Twelve working tools for a project most people only do once. Each shows its arithmetic, names its sources, and gives the answer on screen — none asks for an email first.
HyreADU does not design, permit or build ADUs, and takes no referral fee, which is why these can tell you the numbers do not work.
41%of permitted ADU units with no matching completion46,944 of 114,651 units permitted 2018–2023, following each permit year forward in California’s own Annual Progress Report. A HyreADU calculation on California Department of Housing and Community Development, Housing Element Annual Progress Report, Table A2. Approval is the cheap half.
Start with the stage you are at.
Is it allowed? The feasibility checker and size envelope give you the questions for the planning counter, not an answer about your parcel.
What does it cost? The cost, financing, ROI and rent tools do the arithmetic on your numbers, because we publish no national ADU price.
In California, replacing garage parking is largely off the table: Gov. Code § 66314(d)(11) says a converted or demolished garage “shall not require that those offstreet parking spaces be replaced.” What stops projects is further downstream: the utility connection charge, which Gov. Code § 66311.5 does not waive, and the financing.
Pick your stage
Every tool, by where you are
1
Is this even allowed here?
Start here, and start before you pay anyone for drawings. These pages produce the questions to take to the planning counter — not an answer about your lot, which no website can give you.
We ship no national ADU price. These pages do arithmetic on line items you type in, and put the published third-party figures beside your numbers rather than in place of them.
A permit is not a unit, and California’s own reporting says so
The number everybody quotes is the permit count. It is the wrong number. The state publishes both columns, and the gap between them is the most important fact on this site.
Both columns are the state’s own. Across 2018-2025, 178,495 ADU building permits and 102,356 completions were reported — a cumulative ratio of 57%.California Department of Housing and Community Development, Housing Element Annual Progress Report, Table A2. HyreADU calculation on Table A2.
The headline figures. California Department of Housing and Community Development, Housing Element Annual Progress Report, Table A2 publishes Table A2 of the Housing Element Annual Progress Report. Across 2018-2025 it carries 281,321 ADU rows from 511 jurisdictions: 178,495 permitted units against 102,356 completions.
Follow the cohort rather than the year. Comparing this year’s permits with this year’s completions is meaningless, because the two describe different buildings.
Following each permit year forward is the honest cut, and it gives 41% of ADU permit units issued between 2018 and 2023 — 46,944 of 114,651 — with no matching completion in the file.
That is a HyreADU calculation on the state’s dataset, and the method is on the research page.
Read that carefully before you use it. These are reported APR rows, not a physical census of construction.
An unmatched permit may be a unit still under construction, an abandoned project, a unit completed without a reported certificate, or a project whose identifier changed between the permit row and the completion row.
The direction is robust; the exact rate is a reporting artefact as much as a construction one.
Where the completions that do land, land. Among matched projects the median lag is 1 year: 29% complete in the permit year, 79% within one year, 94% within two. So a project that has not reported a completion three years after its permit is not usually still in progress. Something stopped it.
Why this belongs at the top of a page of calculators. Every tool here produces a number, and a number is persuasive.
The unmatched share is the standing reminder that a large minority of people who got as far as a building permit — drawings paid for, fees paid, approval in hand — did not end up with a building.
The tools are most useful in finding out, early and cheaply, whether you are one of them.
In California, the objection you are bracing for has been legislated away
People arrive at this expecting a fight about parking and about whether they will be allowed to rent it out. In California, most of that fight has already been had, in the Legislature, and the homeowner won it.
First, cite it correctly. SB 477 (Stats. 2024, ch. 7), an urgency measure effective 25 March 2024, recodified State ADU Law out of Government Code § 65852.2 into Chapter 13 of Division 1 of Title 7, sections 66310 through 66342.
A guide that still cites § 65852.2 is citing a repealed numbering. State ADU law now sits at Gov. Code §§ 66310–66342.
This is a genuinely useful test of a source: a guide, a consultant or a planning handout still working from § 65852.2 has not been revised since March 2024, and ADU law has moved twice since.
The parking objection is prohibited outright. Gov. Code § 66314(d)(11): "When a garage, carport, covered parking structure, or uncovered parking space is demolished in conjunction with the construction of an accessory dwelling unit or converted to an accessory dwelling unit, the local agency shall not require that those offstreet parking spaces be replaced." And where parking is required at all, Gov. Code § 66314(d)(10)(A) caps it: "Parking requirements for accessory dwelling units shall not exceed one parking space per accessory dwelling unit or per bedroom, whichever is less. These spaces may be provided as tandem parking on a driveway." Under § 66314(e) a demolition permit for a detached garage being replaced by an ADU is reviewed with the ADU application and issued at the same time, and under § 66314(f) no written notice or placard is required for that demolition unless the property is in a historic district.
So is the owner-occupancy requirement. Gov. Code § 66315, added by SB 477 (Stats. 2024, ch. 7), effective 25 March 2024, in full: "Section 66314 establishes the maximum standards that a local agency shall use to evaluate a proposed accessory dwelling unit on a lot that includes a proposed or existing single-family dwelling. No additional standards, other than those provided in Section 66314, shall be used or imposed, including an owner-occupant requirement, except that a local agency may require that the property may be used for rentals of terms 30 days or longer." One honest caveat: We looked for a sunset or expiry on that prohibition and did not find one, and we did not retrieve the separate JADU article (§§ 66333 and following), which has its own owner-occupancy treatment. Do not read this as covering a JADU.
And there is no hearing. Gov. Code § 66317(a)(1): "A permit application for an accessory dwelling unit shall be considered and approved ministerially without discretionary review or a hearing, notwithstanding Section 65901 or 65906 or any local ordinance regulating the issuance of variances or special use permits." Under Gov. Code § 66317(c), "No local ordinance, policy, or regulation, other than an accessory dwelling unit ordinance consistent with this article shall be the basis for the delay or denial of a building permit".
