The decision table
| ADU | Addition | |
|---|---|---|
| Cost, as filed | The larger of the two in San Diego, Honolulu, Anaheim, Bellingham and Denver; the smaller in San Francisco and Palo Alto | See the city table; the usual addition ranges from $50,000 in Anaheim to $230,000 in San Francisco |
| Time, permit to final | Long: 442 days in San Diego, 533 in Honolulu, 567 in San Francisco | Also long: 343 days in San Diego, 567 in Honolulu, 621 in San Francisco |
| Permits and approval | In California, local agencies must approve qualifying ADUs ministerially, may not set a maximum size below 850 sq ft (1,000 sq ft for more than one bedroom), and may not charge impact fees on ADUs under 750 sq ft (HCD fact sheet, April 2026) | Standard building permit; discretionary review where the city requires it; no state ADU protections |
| Choose it when | You want rentable or separately occupied space, or a unit for family | You want more room in the house you live in, connected to it |
| Resale | Not in the file; we have no sourced figure | Not in the file; we have no sourced figure |
What the file shows, city by city
Both trades had at least 100 permits in each city shown. "Usual filed value" is the middle declared value; "finished" is the share of mature permits that reached final; "days" is the usual time from issue to final with open permits counted as unfinished. A dash means the city's file does not record that field for that trade.
| City | Side | Permits | Firms | Usual filed value | Finished | Usual days to final |
|---|---|---|---|---|---|---|
| San Francisco | ADU | 333 | 271 | $169,365 | 52.5% | 567 |
| San Francisco | Addition | 674 | 509 | $230,000 | 52.2% | 621 |
| San Diego | ADU | 1,278 | 640 | $127,372 | 75.1% | 442 |
| San Diego | Addition | 671 | 422 | $85,351 | 82.7% | 343 |
| Honolulu | ADU | 297 | 139 | $150,000 | 79.6% | 533 |
| Honolulu | Addition | 979 | 314 | $100,000 | 59.3% | 567 |
| Anaheim | ADU | 330 | 202 | $100,000 | 94.0% | 307 |
| Anaheim | Addition | 141 | 119 | $50,000 | — | 303 |
| Bellingham | ADU | 110 | 71 | $140,755 | 79.2% | 329 |
| Bellingham | Addition | 131 | 81 | $66,413 | 65.1% | 328 |
| Palo Alto | ADU | 206 | 158 | $108,045 | — | — |
| Palo Alto | Addition | 100 | 90 | $165,313 | — | 554 |
| Denver | ADU | 262 | 162 | $137,144 | — | — |
| Denver | Addition | 864 | 393 | $110,000 | — | — |
Austin has both trades (465 ADU and 3,209 addition permits) but no usable filed value on either, so it is not in the table. Nashville and Raleigh record ADUs but do not split additions out, so there is nothing to compare them with.
Cost: what "filed value" is and is not
The number on a building permit is the declared construction value. Cities use it to compute permit fees, which gives everyone an incentive to declare on the low side, and some cities accept a round figure. That is why Honolulu's usual ADU reads $150,000 and Anaheim's $100,000: round numbers that someone wrote on a form. Treat the column as a floor and a comparison, not a budget. It does not include design fees or utility connections.
What the column is good for: putting a quote in context. If a San Diego builder quotes an ADU at four times $127,372, you can ask what is in the extra. And if a firm's own usual filed value (on its firm page) is a tenth of its competitors', you can ask about that too.
Time: why both take so long
The usual Honolulu addition permit was open 567 days; the usual San Francisco addition, 621. In both cities the ADU closed a little sooner (533 and 567 days). San Diego runs the other way: 442 days for the usual ADU against 343 for the usual addition. Bellingham's two sides are nearly identical at 329 and 328, and so are Anaheim's at 307 and 303.
The time runs from permit issue to final inspection, so it includes the build, every inspection, and whatever waiting happened in between. It does not include the time to get the permit issued, which the file does not record in most of these cities.
The finished shares follow from the time: a trade where the usual job takes a year and a half will have many permits from the last two years still open. San Francisco's 52.5% for ADUs and 52.2% for additions reflect that as much as anything about the builders. Compare firms within a city and trade, not trades with each other.
