By the Utah ADU Builders editorial team · Last verified: July 2026 — checked against enrolled S.B. 284 (2026 General Session), Utah Code §10-21-304, and official city and county sources.
Detached ADU Lot Size Requirements in Utah
The number to know is 11,000 square feet. Starting October 1, 2026, Utah Code §10-21-304 requires covered Utah cities to allow a detached ADU — a separate, self-contained home on your lot — on parcels of at least 11,000 sq ft that already hold a single-family house, in zones where single-family homes are permitted. Several cities already allow smaller lots. This guide is for homeowners sizing up a backyard unit before paying for plans. Planning a basement apartment instead? That follows a different rule — no 11,000 sq ft test.
| Question | Short answer |
|---|---|
| Is 11,000 sq ft the Utah detached ADU number? | Yes — for covered cities, beginning October 1, 2026. It's a floor on what cities must allow, not a statewide minimum. |
| Does 11,000 sq ft guarantee approval? | No. Setbacks, lot coverage, utilities, parking, easements, permits, and building codes still apply. |
| Can smaller lots qualify? | Yes. Some Utah cities already allow detached ADUs on 7,000–10,000 sq ft lots. See the city table below. |
| Is this the same as a basement apartment? | No. Detached ADUs and internal (basement) ADUs follow different rules under Utah law. |
| Best next step | Check your property's feasibility before paying for plans or requesting builder estimates. |
See whether your lot size, city, setbacks, parking, and ADU type are likely to work — before you request builder estimates.
Check Detached ADU Feasibility →How big does my lot need to be for a detached ADU in Utah?
Utah's detached ADU lot size requirements work in two layers — a state floor and city rules — and your answer is whichever is more favorable for your parcel. Utah's new law makes covered cities allow detached ADUs on lots of 11,000 sq ft or more starting October 1, 2026, while individual cities set their own minimums — several of them lower. Lot size is the starting line, not the finish line.
Layer 1 — the state floor
Beginning October 1, 2026, a covered Utah city cannot flatly prohibit a detached ADU on a qualifying lot of at least 11,000 sq ft. That's roughly a quarter acre — but not quite. A standard quarter-acre lot is 10,890 sq ft, which misses the state threshold by 110 square feet. If your deed says 0.25 acres, don't assume you clear the bar; check the actual square footage on your county parcel record.
Layer 2 — your city's own rule
The 11,000 sq ft figure is a floor on city obligation, not a ceiling on city permission. State law expressly allows cities to permit detached ADUs on smaller lots, and some already do: unincorporated Salt Lake County allows them at 7,000 sq ft, and Millcreek at 8,000 sq ft. A page that tells you "you need 11,000 square feet in Utah" is simply wrong for those jurisdictions.
Source: Utah Code §10-21-304, enacted by S.B. 284, 2026 General Session .
What does Utah's new 11,000-square-foot rule (S.B. 284) actually mean?
Beginning October 1, 2026, Utah Code §10-21-304 requires a covered municipality to allow a detached ADU as a permitted use — allowed by right under the city's standards rather than by discretionary approval — on a lot of at least 11,000 sq ft that contains a single-family home, in a zone where single-family homes are allowed. The law changes whether a city can tell you no outright. It does not change how you get approved: permits, building codes, and city standards still apply.
Who's covered
The statute applies to a "specified municipality": a city of the first, second, third, or fourth class, or a fifth-class city with a population of 5,000 or more located in a county of the first, second, or third class. In practice, that captures nearly every city along the Wasatch Front and most larger cities statewide. Smaller towns and unincorporated county areas aren't bound by this section — their own ordinances control.
What the rule requires
For a lot to qualify under the state floor, three things must be true: the lot or parcel is at least 11,000 sq ft, it already contains a single-family dwelling, and it sits in a zone where single-family dwellings are a permitted use. Provo — one of the first cities to publish an implementation map — confirms the same criteria and notes that every ADU still goes through city permitting and, where applicable, rental licensing.