Nor can the ADU drag fire sprinklers into the existing house. Gov. Code § 66314(d)(12): "Accessory dwelling units shall not be required to provide fire sprinklers if they are not required for the primary residence. The construction of an accessory dwelling unit shall not trigger a requirement for fire sprinklers to be installed in the existing primary dwelling." And under Gov. Code § 66323(a), "A local agency shall not require, as a condition for ministerial approval of a permit application for the creation of an accessory dwelling unit or a junior accessory dwelling unit, the correction of nonconforming zoning conditions."
The decision is ministerial and it is on a clock. Under Gov. Code § 66317(a)(3), as amended by SB 543 (Stats. 2025, ch. 520, effective 1 January 2026), the permitting agency "The permitting agency shall either approve or deny the application to create or serve an accessory dwelling unit within 60 days from the date the permitting agency receives a completed application if there is an existing single-family or multifamily dwelling on the lot." And if it does not: If the local agency has not approved or denied the completed application within 60 days, the application is deemed approved.
If the applicant requests a delay, the 60 days are tolled for the length of the delay.
There is now a completeness clock too. SB 543 added a completeness clock: a written completeness determination within 15 business days, a list of what is missing, a limited resubmittal, and a deemed-complete consequence if the agency misses the determination.
An appeal of incompleteness or of a denial gets a final written determination within 60 business days (§ 66317(d)). Those are business days; the 60-day decision is not labeled as business days.
Impact fees have a hard floor. Under Gov. Code § 66311.5 — and note The ADU fee rules that used to sit in former § 65852.2, and then at § 66324, were renumbered to § 66311.5 by SB 543 (Stats. 2025, ch. 520, effective 1 January 2026). — Impact fees may not be imposed on an ADU of 750 square feet of interior livable space or less (or a JADU of 500 or less).
Above 750 square feet, impact fees must be proportional to those for the primary dwelling. School developer fees under Education Code § 17620 are a different statute.
Section 66311.5(c)(3) treats an ADU or JADU under 500 square feet of interior livable space as not increasing assessable space by 500 square feet.
A unit at 749 square feet of interior livable space and a unit at 751 can differ by five figures of park, traffic and school charges before anyone lifts a hammer.
But the connection charge is not an impact fee. Connection and capacity charges are NOT impact fees.
Under § 66311.5(b), an ADU is not a new residential use for connection-fee purposes unless it is built together with a new single-family dwelling — but the utility can still bill a connection or capacity charge, and that bill is outside the impact-fee prohibition entirely.
This is the single most common unpleasant surprise in an ADU budget: the fee prohibition people have read about does not reach the bill that arrives from the water and power utility, and that bill can be large enough to change the project.
And on the coast, a formerly open-ended process is now timed. A local government with a certified local coastal program must approve or deny a coastal development permit for an ADU within 60 days of a completed application, concurrently with the § 66317 decision, without a public hearing, and not subject to appeal under Public Resources Code § 30603.
Where there is no certified LCP the Coastal Commission carries the same 60-day duty, with a deemed-approved consequence if it misses.
That is Gov. Code § 66329, AB 462 (Stats. 2025, ch. 491, effective 10 October 2025).
What this adds up to. The reflex assumption — that the city will find a way to say no — is now, in California, usually wrong, and the reflex is expensive because it stops people asking. What stops ADUs is further downstream: the money, and the utility.
All nine, and the question each one actually answers
The third column is the useful one. Every tool has a boundary, and knowing where it sits saves you asking it something it cannot answer.
Tell you your lot qualifies. Parcel-level feasibility turns on easements, utilities, soils, fire zones and overlays that no website can see. It produces questions, not permission.
Ship a national or state average as your budget. We hold no dataset of ADU bids, and the third-party medians on this site are dated, labeled and someone else’s.
How long until rent covers the build, on my assumptions?
Model tax, depreciation, vacancy risk properly, or discount future cash flows. It is deliberately simple and says so, because a false precision here is worse than none.
Invent your area’s number, or tell you what your unit will let for. FMR is a 40th-percentile policy construct including utilities — not observed ADU asking rent.
How long is each phase, and which one do I not control?
Give you a completion date. Permit review is not a duration you can plan around; the observed distributions on this site are wide enough to make that obvious.
Are these three bids describing the same building?
Tell you a price is too high. It tests whether the documents can be compared at all, which correlates with what you care about better than price does.
The 60-day clock, and the 162-day and 445-day realities
The statute is real. So are the observed durations. Understanding why they differ is more useful than either number alone, and it tells you exactly where your own project will lose time.
Not a compliance finding. The statute runs from a COMPLETED application; these medians run from the published submitted, filed or received date.LADBS Building and Safety — Building Permits Issued from 2020 to Present (N); DataSF Building Permits (DBI Permit Tracking System extract); Marin County Community Development Agency — Building Permit (mkbn-caye). Retrieved 2026-09-05.
The observed distributions. Los Angeles: median 162 calendar days across 27,188 non-supplemental ADU building permits, interquartile range 79–301, with 19% taking more than a year. Unincorporated Marin: median 174.5 across 472. San Francisco: median 445 across 1,713 unique issued permits, IQR 276–707, and 62% over a year.
Why this is not a finding that anyone broke the law. These are calendar days from the published application-side date to issuance, on permits that issued.
The statutory 60 days runs from a COMPLETED application, and none of the three extracts marks the completeness determination.
The gap between the two therefore includes every day an applicant spent curing an incomplete set, paying fees, answering plan-check comments, or asking for delay.
A median above 60 days is not, by itself, a finding that a city missed the shot clock.
Which is exactly why it is useful to you. If the gap between 60 days and 162 is mostly time spent curing an incomplete application, answering plan-check comments and paying fees, then it is largely time your team controls.
The most valuable thing a designer does for an ADU project may be submitting a set complete enough that the clock actually starts.