Permits and zoning
In California, which covers four of the seven cities here, state law sets the floor for ADUs. HCD's April 2026 fact sheet says jurisdictions must approve ADU applications in residential and mixed-use zones ministerially, may not establish a maximum size of less than 850 square feet (1,000 square feet for an ADU with more than one bedroom), and may not impose impact fees on ADUs of less than 750 square feet; it also cites HCD's March 2025 letter telling the City of Irvine that it cannot impose a deed restriction prohibiting separate sale of an ADU. An addition has none of these protections; it is reviewed under the city's ordinary rules.
For Honolulu, Bellingham and Denver we have not verified the local ADU rules and do not describe them. Ask the planning counter.
What this does not tell you
The file does not know whether the ADU is attached, detached or a garage conversion, or whether the addition is a second storey or a bump-out. It does not know your lot, your setbacks or your neighbours. It does not record what you paid, and it says nothing about what the house will sell for afterwards. We looked for a resale figure we could cite and did not find one we trusted, so there is none here.
How to use this
- Pick your city's ADU and addition lists on the compare pages.
- Set the sliders: for these trades, weight finished share and days to final heavily, because the usual job is long and the open-permit risk is real.
- Look at each shortlisted firm's usual filed value against the city's, and ask about the gap.
- Check the license on the state board (in California, the CSLB license lookup at cslb.ca.gov).
How we know this
Source: each city's open building-permit dataset (San Francisco DBI, City of San Diego, City and County of Honolulu, City of Anaheim, City of Bellingham, City of Palo Alto, City and County of Denver), permits on single-family and duplex lots classified by us into "ADU" and "Addition" from the city's permit descriptions. Windows: 2023-10 to 2026-09 for most cities; Honolulu 2022-07 to 2025-06. Snapshots 1 to 19 October 2026 (Honolulu 1 July 2025). Fields: permit count, distinct firms, declared value (usual = middle value), issue-to-final days with open permits counted as unfinished, finished share of mature permits. A dash means the field is not recorded for that trade in that city. Austin is excluded for lack of a filed value. California ADU rules are quoted from the HCD housing-law fact sheet dated April 2026. No resale figure is given because none with a source we trust was found.
Numbers come from San Francisco DBI building permits on one- and two-family homes, with the contractor from the city's permit contacts file; City of San Diego Development Services approvals; City & County of Honolulu building permits (DPP); City of Anaheim Accela building permits on single-family homes and ADUs; City and County of Denver residential construction and demolition permits; City of Palo Alto Development Center building permits on single-family, duplex and ADU homes; City of Bellingham permits on single-family homes, duplexes and townhomes, data through October 19, 2026. Nobody paid to be on this page and nobody can.
San Francisco ADU builders by permit record →
San Francisco addition contractors by permit record →
San Diego ADU builders by permit record →
San Diego addition contractors by permit record →
Honolulu ADU builders by permit record →
Honolulu addition contractors by permit record →
Anaheim ADU builders by permit record →
Anaheim addition contractors by permit record →
Questions
- Is the filed value what an ADU costs?
No. It is the construction value the contractor or owner declared on the permit. Cities use it to set fees, so it is often conservative. Use it to compare one city or one firm with another, not as a budget.
- Why is the finished share so low for ADUs in San Francisco?
The file records 52.5% of San Francisco ADU permits as finished and 52.2% of additions. Both are long jobs: the usual ADU permit was open 567 days and the usual addition 621. Many permits issued in the last two years simply are not done yet, and our method counts them as unfinished rather than ignoring them.
- Does an ADU need a different permit from an addition?
In the cities here, both are building permits, and each city's file labels them differently enough for us to split them. In California, state law requires local agencies to approve ADU applications in residential and mixed-use zones ministerially, that is, without discretionary review, where the application meets objective standards (HCD fact sheet, April 2026). Additions get no such rule.
- Which adds more to resale value?
We do not know and the permit file cannot say. We found no official or independent source with a figure we would stand behind, so this page makes no resale claim.
- Why is Austin not in the table?
Austin has both trades in its file, with 465 ADU and 3,209 addition permits, but its permit data does not carry a usable filed value for either, so the cost column would be empty. We left it out rather than fill it with a guess.
Build your own list
Every firm with that kind of permit on record. Pick what you value. The list moves.
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