What the rule does not do
- ✗It covers detached ADUs only — separate structures like backyard cottages and garage apartments. Internal ADUs (basement apartments and other units inside your home's footprint) are governed by a different section, Utah Code §10-21-303, with its own rules.
- ✗It does not waive permits or codes. State law requires detached ADUs to comply with building, health, and fire codes, and every jurisdiction we reviewed requires a building permit — do not plan around a permit-free path.
- ✗It does not apply to vacant lots or lots without a single-family home.
- ✗It does not override certain development agreements a city signed on or before May 6, 2026 — some master-planned communities may sit under older recorded terms.
What cities can still require
State law preserves meaningful local authority. A covered city may still:
- ▸Regulate unit size, height, lot coverage, setbacks, design consistency with the neighborhood, and window placement
- ▸Require owner occupancy (the owner must live in either the main house or the ADU)
- ▸Limit properties to one ADU
- ▸Require replacement parking when a garage is converted
- ▸Deny a detached ADU where utility access or capacity is inadequate
- ▸Prohibit rentals shorter than 90 days — which rules out nightly ADU rentals in many jurisdictions
What cities can no longer do
For qualifying lots after October 1, 2026, a covered city may not require a conditional use permit (a discretionary public-hearing approval) for a detached ADU located in a primarily residential zone, and state law caps how much on-site parking a city can demand based on the ADU's size. Cities also must provide a process for converting a legally built accessory structure — like an existing detached garage — into an ADU, subject to applicable standards.
Source: Utah Code §10-21-304 (S.B. 284, 2026 ); Provo City — ADU Eligibility Expansion .
Which Utah cities allow detached ADUs on smaller lots?
Several do — and that's exactly why the "11,000 square feet" headline can mislead. In this verified sample, published rules include no lot minimum in Salt Lake City's ADU ordinance, 7,000–10,000 sq ft minimums in several jurisdictions, and Draper's published 12,000 sq ft rule as a case to watch as cities update for the new state floor.
Detached ADU lot size requirements by Utah city (verified sample, July 2026):
| Jurisdiction | Detached ADU minimum lot size | Other key rules | Source |
|---|---|---|---|
| Salt Lake City | No minimum lot size in the ADU ordinance; allowed per the zone table | Detached ADUs capped at 1,000 sq ft; 17 ft base height (up to 24 ft with added setbacks); owner occupancy required, with limited exceptions; one ADU per lot; building permit required | SLC Code §21A.40.200 + ADU Handbook |
| Salt Lake County (unincorporated) | 7,000 sq ft (6,000 sq ft in the PC Zone) | 10 ft from rear line, 6 ft from main house; concrete slab foundation unless above a garage; water/sewer confirmation required; owner-occupancy affidavit | Salt Lake County ADU page |
| Millcreek | 8,000 sq ft | R-1 and Agriculture zones only; rear yard; 1,000 sq ft max; 5 ft side/rear setbacks; no separate utility meters; no ADUs on slopes over 30% | Millcreek ADU page |
| Murray | 10,000 sq ft | One ADU per lot; owner occupancy; short-term rental prohibited; setback, height, and size limits apply | Murray City ADU page |
| Farmington | 10,000 sq ft (detached prohibited below that) | Internal ADUs prohibited below 6,000 sq ft; detached unit must be subordinate to the main home's footprint; one added off-street parking stall | Farmington City Code §11-28-200 |
| Draper | 12,000 sq ft (published city rule — see note) | Rear yard only; owner occupancy; rentals of 30+ days; one extra parking space. Draper's published minimum sits above the new state floor — for qualifying 11,000+ sq ft lots, the state standard applies from October 1, 2026; watch for the city's implementing update | Draper City ADU page |
| Provo | 11,000 sq ft under the S.B. 284 expansion (plus a pre-existing ADU overlay in parts of the city) | Lot must have a single-family home; qualifying zone required; city permitting and rental dwelling licensing still apply; the city has published a parcel eligibility map | Provo ADU Eligibility Expansion |
| Lehi | In transition — city materials reference a prior 14,520 sq ft local standard and the new 11,000 sq ft state requirement | Verify the adopted ordinance before relying on any number; the code amendment was headed to City Council in mid-July 2026 | Engage Lehi — Detached ADU Code Amendment |
What we verified for this page (July 2026):
- ✓Utah's detached ADU state floor — 11,000 sq ft, effective October 1, 2026 — against the enrolled text of S.B. 284 and Utah Code §10-21-304
- ✓The local powers cities keep under state law (setbacks, size, height, coverage, design, owner occupancy, parking, utility adequacy, rental duration)
- ✓Published detached ADU lot-size rules for each jurisdiction in the table above, against official city, county, or municipal-code sources, each linked in its row
- ✓Permit and building-code dependency: no jurisdiction we reviewed allows a detached ADU without a building permit
Not verified here: every Utah city. Rows without a source and date are not published on this page. City rules change — always confirm current rules for your parcel before spending money.
