Updated July 10, 2026
The Post Falls ADU build tracker
This tracker is only useful if it's complete. If there's a question I haven't asked or an answer I missed, tell me and I'll add it.
This page tracks my ADU build in Post Falls, question by question. Green means answered, with a source. Gold means partly answered. Grey means I don't know yet.
The ledger at the bottom does the same thing for money: what I can price today, and what I know is coming but can't price yet. I update this page as answers land.
Am I even allowed to build one?
AnsweredDoes Idaho's new ADU law apply to this property?
Yes. Post Falls has more than 10,000 residents, so Idaho Code § 67-6541 (SB 1354) applies. It took effect July 1, 2026.
Source: Idaho Code § 67-6541, checked July 4, 2026.
AnsweredDoes Post Falls allow an ADU on my lot without a public hearing?
Yes. The city permits one ADU per single-family lot (attached, detached, or basement) through an ADU permit plus a building permit. No hearing, no conditional use process.
Source: City of Post Falls ADU page and its ADU information handout, checked July 3, 2026.
OpenCan I rely on the state law's protections before Post Falls updates its own code?
Unknown. And it matters. The city has until February 1, 2027 to bring its code in line with the state law. Whether a homeowner can act on the state limits before that happens is a legal question I need a real attorney to answer, not more reading.
What can I actually build?
PartialHow big can it be?
The rules conflict. The city code caps an ADU at the smaller of 50% of the main house or 1,000 square feet. The state law bars caps below 1,000 square feet or 75% of the main house. Which one governs today is the open legal question above. I wrote up the full conflict here.
Source: PFMC 18.20.190 vs. § 67-6541(2)(d), checked July 4, 2026.
PartialDo I have to live in one of the two units?
The rules conflict. The city code says yes, one of the residences must be owner-occupied. The state law bars cities from requiring that. Same conflict, same unresolved question about which rule governs today.
Source: PFMC 18.20.190 vs. § 67-6541, checked July 4, 2026.
PartialDo I have to add a parking space?
The rules conflict. The city code requires one additional off-street space. The state law bars that requirement, with limited exceptions. Third conflict, same question.
Source: PFMC 18.20.190 vs. § 67-6541, checked July 4, 2026.
OpenWhat setbacks, height limit, and lot coverage apply to my zone?
Unknown. The numbers live in the city's bulk and placement table (PFMC 18.20.040), which I haven't been able to pull yet. I asked the city planning department for them on July 5, 2026 and I'm waiting on the answer.
AnsweredHow many ADUs can one lot have?
One. Every Idaho jurisdiction I've researched so far says the same thing.
Source: Post Falls ADU handout, checked July 3, 2026.
AnsweredDo I need to pay for plans?
Probably not. Four free, pre-approved plan sets are published by the Housing Solutions Partnership and reviewed by building departments across Kootenai County. I broke down all four here. I'm looking hard at using one of them.
Source: Housing Solutions Partnership plan page, checked July 8, 2026.
What does it cost, and how long does it take?
AnsweredDoes the ADU need its own water/sewer hookup, with its own capitalization fee?
No. The city says the ADU must connect to the main house's existing water and sewer service, so no additional capitalization fee applies. That takes the fee schedule's roughly $10,900 new-service charge off the table entirely.
Source: City of Post Falls permit desk, email, July 7, 2026. No public link; compare the published fee schedule for the new-service numbers this replaces.
AnsweredWhat city fees does the project actually owe?
$1,000 to $2,000. The same permits as a house remodel: building permit with plan review, plumbing permits for the ADU and the underground line (about $51), an electrical permit, and a mechanical permit. That range is the city's own estimate, "on the high side." Inspections are included; the city can charge a $100 reinspection fee per incident if you repeatedly schedule inspections before the work is ready.
Source: City of Post Falls permit desk, email, July 8, 2026. No public link; the underlying rates are on the published fee schedule.
OpenDoes the electrical service have capacity for a second dwelling, and what will Avista charge?
Waiting on Avista. I submitted their construction request form on July 5, 2026 and they acknowledged it on July 7. No published fee exists for this anywhere; it's site-specific.
OpenDoes the existing water line or meter need upsizing for the combined load?
Not asked yet. The no-capitalization-fee answer covers fees, not whether the physical line and meter can carry both units.
OpenIs the ADU billed on its own utility account, or through the main house?
Not asked yet.
OpenHow long does city plan review take?
Unknown. Not researched for Post Falls yet. Using a pre-approved plan set should shorten it; by how much is one of the things this build will find out.
OpenWhat's the realistic start-to-occupancy timeline?
Unknown. Nobody publishes this end to end. Documenting the real one is half the point of this page.
How do I pay for it, and what happens after?
OpenHow do people finance an ADU in Idaho?
Unresearched. Cash, HELOC, construction loan, renovation loan, and whether Idaho has any ADU-specific program are all still on the list.
OpenWhat happens to my property taxes after the ADU is assessed?
Unresearched.
OpenWhat happens to my homeowner's insurance?
Unresearched.
The cost ledger
Two kinds of line items: costs I can put real numbers on today, and costs I know are coming but can't price yet. The totals only add up the priced rows, so they will grow as the grey rows turn white.
| Line item | Low | High |
|---|---|---|
| Design and plansAssumes one of the four free pre-approved HSP plan sets. Custom design would put a real number here. | $0 | $0 |
| Water/sewer capitalization feeADU shares the main house's existing connection; no new-service fee. City permit desk, email, July 7, 2026. | $0 | $0 |
| City permits: building + plan review, plumbing, electrical, mechanicalCity's own estimate, "on the high side." Includes the ~$51 underground line permit and all inspections. City permit desk, email, July 8, 2026. | $1,000 | $2,000 |
| Construction: foundation, shell, finishes, site workThe big number. Builder quotes are the next step once plan choice is final. | ? | ? |
| Electrical service capacity check / upgrade (Avista)Request submitted July 5, 2026; acknowledged July 7. No published rate exists. | ? | ? |
| Water/sewer physical tie-in (trenching and plumbing labor)No capitalization fee, but connecting pipe to the house service is real contractor work. Not yet quoted. | ? | ? |
| Property tax increase after reassessment (recurring)Unresearched. | ? | ? |
| Homeowner's insurance change (recurring)Unresearched. | ? | ? |
| Financing costsDepends on how the build is paid for. Unresearched. | ? | ? |
| Total of priced items6 known line items still unpriced. The real total is higher. | $1,000 | $2,000 |
The time ledger
Same idea as the money ledger, but for the calendar. Every step the build needs is on the board in order, and steps that can run at the same time sit on the same columns. Nobody publishes how long any of this takes in Post Falls. I'll fill in each duration as I live through it.
0 done, 2 in progress, 10 not started. 0 of 12 steps have a known duration so far. Left to right is sequence, not scale: bars on the same columns can run at the same time, and a question mark means I don't know how long that step takes yet.