Box Elder County · 12,677 residents
Tremonton ADU rules
Tremonton: internal ADUs allowed; detached ADUs allowed. Owner occupancy applies.
Internal ADU (inside the home)
Detached ADU (backyard building)
✓ Checked against city sources on September 24, 2026 See sources
Tremonton ADU rules at a glance
| Rule | Internal ADU (basement, attic, inside the home) | Detached ADU (backyard building) |
|---|---|---|
| Allowed? | Allowed | Allowed |
| Minimum lot | Not yet verified — confirm with the city | Tremonton does not set a separate lot minimum for detached ADUs; they are allowed in single-family zones whose smallest lot size is 8,000 sq ft (R1-8), as long as parking, setback and site-design rules can be met. |
| Owner occupancy | The property owner (as shown on Box Elder County tax rolls) must live in the main home or the ADU as a full-time resident, meaning at least 8 months of every 12; the permit can continue during a temporary absence if the owner notifies the city, and lapses after 24 months unless extended. | The property owner (as shown on Box Elder County tax rolls) must live in the main home or the ADU as a full-time resident, meaning at least 8 months of every 12; the permit can continue during a temporary absence if the owner notifies the city, and lapses after 24 months unless extended. |
| Parking | At least one off-street parking space for the ADU in addition to the home's parking, plus one more if the ADU has two or more bedrooms; parking for the home and ADU must be independently accessible and hard-surfaced. | At least one off-street parking space for the ADU in addition to the home's parking, plus one more if the ADU has two or more bedrooms; parking for the home and ADU must be independently accessible and hard-surfaced. |
| Size limits | Not yet verified — confirm with the city | At least 300 sq ft, smaller than the main home, and covering no more than 30% of the rear yard (40% if combined with another accessory use in the same building). |
| Setbacks | Must meet the zone's minimum setbacks for the main home. | Must meet the zone's minimum setbacks for an accessory building; no building on a public utility easement. |
| Zones | Allowed as a permitted use in the RR-1, R1-20, R1-12, R1-10 and R1-8 residential zones; not allowed in multifamily housing or on nonconforming single-family lots. | Allowed as a permitted use in the RR-1, R1-20, R1-12, R1-10 and R1-8 residential zones; not allowed in multifamily housing or on nonconforming single-family lots. |
| Permit process | Accessory Dwelling Unit Permit approved administratively by the Zoning Administrator, with site plan, floor plan (and elevations for detached units) and the city fee; may be filed together with the building permit. ADUs do not pay impact fees. | Accessory Dwelling Unit Permit approved administratively by the Zoning Administrator, with site plan, floor plan (and elevations for detached units) and the city fee; may be filed together with the building permit. ADUs do not pay impact fees. |
What the Tremonton council decided
Recorded votes and actions on ADU rules, linked to the public meeting record on OpenUtah.
· City Council
Adopted Ord. 26-10 amending Chapters 1.03 and 1.07: defined small accessory structures, fixed accessory/main building height discrepancy, changed side setbacks for ADUs, allowed single-family homes in RM-8/RM-16 (5-0 roll call)
Read the meeting record
Proposed or pending changes
Not adopted as of September 24, 2026. They do not change the rules above until the city adopts them.
- Ord. 26-10 (adopted July 7, 2026) changed ADU side setbacks and building-height wording in Chapter 1.07, but the online code is codified only through Ord. 26-02; the new numbers were not available, so height is left null and setbacks are described only by reference to the zone's accessory-building rules.
- Ord. 26-10 also allows single-family homes in RM-8 and RM-16; whether ADUs become allowed with those homes is not confirmed.
State law: detached ADUs from October 1, 2026
Tremonton 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 Tremonton 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; Tremonton makes the decision.
- No numeric external minimum is recorded for Tremonton. The map keeps the statewide 11,000 sq ft external screen and shows the researched status (generally allowed) on the property report.
- "Likely" above 15,000 sq ft is this site's planning band for a large recorded lot. It is not a sentence in the Tremonton 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.
Sources
We link only to government sources and public meeting records. Codes change; confirm the current version with Tremonton before you apply.
- Tremonton City Council meeting packet, July 21, 2026 (draft minutes of July 7, 2026)
Council adopted Ord. 26-10 amending Chapters 1.03 and 1.07, including side setbacks for ADUs and accessory-building height rules (5-0).
- Utah S.B. 284 (2026) enrolled — Utah Code 10-21-304
Statewide detached-ADU rules effective Oct. 1, 2026.
- U.S. Census Bureau Vintage 2024 Utah city population estimates
2024 population 12,677; Box Elder County 64,120.
- Utah Code 10-2-301 — classification of municipalities
10,000-29,999 = fourth class.
- Utah Code 17-50-501 — classification of counties (superseded 2021 text)
31,000-124,999 = third-class county; confirm against the current recodified section.
- Official Tremonton website
Common Tremonton ADU questions
Can you build an ADU in Tremonton?
Tremonton: internal ADUs allowed; detached ADUs allowed. Owner occupancy applies. This is planning guidance, not a permit. Confirm the zone on your parcel with Tremonton.
What lot size does Tremonton require for an ADU?
Internal ADU: Not yet verified — confirm with the city. Detached ADU: Tremonton does not set a separate lot minimum for detached ADUs; they are allowed in single-family zones whose smallest lot size is 8,000 sq ft (R1-8), as long as parking, setback and site-design rules can be met.
Does Tremonton require the owner to live on the property?
Internal ADU: The property owner (as shown on Box Elder County tax rolls) must live in the main home or the ADU as a full-time resident, meaning at least 8 months of every 12; the permit can continue during a temporary absence if the owner notifies the city, and lapses after 24 months unless extended. Detached ADU: The property owner (as shown on Box Elder County tax rolls) must live in the main home or the ADU as a full-time resident, meaning at least 8 months of every 12; the permit can continue during a temporary absence if the owner notifies the city, and lapses after 24 months unless extended.
How much parking does a Tremonton ADU need?
Internal ADU: At least one off-street parking space for the ADU in addition to the home's parking, plus one more if the ADU has two or more bedrooms; parking for the home and ADU must be independently accessible and hard-surfaced. Detached ADU: At least one off-street parking space for the ADU in addition to the home's parking, plus one more if the ADU has two or more bedrooms; parking for the home and ADU must be independently accessible and hard-surfaced.
What does it cost to build an ADU in Tremonton?
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 Tremonton?
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 Tremonton 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
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Utah ADU Builder provides educational planning guidance. This page is not legal advice and not a permit. Population: U.S. Census Bureau population estimate (2024). Editorial standards.