisdiction participation and active promotion of the ADU affordability survey will strengthen the dataset over time and support more refined affordability assumptions in future APR cycles.
C
ontact Hannah Diaz
,
with questions or comments about the survey
.
ATTACHMENT 2
1/28/26
4 Appendix
Data Filtration
Since the goal of the analysis
is to estimate the affordability levels of proposed ADUs
(
and existing ADUs in the
case of the Oakland data
)
several response types were
removed to avoid skewing results:
•
R
esponses indicating the ADU would not be used for housing ;
•
Responses from
the original ABAG Survey
with “0” listed as expected ren
t;
•
Responses selecting “
d
ecline to
s
tate”
for rent amount
on the updated
ABAG
survey
; and
•
Responses designated as “rent not shared” on the Oakland Survey.
After applying these
filters,
460 responses
remained with adequate rent data for affordability analysis.
Affordability Methodology
The following describes the data standardization and methodology applied to determine the affordability level of the proposed (or existing) ADU. The methodology considers the year the ADU was proposed, the county it is permitted in
, and the bedroom
count
.
Calculating Affordability
In order to determine the affordability of the ADU, a formula was developed
based on HCD’s
State Income
Limits
. The formula is based on the
year
-
specific
c
ounty
m
edian
i
ncome and then adjusted for both occupancy
and income category.
The following household size assumptions were used depending on the bedroom count of the ADU:
•
Studio:
one
-
person household, 70% of
c
ounty
m
edian
i
ncome
;
•
One
Bedroom
:
two
-
person household, 80% of the
c
ounty
m
edian
i
ncome
;
•
Two
Bedroom:
three
-
person household, 90% of the
c
ounty
m
edian
i
ncome
; and
•
Three
Bedroom:
four
-
person household,
c
ounty
m
edian
i
ncome.
ATTACHMENT 2
1/28/26
5 Once the
county median
incomes were adjusted
for household size,
then thresholds for income levels were
established as follows:
•
Extremely Low Income:
Up to 30% of the adjusted
c
ounty
-
specific
m
edian
i
ncome
;
•
Very Low Income:
between 31% and 50% of the adjusted
c
ounty
-
specific
m
edian
i
ncome
;
•
Low Income
: between 51% and 80% of adjusted
c
ounty
-
specific
m
edian
i
ncome
; and
•
Moderate Income:
between 81% and 120% of adjusted
c
ounty
-
specific
m
edian
i
ncome
.
Rent Thresholds
From the adjusted incomes, a maximum monthly rent
threshold and range
was established using the
assumption that occupants should only spend up to 30% of their income on housing.
Example:
The 2024
m
edian
i
ncome in Alameda County was $155,700. To
calculate the maximum rent for a
one bedroom,
e
xtremely
-
l
ow
-
i
ncome ADU household, first adjust the median income for expected occupancy (
two
persons, therefore 80% of the
m
edian Income) which is $124,560. Then adjust for the
e
xtremely
-
l
ow
-
i
ncome
c
ategory to calculate the maximum yearly income to qualify as e
xtremely
l
ow
i
ncome (ELI is up to 30%
of the
m
edian Income) which is $37,368. Lastly, calculate the maximum monthly rent ( r
ent maximum is 30%
of annual income) which is $934 a month. ($37,368 x 0.3 / 12
months)
Categorization
The survey responses were categorized first by calendar year since the income limits are updated yearly, and then by location, since each county has its own calculated median income.
Since
the second version
of the survey asks respondents to choose a range for their intended rent, the analysis uses
an even distribution to assign affordability which preserves proportionality .
Example:
If
l
ow
i
ncome
maximum rent is $15 per month, and 10 people choose the box "between $10 and $20 a month" for rent,
five
units would be
considered low
-
income units
and
five
units would be moderate
income
units.
ATTACHMENT 2
1/28/26
6 Updates to the Survey Questions to Improve Rent Data Accuracy
An issue identified from
the first version
of the survey (open from
July
2024
to February 2025) was that the
rent question was open
-
ended, asking respondents to write the amount that they intend ed
to charge for
monthly rent of the ADU. The question explicitly stated that writing a “0” meant that homeowner did
not
intend to charge rent.
The findings from
the first survey
showed that a high percentage of respondents were giving an answer of “0” when asked about the expected rent of their proposed ADU, which led to the concern that respondents were potentially
not
providing an accurate rent estimate or intend
ed
to charge zero rent for their units. This
difference has important implications for calculating affordability, since a unit that has zero rent would be considered “extremely low income.”
To address this concern, the rent question was updated in the second version of the survey
(open from
February 2025 onward) to a multiple
-
choice response which included a “decline to state” option, a “not planning to charge rent” option, and then rent ranges (for example $1,500 –
$2,000).
ATTACHMENT 2