Two jurisdictions are missing, and that is a finding too. City of Sacramento: The published issued-permit layer has Status_Date (the issued/status date) and Application as a permit number (e.g. RES-2600002). No application/filed/submitted date field is published. Duration cannot be computed.
City of San José: CKAN resources publish ISSUEDATE and FINALDATE. No application, filed, received or submitted date. Duration cannot be computed. Neither publishes an application-side date, so no duration can be computed. We would rather say so than substitute a proxy.
And there is a faster statutory route almost nobody uses. Under Cal. Gov. Code § 65852.27 (AB 1332 (Carrillo, 2023), effective 2025-01-01), A complete application for a DETACHED ADU that uses a plan preapproved in the current triennial California Building Standards Code cycle, or a plan identical to one the agency already approved in that cycle, must be approved or denied ministerially within 30 days.
By its terms that clock does not reach attached ADUs, garage conversions or JADUs unless a local program separately covers them. What catalogs actually exist is a separate question, covered on the pre-approved plans research page.
Four dollar figures that are constantly mistaken for each other
Each of these is a real, published number. None of them is the price of your ADU, and the last column is why.
The figure
What it actually is
Where it comes from
Why it is not your budget
$40,000 — Los Angeles median declared permit valuation
The number an applicant wrote on a permit form so the city could compute a fee.
HyreADU calculation on 3,809 nested permit valuations in the LADBS legacy contractor extract, owner-builder records excluded, zeros dropped.
Declared permit valuation is what an applicant writes on a form so a city can compute a fee. It is not a construction cost, it is not a bid, and it is not what the job was sold for. Where a fee scales with the number written down, the number written down has an obvious direction of error.
$150,000 — the 2021 owner-survey median
The median all-in cost reported by California ADU owners who had actually built one.
Chapple, Ganetsos and Lopez, Implementing the Backyard Revolution: Perspectives of California’s ADU Owners, UC Berkeley Center for Community Innovation, 22 April 2021
A real measurement of real projects — five years ago. 37% of that sample came in under $100,000 and 71% under $200,000, which tells you the spread is enormous and a median is a weak guide to any one project.
$230,351 — the same survey, indexed forward
The 2021 statewide median multiplied by 1.54, the ratio of the construction cost index between December 2019 and August 2026.
HyreADU arithmetic on DGS California Construction Cost Index, ENR Building Cost Index average of Los Angeles and San Francisco. HyreADU arithmetic on published indices applied to Chapple, Ganetsos and Lopez 2021 medians. Not a 2026 owner survey and not a bid.
The publisher of the index says plainly: "The ENR BCI reports cost trends for specific construction trade labor and materials in the California market and does not reflect current market bidding environment." An index adjusts a past number for input costs. It does not turn a 2021 survey into a 2026 quote.
$138,211 vs $276,421 — conversion against detached
The same indexation applied to the survey’s garage-conversion and detached-new-build medians.
Same source and same arithmetic as the row above.
The direction is the durable finding, not the amounts. A conversion reuses a slab, walls and a roof, and still pays for insulation, egress, a wet room, electrical service and whatever the garage was previously doing. Garage-conversion dollars belong on HyreGarage; this site does not price them.
Declared permit valuation, not construction cost. HyreADU calculation from municipal harvests. We hold no dataset of ADU bids, quotes or contracts. Every dollar figure on this site is a named third party’s published figure, arithmetic we performed on one and have labeled as ours, or a number you typed in.
The three things that actually stop an ADU
Not the planning department. Our reading of the evidence on this site is that the binding constraint has moved, and most advice has not moved with it.
Financing, first and mostly
An ADU is an expensive, illiquid improvement to a property that already carries a mortgage, and it produces no income until it is finished.
That is a hard shape to lend against, and the routes that exist — cash, home equity, a construction loan, a cash-out refinance — each have a reason they do not fit some households.
This is analysis rather than a source’s statement, and it is worth labeling as such. But it is consistent with the completion gap above: the projects that stop, stop after approval, which is the point at which somebody has to actually produce the money. The financing landscape study is the longer version.
The utility connection, second
Connection and capacity charges are NOT impact fees. Under § 66311.5(b), an ADU is not a new residential use for connection-fee purposes unless it is built together with a new single-family dwelling — but the utility can still bill a connection or capacity charge, and that bill is outside the impact-fee prohibition entirely.
So the sequence that catches people is this: they read that impact fees are barred below 750 square feet, they budget accordingly, and then the water district and the electricity utility each send a capacity or connection charge that the prohibition never touched.
Ask both utilities for a written figure before you commit, and ask specifically whether the existing service is adequate or must be upsized — an upsize is a different order of number.
The fee cliff, third and avoidably
Impact fees may not be imposed on an ADU of 750 square feet of interior livable space or less (or a JADU of 500 or less). Above 750 square feet, impact fees must be proportional to those for the primary dwelling.
A unit at 749 square feet of interior livable space and a unit at 751 can differ by five figures of park, traffic and school charges before anyone lifts a hammer.
Which makes 750 square feet of interior livable space the single most consequential dimension in the whole project, and it is a dimension a designer can hit deliberately. A unit drawn at 780 square feet because it looked balanced on a page is an expensive aesthetic decision that nobody flagged as a decision.
What is NOT usually the constraint
Discretionary review. In California, an ADU decision on a lot with an existing dwelling is ministerial and clocked under Gov. Code § 66317(a)(3): no hearing, no neighbor vote, and deemed approval if the agency misses. Even the coastal permit, historically the longest pole, now carries a concurrent 60-day duty without a public hearing.
None of which means your particular parcel is straightforward. It means the obstacle you expect is probably not the one you will meet, and budgeting anxiety against the wrong obstacle is how people end up in the unmatched share.
What Fair Market Rent is, and what it is not
Every ROI calculation on this site depends on a rent figure, so it is worth being precise about the only published benchmark most people can get to.
