Magna ADU Builders: Rules, Costs, and Whether Your Lot Qualifies
Yes — many Magna homeowners can build an ADU, but the type your lot allows depends on its size and zone. Magna became a city in 2024 and sets its ADU rules through Magna Municipal Code §19.42.030. Internal or attached units need a 6,000+ sq ft lot; detached units need 8,000+. Owner-occupancy is required, short-term rentals aren't allowed, and projects typically run $50,000–$400,000+ depending on type.
An ADU (accessory dwelling unit) is a second, self-contained home on the same lot as your house: a basement apartment, a unit attached to the home, or a detached backyard cottage. Each type triggers different rules in Magna, which is exactly why a builder quote is the second step, not the first.
Last verified: June 2026.
Magna ADU rules at a glance
| Question | Quick answer |
|---|---|
| Can you build an ADU in Magna? | Often yes — in eligible residential (R), agricultural (A), and Planned Community (PC) zones, if your lot meets the size, setback, and parking rules. |
| Who makes the rules now? | Magna City (a city since May 1, 2024). Land use, permits, and inspections are administered by the Greater Salt Lake Municipal Services District (MSD) under Magna Municipal Code §19.42.030. |
| Minimum lot size | Internal/attached: 6,000 sq ft. Detached: 8,000 sq ft (6,000 in a PC zone with approved design standards). |
| ADUs allowed per lot | One. |
| Parking | One extra on-site space for internal/attached; two for detached; replace any spaces a garage conversion removes. |
| Owner-occupancy | Required — you must live in either the main home or the ADU. |
| Occupancy cap | No more than four adults, or two adults plus their minor children. |
| Short-term rental (Airbnb) | Not allowed; rentals must be 30+ consecutive days. |
| Detached height | No taller than your existing home. |
| Water sign-off | Written confirmation from your water provider (Magna Water District for most Magna properties) is required before a permit. |
| Typical cost (estimate) | ~$50k–$120k (basement) up to ~$200k–$400k+ (detached new build). |
| Smartest first step | Confirm feasibility before asking builders for bids. |
Who we are
Utah ADU Builders is a Utah-focused ADU planning, feasibility, and builder-matching resource. We are not Magna City, the Municipal Services District, Magna Water District, a law firm, lender, architect, engineer, or licensed contractor. We may earn compensation when homeowners request a feasibility review or are connected with local professionals. That compensation does not change how we explain Magna's ADU rules, cost ranges, feasibility factors, or permitting process.
Start with property fit, ADU type, parking, and a realistic cost path before asking builders for bids.
Can you build an ADU in Magna?
Often, yes. Magna's code allows internal, attached, and detached ADUs in its eligible residential (R), agricultural (A), and Planned Community (PC) zones, subject to lot size, parking, setbacks, owner-occupancy, and permitting. Whether your property qualifies comes down mostly to your zone, lot size, and whether there's room for the unit and its parking.
First, the thing most older guides get wrong: Magna is its own city now
Magna spent decades as an unincorporated part of Salt Lake County, then became a metro township in 2017, and officially became a city on May 1, 2024 under Utah's H.B. 35. That matters because a lot of ADU content still treats Magna as "just county land that follows county rules." It doesn't. Magna now has its own municipal code, and it contracts with the Greater Salt Lake Municipal Services District (MSD) for planning, zoning, building permits, inspections, and business licensing. The ADU standards are in Magna Municipal Code §19.42.030 — that's the document a Magna-savvy builder has read.
Match your idea to the right ADU type
- Internal ADU (IADU):a separate unit created inside your existing home — most often a basement apartment.
- Attached ADU (AADU):a unit attached to the house, usually built as an addition.
- Detached ADU (DADU):a standalone backyard structure — a "cottage," "casita," or tiny-home-style unit on its own foundation.
- Garage conversion:turning an existing garage into a livable unit (treated under the internal/attached or detached rules depending on the structure).
A "tiny home" can qualify as a detached ADU in Magna, but only if it meets the detached-ADU rules below — including a permanent foundation. A unit on wheels or a temporary/portable structure does not clear that bar, so don't treat prefab or tiny-home marketing as a shortcut around permits.
