Published: 5 Oct 2026 · Last verified: 5 Oct 2026 · Next review: Jan 2027 Cost figures are re-checked against permit records quarterly. Changes are logged in Corrections.
This is the first post in our national series, and it is not a build estimate. Every other post on this site prices one plan in one place across the same six phases. This one does something different: it takes the five wildest government-fee findings from our 148-city national dataset — the top three most populous cities in every state, researched line by line from official sources — and puts them side by side.
The through line is the one this site keeps finding: the building permit is rarely the story. The story is the stack.
1. Montgomery County, Maryland — the $59,854 square foot
Maryland state law (Land Use §4–506(A)) prohibits any development impact fee on an ADU under 750 square feet. At exactly 750, the exemption ends — and Montgomery County’s published impact taxes kick in at up to $31,301 per unit for schools plus $28,553 for transportation: $59,854 combined (county impact tax handout, effective July 1, 2025).
Two honest caveats, because the number needs them. First, that is an upper bound: the county publishes the per-dwelling-unit single-family-detached rate and no ADU-specific category, and §4–506(B) requires any fee at 750 sq ft to be assessed proportionately rather than as a de facto prohibition — a proration the county has not publicly quantified for ADUs. Second, even the building permit is dwarfed: the school impact tax alone is 52 to 54 times the county’s $575.90 residential building permit fee for the same structure. The permit is the cheapest line item by two orders of magnitude.
2. Portland, Oregon — the $12,028 park fee that can be $0
Portland’s parks system development charge on a 750 sq ft ADU is $12,028 (the “700–1,199 sq ft” residential bracket, non–Central City) — about seven times the city’s transportation SDC of $1,762 for the same unit (Parks SDC schedule, FY26–27).
And then the waiver: Portland’s ADU SDC Waiver Program wipes all SDCs — transportation, parks, water, environmental services — to $0 if the owner records a covenant barring short-term rental of the ADU and the house for 10 years. Break the covenant and the city can claw back 150% of the current rates. One recorded document moves roughly $14,000 off the invoice. Few American cities offer a swing that large for a signature.
For completeness: Portland does charge a school construction excise tax of $1.70 per square foot ($1,275 on 750 sq ft), and water Bureau SDC is $0 if the ADU shares the existing meter — $5,483 only if you upsize to a new 5/8” meter.
3. Memphis, Tennessee — where our 750 sq ft benchmark is illegal
Every post in our California series prices a 750 sq ft ADU. In Memphis, that unit cannot be permitted on a standard lot. The Unified Development Code (Sec. 2.7.3) caps ADUs at 700 sq ft — 1,000 only in rural RE/CA districts — and bars them outright on lots under 10,000 sq ft.
The fee stack that remains is instructive for the opposite reason. The building permit for a 750 sq ft dwelling is $125 (the $0.07/sq ft math never escapes the minimum) plus a $50 application fee — among the cheapest in our dataset, 10 to 40 times less than comparable California cities. But the sewer development fee is $3,383 for a 3/4” meter — 27 times the permit — assessed only when the project needs an additional or enlarged water meter (Ordinance 5793, Sec. 33-62). Share the existing meter and it is $0. In Memphis the meter decision, not the permit counter, is the fee event. Tennessee, notably, has no statewide school developer fee at all.
4. Cheyenne vs. Gillette, Wyoming — the same state, 196 times apart
Wyoming gives us the cleanest same-state comparison in the dataset. In Cheyenne, the Board of Public Utilities charges a water System Development Fee of $11,750 for a 3/4” meter (BOPU FY 2026 budget, adopted April 2025, effective October 1, 2025) — a single utility capacity charge larger than the city’s entire building-permit, plan-review, and impact-fee subtotal combined. Roughly 80% of Cheyenne’s total government cost on our benchmark is water and sewer charges.
Ninety minutes north in Gillette, the building permit for the same 750 sq ft structure is a flat $60 (the 500–1,000 sq ft band), and residential plan review is $0 — “no charge for plan reviews” for one- and two-family (Gillette Code Ch. 5, §5-IV-1). Gillette’s permit is about 19 times cheaper than Cheyenne’s valuation-based equivalent of $1,162. Same state, same structure, same year.
5. The school-fee crown: Elk Grove, California — $7.32 per square foot
California’s developer-fee system produces the highest school fees in the dataset. Elk Grove Unified (Sacramento County) levies $7.32 per square foot under Level 2 — $5,490 on a 750 sq ft ADU — adopted June 24, 2025 (Resolution No. 97 with the April 2025 School Facilities Needs Analysis). That is 1.36 times the 2026 Level 1 statutory cap of $5.38.
The highest figure on paper anywhere is Dublin Unified’s $7.36 — but its 2023 adoption capped effectiveness at one year and we could not find a public re-adoption, so we are not calling it current. Elk Grove’s $7.32 is the confirmed current high. For scale, that single fee exceeds the entire building-permit bill in most of the 148 cities we researched.
The pattern
Put the five side by side and the pattern is the one California taught us, writ national: nobody’s ADU budget is broken by the building permit. It is broken — or saved — by the stack around it: a state-law threshold at 749 vs. 750, a covenant that erases $14,000, a zoning cap that makes the benchmark illegal, a water meter charge bigger than everything else combined, a school district line that costs more than some cities’ entire fee schedule.
That is why this site prices the whole stack, line by line, in every city. The 148-city dataset behind this post is the bench we will keep drawing from — one place at a time, same as always.
What we could not confirm
- Montgomery County ADU proration: how the county applies the per-unit SFD impact-tax rate to a 750 sq ft ADU under §4–506(B)‘s proportionality rule. Not published; the $59,854 is the upper bound.
- Dublin Unified $7.36: whether the district re-adopted Level 2 fees after the 2023 resolution’s one-year effectiveness window. Not found in public documents.
- Portland waiver processing time: the covenant must be recorded before permit issuance; we did not verify current processing timelines with PP&D.