About half. 51% of surveyed owners reported the unit generating rental income; 16% reported housing a relative at no cost.Chapple, Ganetsos and Lopez, Implementing the Backyard Revolution: Perspectives of California's ADU Owners, UC Berkeley Center for Community Innovation, 22 April 2021
What FMR is. FMR is a 40th-percentile policy construct (gross rent including utilities) used for Housing Choice Vouchers. It is not observed ADU asking rent and not ACS median gross rent.
It is published by HUD Office of Policy Development and Research through the HUD Fair Market Rent Documentation System; the FY2026 figures took effect 2025-10-01.
What that means for your arithmetic. A 40th-percentile figure sits below the middle of the market by construction, and it includes utilities. If your ADU is let with utilities separate, the comparable number is lower than the FMR, not higher.
Using FMR as an asking rent quietly overstates the return, and using it as a floor quietly understates it. It is a benchmark, and it should be labeled as one in your own spreadsheet.
Why we make you look it up. HUD publishes FMR by metropolitan area and, in several metros, by ZIP as a Small Area FMR for the voucher program.
Baking one metro’s number into a calculator as a default would be a fake localiser: it would produce a confident figure for a reader in an area it does not describe.
The rent estimator therefore sends you to HUD’s own documentation system and does arithmetic on what you find there.
And half of these units are not let at market at all. In the 2021 owner survey, 51% generated rental income and 16% housed a relative at no cost.
That second group did not build a bad investment; they built a different thing, and an ROI calculation is the wrong instrument for judging it.
If the unit is for a parent, a returning adult child or a carer, the honest financial question is what the alternative arrangement would have cost — not what a tenant would pay.
What to ask, and when to ask it
In order. Each of these is cheap to ask and expensive to discover late, and the first four cost nothing at all.
Ask both utilities for a written connection or capacity figure — before you buy drawings
Water, sewer and electricity, separately, in writing, with the question "is the existing service adequate or must it be upsized". This is the number the fee prohibition does not reach, and it is the one most likely to change whether the project happens.
Ask the planning counter which code numbering they are working from
State ADU law is at Gov. Code §§ 66310–66342. A handout still citing § 65852.2 has not been revised since March 2024. This is not a gotcha — it is a fast way to find out how current the guidance you are being given is.
Decide the 750 square foot question deliberately
Impact fees may not be imposed on an ADU of 750 square feet of interior livable space or less (or a JADU of 500 or less).
Above 750 square feet, impact fees must be proportional to those for the primary dwelling.
If your design is drifting just over that line, make it an explicit trade against a five-figure fee rather than a drawing decision nobody costed.
Ask whether your jurisdiction has a pre-approved plan program
AB 1332 (Carrillo, 2023) required every local agency to develop one by 2025-01-01, and a detached ADU using a current-cycle pre-approved plan carries a 30-day decision. Whether your agency actually has a usable catalog is a separate question, and worth asking directly.
Get site work and utilities as priced lines in every bid
Not as an allowance, not as "by others", not as a note. Three bids that treat them differently are not three prices for one building, and the cheapest of them is usually just the shortest.
Do not assume the financing will be there because the approval is
Two in five permitted units in the 2018-2025 cohort have no matching completion. Approval is the cheap half. Arrange the money before you spend the fees, not after.
Do not take anything on this page as legal advice about your parcel
Statutes are quoted here at the numbering current on the retrieval date and they change every session. Local implementation, overlays, coastal zones, fire severity zones and easements all sit on top. The planning counter is free; use it early.
The vocabulary, once
Terms that appear across several of these tools, with the meanings they actually carry.
ADU
An accessory dwelling unit: an independent living facility on a lot with an existing or proposed primary dwelling, with its own kitchen, bathroom and entrance.
JADU
A junior accessory dwelling unit — smaller, carved out within the walls of the existing house. It has its own statutory treatment, including a parallel decision clock at Gov. Code § 66335, and its own fee threshold at 500 square feet.
Ministerial approval
A decision made against objective standards with no discretion and no hearing. Under Gov. Code § 66317(a)(3) an ADU application on a lot with an existing dwelling is ministerial, clocked at 60 days from completeness, and deemed approved if the agency misses.
Completed application
The point at which the statutory clock starts — not the day you submitted. SB 543 added a completeness clock: a written completeness determination within 15 business days, a list of what is missing, a limited resubmittal, and a deemed-complete consequence if the agency misses the determination.
Interior livable space
The measurement the fee thresholds turn on. 750 square feet of it is the impact-fee cliff; 500 is the school-fee threshold. It is not the same as gross area, and the difference can be the whole decision.
Impact fee
A charge for the burden new development places on public facilities — parks, traffic, schools. Impact fees may not be imposed on an ADU of 750 square feet of interior livable space or less (or a JADU of 500 or less). Above 750 square feet, impact fees must be proportional to those for the primary dwelling.
Connection or capacity charge
A utility’s charge for hooking up and for the capacity you take. Connection and capacity charges are NOT impact fees. Budget it separately, always.
Declared permit valuation
Declared permit valuation is what an applicant writes on a form so a city can compute a fee. It is not a construction cost, it is not a bid, and it is not what the job was sold for. Where a fee scales with the number written down, the number written down has an obvious direction of error.
Fair Market Rent (FMR)
FMR is a 40th-percentile policy construct (gross rent including utilities) used for Housing Choice Vouchers. It is not observed ADU asking rent and not ACS median gross rent.
Small Area FMR
FMR published by ZIP rather than by metropolitan area, used for the voucher program in several metros. Where it applies, the metro figure can be badly wrong for a specific neighborhood.
Pre-approved plan
A plan set an agency has already reviewed and posted. A complete application for a DETACHED ADU that uses a plan preapproved in the current triennial California Building Standards Code cycle, or a plan identical to one the agency already approved in that cycle, must be approved or denied ministerially within 30 days.
Table A2
The Annual Progress Report table California jurisdictions file with HCD, carrying permits and completions in separate columns. It is where the 41% unmatched share on this page comes from.