Start with feasibility, then get a local cost estimate path if your property looks viable.
See What Kind of ADU Your Property May Support →Why a big-enough lot can still fail detached ADU feasibility
Lot size is one gate out of several. A parcel can clear 11,000 sq ft and still lose the project to setbacks, lot coverage, utility capacity, parking, easements, or private covenants. These are the checks that quietly kill detached ADU plans after homeowners have already paid for drawings — so run them first.
Setbacks and the buildable envelope
A setback is the required distance between a structure and your property lines. Detached ADUs typically carry their own setbacks — Salt Lake City requires a minimum of 3 ft from side and rear lines for detached units, while Millcreek requires 5 ft plus a 6 ft gap from the main house. On a narrow or shallow lot, the rectangle left over after setbacks may be too small for the unit you have in mind, no matter what the total square footage says.
Lot coverage and existing structures
Lot coverage is the share of your lot that buildings may occupy. Your house, garage, sheds, and covered patios all count against it. An 11,000 sq ft lot with a large home and a detached garage can have very little coverage allowance left — Salt Lake City and Millcreek both apply coverage limits on top of their 1,000 sq ft unit caps.
Utilities
A detached ADU needs water, sewer, and power routed to a new structure — the utility hookups. State law expressly lets cities deny a detached ADU where utility access or capacity is inadequate, and Salt Lake County requires written water/sewer availability confirmation before a permit is issued. Trenching distance, service upgrades, and meter decisions (some cities prohibit separate meters; others allow them) can swing project cost significantly.
Parking
The jurisdictions we verified generally require at least one added off-street space for the ADU — Salt Lake City waives its stall in specific cases, such as proximity to transit — and converting a garage usually means replacing the parking it held. State law caps how much parking a covered city can require based on ADU size, but "capped" is not "zero": a lot with no room for an added stall has a real problem.
Owner occupancy and rental duration
Owner occupancy means the property owner must live in either the main home or the ADU — Salt Lake City, Millcreek, Murray, Draper, and Salt Lake County all require it in some form. And state law allows cities to prohibit detached ADU rentals shorter than 90 days, so do not plan around nightly short-term rental income unless your city's ordinance explicitly allows it. Many prohibit it outright. See our ADU rental income guide for what long-term rental looks like in practice.
HOA covenants, easements, and older agreements
Recorded easements can carve unbuildable strips through the exact corner of the yard you planned to use. Private covenants and HOA rules may restrict detached structures even where the city allows them — and the state law does not override certain development agreements signed on or before May 6, 2026. These need parcel-specific review; no statewide page can clear them for you.
Sources: Utah Code §10-21-304; SLC ADU Handbook ; Millcreek ; Salt Lake County .