One more piece of context: the 2026 state law
Utah's SB284 (2026) requires cities of 5,000 or more residents to allow detached ADUs on lots of at least 11,000 square feet, with compliant policies in place by fall 2026 — though cities may choose to permit them on smaller lots. Magna already does: its own code permits detached ADUs on lots as small as 8,000 square feet. So in Magna, your local code is what governs, and it's more generous than the statewide floor.
The fastest "no" signals
A Magna ADU usually won't pencil out — or won't be permitted as designed — if any of these are true:
- ✗The lot is below the size threshold for the ADU type you want (6,000 sq ft internal/attached; 8,000 sq ft detached).
- ✗There's no room to add the required parking (one space for internal/attached, two for detached).
- ✗A garage conversion would remove required parking and you can't replace it on-site.
- ✗Setbacks, utility easements, or lot-coverage limits leave no buildable spot.
- ✗You don't plan to live in the main home or the ADU (owner-occupancy is required).
- ✗Your goal is nightly/short-term rental income (not allowed).
- ✗You want to sell the ADU separately someday (not allowed).
Magna's ADU rules every project has to meet
A serious Magna ADU plan starts with the rules, not a price-per-square-foot. The rules below come straight from Magna Municipal Code §19.42.030 and decide what's buildable, what it costs, and what a builder should verify before quoting.
Lot size and where the ADU can sit
Internal and attached ADUs can only be built on lots of 6,000 sq ft or more. Detached ADUs require 8,000 sq ft or more (with a 6,000 sq ft pathway in a Planned Community "PC" zone if approved design standards are part of a development agreement). You're allowed one ADU per lot, and no ADU is permitted on a townhome, a multi-family PUD, another attached unit type, or any lot that can't satisfy parking, setback, and lot-coverage rules.
Setbacks, height, and foundation for detached ADUs
A setback is the minimum distance a structure must sit from a property line. Magna's standards for a new detached ADU:
| Standard | New detached ADU in Magna |
|---|---|
| Side yard setback | At least 5 ft |
| Rear yard setback | At least 5 ft |
| Distance from the main house | At least 6 ft |
| Offset behind the front of the house | At least 10 ft behind the front façade |
| Placement | Not in the front yard or corner-lot side yard |
| Height | No taller than your existing home |
| Foundation | Permanent foundation — not on a basement, piers, or any temporary/wheeled base |
Public utility easements can push setbacks farther than the minimums. A detached ADU has to keep your property looking like a single-family home, with proper roof and stormwater drainage. Converting an existing accessory structure follows the setback rules that were in place when that structure was originally built.
Parking
On top of the parking your home already requires, plan for:
- One on-site space for an internal or attached ADU.
- Two on-site spaces for a detached ADU.
- Replacement parking for the main house if a garage conversion removes existing required spaces.
Parking is the quiet dealbreaker for a lot of garage-conversion plans, so it's worth checking first.
Owner-occupancy, occupancy limits, licensing, and the recorded notice
- Owner-occupancy:you (the owner) must live in either the main home or the ADU. There's a limited exception of up to two years for documented medical, military, or religious reasons, with an on-site manager designated — and you can't collect rent on the unit you'd normally occupy.
- Occupancy cap:an ADU may house no more than four adults, or two adults plus their minor children.
- Building permit:required before you build or convert. Conversions must meet safety requirements like egress windows with window wells, adequate HVAC, and climate control.
- Water sign-off:before a permit is issued, you must submit written confirmation from your water provider — Magna Water District for most Magna properties — that the unit meets water-service requirements.
- Business license:required before you rent the ADU, and maintained for as long as it's rented.
- Recorded notice:once approved and licensed, a Notice of Accessory Dwelling Unit is recorded against your property's title. When you sell, the new owner re-signs the owner-occupancy affidavit and re-authorizes the ADU.
Rental and ownership limits
No short-term rentals. A short-term rental is a stay under 30 days (think nightly Airbnb/VRBO). Magna-approved ADUs may only be rented for 30 consecutive days or more.
Can't be split off. A Magna ADU may not be separately metered, sold, or subdivided from the main home. It stays part of a single-family property.
One honest gap worth flagging: Magna's code controls ADU size mainly through lot coverage, the "no taller than the home" height rule, and building code — rather than a single headline square-footage cap that applies everywhere. The exact size your lot can support is a feasibility question, not a number you can assume from a guide.