What these tools will and will not do
The standing promises, stated once here so they need not be repeated on all nine pages.
The arithmetic is on the page
Every calculator states the formula it runs and the source behind any constant. If you disagree with an assumption you can see it and change the input.
Nothing is emailed and nothing is stored
The tools run in your browser. No email wall standing between you and a number you could work out on paper.
No tool will tell you your lot qualifies
Parcel-level feasibility depends on easements, soils, utilities, fire severity zones, coastal overlays and local implementation that no website can see. Every page that touches this produces questions for the counter instead.
No national or state average is shipped as your budget
We hold no dataset of ADU bids, quotes or contracts. Every dollar figure on this site is a named third party’s published figure, arithmetic we performed on one and have labeled as ours, or a number you typed in.
Third-party figures stay labeled as theirs
The construction-cost medians on this site are from a 2021 survey and are cited as its authors’.
Where we indexed them forward, the arithmetic is labeled as ours and the index publisher’s own disclaimer is printed alongside: "The ENR BCI reports cost trends for specific construction trade labor and materials in the California market and does not reflect current market bidding environment."
They will tell you the numbers do not work
That is what allows these tools to conclude that the numbers do not work, that the answer is to keep the garage, or that the honest next step is a question at the planning counter rather than a deposit.
This is not legal, tax, financial or construction advice
HyreADU does not design, permit or build accessory dwelling units. It does not appraise, lend, invest, let property or prepare taxes, it does not rank or refer contractors, and it takes no referral fee from anyone who does any of those things.
Seven states, and the three objections legislatures keep removing
Seven states, seven different drafting styles, and the same three objections removed in most of them: replacement parking, owner-occupancy, and a requirement that the unit match the house.
Several also attach a self-executing penalty — California deems the application approved, Arizona removes the city’s limits entirely, Montana voids the regulations — which tells you legislatures expected local resistance and drafted against it.
State
Citation
What it actually does
The clause worth quoting at someone
California
Gov. Code §§ 66310–66342
Ministerial approval on a 60-day clock with deemed approval, no replacement parking, no owner-occupancy requirement, and no fire sprinklers triggered in the existing house.
—
Washington
RCW 36.70A.681 (HB 1337, 2023)
A hard 50 per cent cap on ADU impact fees relative to the principal unit, and detached units must be permitted.
“may not assess impact fees on the construction of accessory dwelling units that are greater than 50 percent of the impact fees that would be imposed on the principal unit”
Montana
MCA 76-2-345 (SB 528, ch. 502, L. 2023)
One ADU by right, sized at 75 per cent of the house or 1,000 square feet, whichever is less. If a municipality misses the compliance deadline its own regulations are void.
“A municipality shall adopt regulations under this chapter that allow a minimum of one accessory dwelling unit by right on a lot or parcel that contains a single-family dwelling.”
Colorado
C.R.S. § 29-35-103 (HB24-1152)
No new off-street parking, no owner-occupancy requirement, no restrictive design standard — and homeowners association covenants banning ADUs are void as a matter of public policy, including ones adopted before the law, subject to a defined "reasonable restriction" carve-out.
C.R.S. § 38-33.3-106.5(4)(a): “NO PROVISION OF A DECLARATION, BYLAW, OR RULE OF AN ASSOCIATION THAT IS ADOPTED ON OR AFTER THE EFFECTIVE DATE OF THIS SUBSECTION (4) MAY RESTRICT THE CREATION OF AN ACCESSORY DWELLING UNIT … IN ANY WAY THAT IS PROHIBITED BY SECTION 29-35-103, AND ANY PROVISION OF A DECLARATION, BYLAW, OR RULE THAT INCLUDES SUCH A RESTRICTION IS VOID AS A MATTER OF PUBLIC POLICY.”
Arizona
A.R.S. § 9-461.18 (HB 2720, 2024, as engrossed)
Municipalities over 75,000 must permit at least one ADU by right, may not require additional parking, a familial or employment relationship between occupants, matching exterior design, or a restrictive covenant — and a city that missed the deadline loses its limits entirely.
“IF A MUNICIPALITY FAILS TO ADOPT DEVELOPMENT REGULATIONS AS REQUIRED BY THIS SECTION ON OR BEFORE JANUARY 1, 2025, ACCESSORY DWELLING UNITS SHALL BE ALLOWED ON ALL LOTS OR PARCELS ZONED FOR RESIDENTIAL USE IN THE MUNICIPALITY WITHOUT LIMITS.”
Maine
30-A M.R.S. § 4364-B (LD 2003 and later amendments)
A statutory amnesty for units built without municipal approval, a 190-square-foot minimum size, one ADU exempt from density calculations, no additional parking, and no owner-occupancy.
“An accessory dwelling unit that was not built with municipal approval must be allowed if the accessory dwelling unit otherwise meets the requirements for accessory dwelling units of the municipality and under this section.”
Oregon
ORS 197A.425 (formerly ORS 197.312(5)–(6))
At least one ADU for each detached single-family dwelling in cities over 2,500 and counties over 15,000 inside urban growth boundaries. Reasonable local siting and design regulation excludes owner-occupancy requirements and additional off-street parking.
Retrieved from a private reproduction of the Oregon Revised Statutes, not from oregonlegislature.gov, which returned no content. Treated as second-tier sourcing and not quoted verbatim on this site.
Vermont, New Hampshire, Rhode Island and Utah were on our list and are not here. We could not retrieve a statute, bill text or state agency page for any of them on the retrieval date, so this site says nothing about them.
Montana SB 323 of 2023 is the DUPLEX bill, not the ADU bill. The ADU statute came from SB 528. Guides that attribute Montana ADU law to SB 323 have the wrong bill.
Legal to build is not the same as possible to finance
Two rules from the secondary mortgage market that no state legislature amended when it liberalised ADU zoning. They are the mechanism behind the completion gap at the top of this page.