A practical read on your lot size
Use lot size to decide how hard to investigate — not as a yes/no permit answer. The smaller the lot, the more city-specific the answer becomes; the bands below are anchored to the verified rules above.
| Your lot size | Practical read |
|---|---|
| Under 7,000 sq ft | A detached ADU is a long shot in most of the jurisdictions we verified. An internal (basement) ADU is usually the better first question — internal ADUs don't carry the detached lot-size test. Converting a detached garage still counts as a detached ADU and follows detached rules. |
| 7,000–7,999 sq ft | Possible in some jurisdictions — unincorporated Salt Lake County's published minimum is 7,000 sq ft. Elsewhere, city-dependent. |
| 8,000–9,999 sq ft | Possible where minimums run lower — Millcreek's published minimum is 8,000 sq ft. Setbacks and coverage become the deciding factors. |
| 10,000–10,999 sq ft | Possible in cities like Murray and Farmington (10,000 sq ft each), but below the state floor — so if your city says no, the state law won't override it. Note: a standard quarter-acre lot (10,890 sq ft) lands in this band. |
| 11,000 sq ft or more | Worth a feasibility check in nearly any covered city from October 1, 2026. Not automatic approval — setbacks, coverage, utilities, and parking still decide the buildable reality. |
How to check your lot before paying for plans
Five checks, in order. Most take minutes; together they tell you whether design money is premature.
- 1Pull your real parcel size. Use your county assessor's parcel record — not a listing estimate or a guess from the fence line. Threshold cases are decided by exact square footage (remember: 0.25 acres = 10,890 sq ft).
- 2Confirm your jurisdiction. A Salt Lake City address, a Millcreek parcel, a Murray parcel, and an unincorporated-county parcel can sit within a few blocks of each other and carry four different lot-size rules. Your mailing address is not always your zoning jurisdiction.
- 3Confirm a single-family home sits on the lot, in a qualifying zone. The state floor only reaches lots that contain a single-family dwelling in a zone where single-family homes are permitted. Vacant lots and multi-family properties follow different rules.
- 4Eyeball the usable rear yard. Subtract setbacks, easements, slopes, and existing structures from your yard. If the remaining envelope can't hold the unit plus required parking, size on paper won't save the project.
- 5Run feasibility before design. Plans and engineering are the expensive step. A feasibility review that checks zone, lot size, setbacks, coverage, utilities, and parking against your actual parcel is the cheap step — do it first. See our Utah ADU cost guide for what the full project investment looks like.
Does a garage conversion or prefab ADU change the lot-size rules?
No project type lets you skip zoning, permits, setbacks, utilities, or building code. A garage conversion, a prefab unit, or a site-built backyard cottage changes the construction path and the budget — not the rules that decide whether your property qualifies.
Converting an existing detached garage
This is often the most practical detached path on tighter lots, because the structure and its setbacks already exist. State law requires covered cities to provide a process for converting legally built accessory structures into ADUs, subject to applicable standards — expect building, health, and fire code upgrades, and plan to replace the parking the garage provided if your city requires it.
Prefab and tiny-home-style units
A factory-built unit still needs a permitted foundation, utility hookups, and full code compliance, and it counts against the same lot-size, setback, and coverage rules as site-built construction. Compare prefab bids on the all-in installed cost — unit, site prep, foundation, utilities, delivery, and permits — never the base unit price alone.
Detached ADU feasibility checklist for Utah homeowners
- Jurisdiction confirmed (city vs. unincorporated county)
- Lot size pulled from the county parcel record
- Zoning district allows single-family dwellings
- Existing single-family home on the lot
- Usable rear-yard area after setbacks
- Lot coverage headroom with existing structures counted
- Easements checked on the plat/parcel record
- Slope and drainage workable
- Utility route and capacity plausible (water, sewer, power)
- Room for required parking (plus replacement if converting a garage)
- Owner-occupancy rule acceptable to you
- Rental plan matches local rental-duration rules (assume no nightly rentals unless your city says otherwise)
- HOA/CC&R restrictions reviewed
- Use case defined (family housing vs. long-term rental)
- Realistic budget range and timeline in mind
- Build path considered: garage conversion vs. prefab vs. site-built
If you checked most boxes — or you're not sure how to check some of them — that's exactly what a feasibility review is for.
A detached ADU may be possible on your lot — but lot size is only one part of the answer. Feasibility first, then costs, then builders.
Request a Utah ADU Feasibility Review Before You Pay for Plans →