Weber County · 7,833 residents
Plain City ADU rules
Plain City: internal ADUs allowed; detached ADUs allowed with conditions (lot 11,000+ sq ft).
Internal ADU (inside the home)
Detached ADU (backyard building)
Not yet fully verified · last reviewed September 7, 2026 See sources
Plain City ADU rules at a glance
| Rule | Internal ADU (basement, attic, inside the home) | Detached ADU (backyard building) |
|---|---|---|
| Allowed? | Allowed | Allowed with conditions |
| Minimum lot | Statewide statute includes a small-lot pathway around 6,000 sq ft for many internal ADUs — confirm how Plain City applies it on your zone. | 11,000 sq ft. Statewide detached floor for specified municipalities: roughly 11,000 sq ft on qualifying single-family lots (operative Oct 1, 2026). Local code may allow detached ADUs on smaller lots sooner. |
State law: detached ADUs from October 1, 2026
Plain City is a “specified municipality” under Utah S.B. 284. Beginning October 1, 2026, it must permit one detached ADU as a permitted use on a lot of 11,000 sq ft or more that has a detached single-family home. The city can still apply setbacks, height, design, owner-occupancy and limited parking rules, and it may allow detached ADUs on smaller lots. How the state ADU laws work.
How our property map screens Plain City lots
The map colors parcels using the rules on this page and the recorded lot size. A color is a planning screen, not a permit; Plain City makes the decision.
- "Likely" above 15,000 sq ft is this site's planning band for a large recorded lot. It is not a sentence in the Plain City code. Owner occupancy, parking, setbacks, zones, and HOA rules below still have to be checked.
Planned communities, PRDs and PUDs
Reviewed on September 22, 2026 against this city's research file, its published ADU page where one was found, and Utah meeting packets. No adopted sentence was confirmed that allows or bans an ADU in every PUD, PRD, PRUD, or planned community. If the assessor class or subdivision name says PUD, PRD, PRUD, planned unit development, planned residential development, planned community, resort community, or master planned community, the map keeps that lot highly unlikely regardless of size. A plat, CC&Rs, or development agreement can still prohibit an ADU where the zone allows one.
Planning notes for Plain City
Plain City publishes separate applications for internal and detached ADUs, so start by comparing those pathways. The detached-unit code also addresses rental licensing. A measured site plan and your intended occupancy arrangement will help us identify the right application and the standards to resolve before detailed design.
Bring these to your review
- Lot dimensions and building locations
- Internal or detached concept with floor area
- Parking and intended rental use
The question to resolve first
Which application fits this project, and what zoning or rental-license steps accompany it?
Sources
We link only to government sources and public meeting records. Codes change; confirm the current version with Plain City before you apply.
- Plain City forms and applications
City provides separate internal and detached ADU applications
- Utah S.B. 284 (2026), enrolled bill
Statewide detached-ADU requirements for specified municipalities, operative October 1, 2026.
- Official Plain City website
Common Plain City ADU questions
Can you build an ADU in Plain City?
Plain City: internal ADUs allowed; detached ADUs allowed with conditions (lot 11,000+ sq ft). This is planning guidance, not a permit. Confirm the zone on your parcel with Plain City.
What lot size does Plain City require for an ADU?
Internal ADU: Statewide statute includes a small-lot pathway around 6,000 sq ft for many internal ADUs — confirm how Plain City applies it on your zone. Detached ADU: 11,000 sq ft minimum. Statewide detached floor for specified municipalities: roughly 11,000 sq ft on qualifying single-family lots (operative Oct 1, 2026). Local code may allow detached ADUs on smaller lots sooner.
What does it cost to build an ADU in Plain City?
Wasatch Front planning bands are often about $55,000–$145,000 for an internal suite, $70,000–$175,000 for a garage conversion, and $95,000–$250,000 or more for a new detached unit, before unusual site work. These are planning ranges, not bids.
Can an HOA block an ADU in Plain City?
City approval does not override CC&Rs or plat notes. Read the HOA documents and your subdivision plat before you design. A private restriction can stop a unit the city would otherwise allow.
Before you design: general checks for any Utah ADU
General planning advice, not Plain City code.
- Confirm the zoning district on the city zoning map. The county assessor’s “residential” class is not zoning.
- Read your HOA CC&Rs and subdivision plat notes; private restrictions can block a unit the city allows.
- Sketch existing and proposed parking. Driveway geometry and access often decide what fits.
- Ask early about sewer, water and electrical capacity; utilities can force a redesign.
- Expanding a building’s footprint usually triggers full setback and height rules.
Nearby city ADU rules
Want to know what fits on your Plain City lot?
Free, no obligation. We review your parcel against these rules and, if you want, introduce independent design and construction partners. Partners may pay us for referrals.
Utah ADU Builder provides educational planning guidance. This page is not legal advice and not a permit. Population: UGRC POPLASTESTIMATE / Census-derived municipal estimates (manual fill where UGRC blank). Editorial standards.