Fannie Mae — the square footage does not roll up
Selling Guide B4-1.3-05, Improvements Section of the Appraisal Report, guide date June 04, 2025: “An ADU is generally an additional living area independent of the primary dwelling that may have been added to, created within, or detached from the primary dwelling.” And: “The ADU must have basic requirements for living, sleeping, cooking, and bathroom facilities on the same parcel as the primary dwelling.”
The guide keeps ADU living area OUT of the primary dwelling’s finished above-grade square footage, requiring it to be reported and adjusted separately in the sales comparison grid unless it sits within the primary dwelling with interior access and above grade. That is our reading of the retrieved section rather than a verbatim quotation.
So the 800 square feet you built does not simply get added to the house’s square footage and multiplied by a neighborhood rate.
Its value has to be carried by a separate adjustment the appraiser must support with market evidence — and in a neighborhood where few comparable sales have an ADU, that evidence may not exist.
Freddie Mac — legal, or legal non-conforming
Freddie Mac’s ADU page states: “ADUs on 1-, 2- and 3-unit properties must be legally permissible by jurisdiction, legal non-conforming or be located in an area without zoning.”
On income: “Borrowers may be able to use ADU income to qualify for home financing on their subject 1-unit primary residence (Guide Chapter 5306) or non-subject investment property (Guide Chapter 5306).”
That eligibility sentence is a hard gate, and it is the reason an unpermitted conversion is a financing problem rather than a paperwork problem. It is also why Maine’s statutory amnesty for units built without municipal approval is more consequential than it first looks: legalizing the unit is what makes it financeable.
Putting the two together: a state can make an ADU legal to build, quickly and without a hearing, and still leave it hard to finance — because the permission is granted by a planning statute and the money is governed by a secondary-market guide that no legislature amended.
That is our analysis of the retrieved material, not a claim either enterprise makes.
Eight things we looked for and could not confirm
Published because a site that never says “we could not confirm this” is not being careful, it is being quiet. None of these appears as a claim anywhere on HyreADU.
The claim
What actually happened
Anything from the California HCD ADU Handbook
Every hcd.ca.gov ADU page and PDF returned 403 to automated retrieval, through two different clients. The handbook is widely described as existing and recently updated; we hold no quotation from it and publish none.
An IRC edition label on the habitability figures
ICC’s own code library returned 403. The R310 and R305 text on this site came from a county-posted Code and Commentary excerpt and a city code handout, neither of which states its edition on its face. The figures are presented as model-code figures without an edition label.
Anything about FHA 203(k) or FHA treatment of ADU rental income
The relevant FHA mortgagee letter on hud.gov returned 403 to two clients. No FHA material is published on this site.
HUD PD&R and Census/American Housing Survey data on ADUs
Every huduser.gov page attempted returned empty content, and no Census or AHS ADU figure was retrieved. Nothing from either appears here.
A dollar figure for any city or utility ADU connection or capacity charge
No municipal or utility fee schedule was retrieved. We publish the statutory caps and prohibitions, and tell you to get your own two utilities’ figures in writing. Shipping an invented magnitude would be worse than shipping none.
A sunset or expiry on California’s owner-occupancy prohibition
We looked and did not find one, and we did not retrieve the separate JADU article, which has its own treatment. The prohibition is stated for ADUs, without a sunset claim in either direction.
ADU statutes in Vermont, New Hampshire, Rhode Island and Utah
On our list, and dropped. No statute, bill text or state agency page was retrieved for any of the four, so this site says nothing about them.
Consumer Financial Protection Bureau guidance specific to ADUs
None found. Only general Regulation Z material with no ADU content. Dropped rather than stretched.
What HyreADU is, and what it is not
We do not build. HyreADU does not design, permit or build accessory dwelling units. It does not appraise, lend, invest, let property or prepare taxes, it does not rank or refer contractors, and it takes no referral fee from anyone who does any of those things.
We hold no dataset of bids. We hold no dataset of ADU bids, quotes or contracts. Every dollar figure on this site is a named third party’s published figure, arithmetic we performed on one and have labeled as ours, or a number you typed in.
Where we do hold data, we say exactly what it is. This site publishes a research desk that works from California’s own published files — HCD’s Annual Progress Report, municipal open-data permit extracts, HUD’s Fair Market Rent documentation.
Every one of those studies carries its method, its exclusions and what it could not compute. Two cities are missing from the permit-timing study because they publish no application date, and saying so is more useful than substituting a proxy.
Why that matters to you. That is what allows these tools to conclude that the numbers do not work, that the answer is to keep the garage, or that the honest next step is a question at the planning counter rather than a deposit.
A calculator built by a design-build firm cannot easily conclude that the utility connection makes the project unviable, or that the honest answer is to wait two years. These can.
Geography, honestly. The statutes and the datasets on this site are overwhelmingly Californian, because California is where the law is most developed and the data most complete.
The arithmetic in the tools is general; the citations are not, and a reader elsewhere should treat the California material as an illustration of what to look for in their own state rather than as their own rules.
Questions this calculator answers
Will I have to replace the parking if I convert my garage?
Not in California. Gov. Code § 66314(d)(11): “When a garage, carport, covered parking structure, or uncovered parking space is demolished in conjunction with the construction of an accessory dwelling unit or converted to an accessory dwelling unit, the local agency shall not require that those offstreet parking spaces be replaced.” And where parking is required at all, Gov. Code § 66314(d)(10)(A) caps it at one space per unit or per bedroom, whichever is less, and allows it as tandem parking on a driveway.
Can my city require me to live on the property?
Not in California. Gov. Code § 66315 states that no standards beyond § 66314 may be imposed, “including an owner-occupant requirement”, except that the agency may require rentals be for terms of 30 days or longer. Colorado, Washington, Oregon and Maine each remove owner-occupancy requirements too. One caveat: we did not retrieve California’s separate junior ADU article, which has its own treatment, so do not read this as covering a JADU.
How long does an ADU permit actually take?
The statute and the observed data say different things, and both are true. Gov. Code § 66317(a)(3) requires a decision within 60 days of a completed application, with the application deemed approved if the agency misses. The observed medians from application-side date to issuance are 162 days in Los Angeles, 174.5 in unincorporated Marin and 445 in San Francisco. Those measure a longer span than the statute — they include every day spent curing an incomplete set — which is why a median above 60 days is not a finding that anyone missed the clock.
Are ADUs exempt from impact fees?
Impact fees may not be imposed on an ADU of 750 square feet of interior livable space or less (or a JADU of 500 or less). Above 750 square feet, impact fees must be proportional to those for the primary dwelling. But read the next sentence carefully, because it is where budgets break: Connection and capacity charges are NOT impact fees. Under § 66311.5(b), an ADU is not a new residential use for connection-fee purposes unless it is built together with a new single-family dwelling — but the utility can still bill a connection or capacity charge, and that bill is outside the impact-fee prohibition entirely.
What does an ADU cost to build?
We hold no dataset of ADU bids and ship no figure as your budget. The published figures that exist are a 2021 California owner survey with a median of $150,000 — in which 37% came in under $100,000 and 71% under $200,000, so the spread is enormous — and our own indexation of that survey forward, which the index publisher itself cautions “The ENR BCI reports cost trends for specific construction trade labor and materials in the California market and does not reflect current market bidding environment.” Declared permit valuation, which circulates as if it were cost, is not: Declared permit valuation is what an applicant writes on a form so a city can compute a fee. It is not a construction cost, it is not a bid, and it is not what the job was sold for. Where a fee scales with the number written down, the number written down has an obvious direction of error.
What rent should I assume in an ROI calculation?
Look up HUD’s Fair Market Rent for your own area rather than taking a number from a calculator. FMR is a 40th-percentile policy construct (gross rent including utilities) used for Housing Choice Vouchers. It is not observed ADU asking rent and not ACS median gross rent. And note that in the 2021 owner survey only 51% of units were generating rental income at all, while 16% housed a relative at no cost — for that second group an ROI calculation is the wrong instrument.
Why do so many permitted ADUs never get finished?
Our reading is that the binding constraint is money rather than zoning, and two secondary-market rules are part of the mechanism. Fannie Mae’s guide keeps ADU living area out of the primary dwelling’s above-grade square footage, so its value has to be carried by a separate appraisal adjustment that market evidence must support. Freddie Mac requires that ADUs “ADUs on 1-, 2- and 3-unit properties must be legally permissible by jurisdiction, legal non-conforming or be located in an area without zoning.” Putting the two together: a state can make an ADU legal to build, quickly and without a hearing, and still leave it hard to finance — because the permission is granted by a planning statute and the money is governed by a secondary-market guide that no legislature amended. That is our analysis of the retrieved material, not a claim either enterprise makes.
Does a pre-approved plan speed things up?
There is a statutory route. Under Cal. Gov. Code § 65852.27 (AB 1332 (Carrillo, 2023), effective 2025-01-01), a complete application for a detached ADU using a plan preapproved in the current code cycle carries a 30-day ministerial decision. By its terms that clock does not reach attached ADUs, garage conversions or JADUs unless a local program separately covers them, and whether your agency has a usable catalog is a separate question — see the research on it.
Can a homeowners association stop me building an ADU?
It depends entirely on the state, and the two we verified take opposite routes. Colorado voids the covenant: under C.R.S. § 38-33.3-106.5(4)(a), an association provision restricting an ADU in a way § 29-35-103 prohibits “is void as a matter of public policy”, including provisions adopted before the law, subject to a defined reasonable-restriction carve-out. Arizona instead bars the municipality from requiring a restrictive covenant, but does not void private ones. We verified no other state on this question.
What ceiling height and window does a bedroom need?
Model-code figures, and the caveats matter. IRC R305.1, ceiling height: “Habitable space, hallways and portions of basements containing these spaces shall have a ceiling height of not less than 7 feet (2134 mm). Bathrooms, toilet rooms and laundry rooms shall have a ceiling height of not less than 6 feet 8 inches (2032 mm).” IRC R310, emergency escape and rescue openings requires a net clear opening of not less than 5.7 square feet, a minimum net clear height of 24 inches, a minimum net clear width of 20 inches, and the bottom of the clear opening not more than 44 inches above the floor. The IRC is a model document with no legal force until a jurisdiction adopts it, and adopting jurisdictions routinely amend it. Confirm every figure with the authority that will inspect the work. Neither retrieved document states its IRC edition on its face. The numbering matches the 2021 structure and identical language appears in a state adoption of the 2018 edition, so we present these as model-code figures without an edition label rather than assert one we did not verify.
Does HyreADU build ADUs or recommend a builder?
No to both. We do not design, permit, build, appraise, lend, let or prepare taxes, we rank and refer nobody, and we take no referral fee. That is precisely why these tools can conclude that the utility connection makes the project unviable, or that the honest answer is to wait.
Sources and methodology
Figures dated 5 September 2026. Last reviewed .
LADBS Building and Safety — Building Permits Issued from 2020 to Present (N) (Los Angeles, retrieved 2026-09-05. HyreADU analysis of issued ADU building permits: n=27,188, median 162.0 calendar days from application to issuance (IQR 79.0-301.0). Measures a different span from the statutory decision clock.)
DataSF Building Permits (DBI Permit Tracking System extract) (San Francisco, retrieved 2026-09-05. HyreADU analysis of issued ADU building permits: n=1,713, median 445 calendar days from application to issuance (IQR 276-707). Measures a different span from the statutory decision clock.)
Marin County Community Development Agency — Building Permit (mkbn-caye) (Marin County (unincorporated), retrieved 2026-09-05. HyreADU analysis of issued ADU building permits: n=472, median 174.5 calendar days from application to issuance (IQR 105.0-308.2). Measures a different span from the statutory decision clock.)
Gov. Code § 66314 — standards for accessory dwelling units (California Legislature, retrieved 2026-09-05. Source of the prohibition on requiring replacement off-street parking, the one-space cap, the concurrent demolition permit rule, the four-foot setback rule and the fire sprinkler provision.)
Gov. Code § 66315 — no additional standards, including owner occupancy (California Legislature, retrieved 2026-09-05. Quoted in full on this page. Added by SB 477, effective 25 March 2024. We did not retrieve the separate junior ADU article and make no claim about JADU owner-occupancy.)
Gov. Code § 66317 — ministerial approval, the 60-day clock and the completeness determination (California Legislature, retrieved 2026-09-05. Source of the ministerial requirement, the 60-day decision with deemed approval, the tolling provision, the 15-business-day completeness determination and the rule that no other local ordinance may be the basis for delay or denial. As amended by SB 543, effective 1 January 2026.)
Gov. Code §§ 66321 and 66323 — size, height and the by-right units (California Legislature, retrieved 2026-09-05. Source of the prohibitions on minimum-size and maximum-size standards, the 800 square feet with four-foot setbacks provision, the height floors, the by-right ministerial approval, the bar on extra objective standards and the rule that nonconforming zoning conditions may not be required to be corrected.)
Gov. Code § 66311.5 — impact fees, connection fees and capacity charges (California Legislature, retrieved 2026-09-05. Source of the 750 square foot impact-fee prohibition, the proportionality rule above it, the rule that an ADU is not a new residential use for connection-fee purposes, and the exclusion of connection fees and capacity charges from the definition of impact fee. Renumbered from § 66324 by SB 543, effective 1 January 2026.)
Cal. Gov. Code § 65852.27 — pre-approved plan programs (California Legislature, retrieved 2026-09-05. AB 1332 (Carrillo, 2023), effective 2025-01-01. Source of the 30-day ministerial decision for a detached ADU using a current-cycle preapproved plan, and of the requirement that every local agency develop a program.)
Housing Element Annual Progress Report, Table A2 (California Department of Housing and Community Development, Housing Element Annual Progress Report, Table A2, retrieved 2026-09-05. Source of the permit and completion columns. 281,321 ADU rows across 511 jurisdictions, 2018-2025. The cohort unmatched share is a HyreADU calculation on that file, with the method and its limitations on our research page.)
Building permit open data — LADBS, DataSF and Marin County (City of Los Angeles; City and County of San Francisco; Marin County, retrieved 2026-09-05. Source of the observed application-to-issuance durations. HyreADU calculation. Sacramento and San José are excluded because neither publishes an application-side date, so no duration can be computed for them.)
Fair Market Rents, FY2026 (HUD Office of Policy Development and Research, retrieved 2026-09-05. FMR is a 40th-percentile policy construct (gross rent including utilities) used for Housing Choice Vouchers. It is not observed ADU asking rent and not ACS median gross rent.)
RCW 36.70A.681 — accessory dwelling units (Washington State Legislature, retrieved 2026-09-05. Quoted only for the 50 per cent impact-fee cap and the requirement to permit detached units. The remaining subsections were retrieved as paraphrase and are not quoted here.)
MCA 76-2-345 — accessory dwelling units (Montana Code Annotated, retrieved 2026-09-05. Source of the by-right requirement and the 75 per cent or 1,000 square foot size rule. Note that Montana SB 323 of 2023 is the duplex bill; the ADU statute came from SB 528.)
HB24-1152 as enacted — C.R.S. §§ 29-35-103 and 38-33.3-106.5 (Colorado General Assembly, retrieved 2026-09-05. Source of the administrative approval requirement, the parking and owner-occupancy prohibitions, and the provision voiding homeowners association restrictions as a matter of public policy.)
HB 2720 (House Engrossed) — A.R.S. § 9-461.18 (Arizona State Legislature, retrieved 2026-09-05. Source of the by-right requirement for municipalities over 75,000, the parking, relationship, design-matching and restrictive-covenant prohibitions, and the self-executing consequence for a city that missed the deadline. Retrieved as engrossed; the chaptered session law was not retrieved.)
30-A M.R.S. § 4364-B — accessory dwelling units (Maine Legislature, retrieved 2026-09-05. Source of the requirement to allow units built without municipal approval, the 190 square foot minimum size, the density exemption, the parking rule and the owner-occupancy provision.)
Selling Guide B4-1.3-05, Improvements Section of the Appraisal Report (Fannie Mae, retrieved 2026-09-05. Guide date June 04, 2025. Source of the ADU definition and the basic-requirements sentence. The treatment of ADU area in the sales comparison grid is our reading of the retrieved section and is labeled as such.)
Accessory Dwelling Units (Freddie Mac, retrieved 2026-09-05. Source of the ADU rental income position and of the requirement that ADUs be legally permissible, legal non-conforming, or in an area without zoning.)
IRC R310 (Routt County, Colorado, retrieved 2026-09-05. Jurisdiction-published copy of the ICC Code and Commentary for R310. ICC’s own code library returned 403 to automated retrieval on 2026-09-05. The text below comes from jurisdiction-published copies, named in the sources. Neither retrieved document states its IRC edition on its face. The numbering matches the 2021 structure and identical language appears in a state adoption of the 2018 edition, so we present these as model-code figures without an edition label rather than assert one we did not verify.)
IRC Code Handout #434 — Ceiling Height, R305 (City of Boise, Idaho, retrieved 2026-09-05. Jurisdiction-published handout carrying the R305 ceiling height text. The IRC is a model document with no legal force until a jurisdiction adopts it, and adopting jurisdictions routinely amend it. Confirm every figure with the authority that will inspect the work.)
Related
ResearchThe studies these tools read from, each with its method and its exclusions.
Editorial policyHow these pages are written, sourced and corrected.