Is your Magna property likely a fit?
The fastest way to know if an ADU is realistic on your lot is to run it against the same handful of filters a planner and a good builder will use. Most lots that clear the size threshold and have usable backyard, basement, or garage space are workable; the common stoppers are undersized lots, tight setbacks, and parking.
Magna ADU lot-fit checklist — answer each honestly:
- Single-family lot in an eligible zone? ADUs aren't allowed on townhomes, multi-family PUDs, or attached unit types.
- Lot ≥ 6,000 sq ft (internal/attached) or ≥ 8,000 sq ft (detached)? This is the first hard filter.
- Room for the unit after setbacks? For detached: 5 ft sides/rear, 6 ft from the house, 10 ft behind the front of the house, and out of the front/corner side yard.
- Space for the added parking? One space (internal/attached) or two (detached) — plus replacements if you're converting a garage.
- Will you live in the main home or the ADU? Owner-occupancy is required.
- Will the household fit the occupancy cap? No more than four adults, or two adults plus their minor children.
- Is long-term rental (30+ days) acceptable? If you're banking on nightly rentals, a Magna ADU won't deliver that.
- Can your water provider serve a second unit, and can power/sewer reach it? Utility distance and capacity are real cost and feasibility drivers.
If you checked most of these "yes," you likely have a workable project worth pricing. If a few are "no" or "unsure," that's exactly what a feasibility review is for — it's far cheaper to find out now than after you've paid for plans.
Start with property fit, ADU type, parking, and a realistic cost path before asking builders for bids.
Which ADU type makes the most sense in Magna?
The most practical type depends on what your property already has. If budget is the priority, a basement or garage conversion is usually cheapest because the shell exists. If you want real separation for family or a long-term tenant, a detached cottage is often worth the higher cost — if your lot qualifies.
| ADU type | Best for | Main thing to watch |
|---|---|---|
| Basement / internal | Existing basement space, housing family, long-term rental | Egress, ceiling height, separate entrance, parking, code upgrades |
| Attached addition | More living space without a fully separate building | Foundation and roof tie-in, setbacks, utility extension |
| Garage conversion | An underused garage and somewhere else to park | Replacing required parking is often the dealbreaker |
| Detached cottage / tiny-home-style | The most privacy and separation for a long-term tenant, family, or multi-generational living | Needs 8,000+ sq ft, utility runs, setbacks, permanent foundation, highest cost |
A note on detached and tiny-home-style units
For homeowners whose lots can support a detached ADU, a prefab or tiny-home-style unit can be worth comparing against fully site-built construction. Utah ADU Builders has a partnership with Nest Tiny Homes, a Utah builder that designs and builds custom detached, attached, and garage-conversion ADUs across Salt Lake County. To be clear: that partnership is one option to weigh after feasibility — it does not mean a Nest unit is automatically approved, the cheapest choice, or the right fit for every Magna property, and we don't describe it as "pre-vetted." A detached unit still has to satisfy Magna's lot-size, setback, parking, foundation, and utility rules, and you can confirm any builder's license yourself through the Utah DOPL license-lookup tool. Feasibility comes first, then product comparison.
What does an ADU cost in Magna?
There's no honest single price. As a planning range, ADUs in the Salt Lake County area in 2026 run from about $50,000 for a straightforward basement conversion to $400,000+ for a detached new build — but your real number depends on type, existing structure, utilities, finishes, and site conditions. Use the ranges below to budget, not to bid.
| ADU type | Typical all-in cost (2026 estimate) | Rough $/sq ft | Why it varies |
|---|---|---|---|
| Basement / internal conversion | $50,000–$120,000 | $80–$150 | Cheapest when plumbing is already roughed in; egress, entrance, and code upgrades drive cost |
| Garage conversion | $80,000–$150,000 | $100–$200 | You already have the shell; parking replacement and utility work add up |
| Attached addition | $150,000–$250,000 | $200–$350 | Shares some structure and utilities with the house |
| Detached new build | $200,000–$400,000+ | $250–$400+ | Essentially a small new house: foundation, full utility runs, finishes |
How we estimate this: these ranges reflect 2026 cost reporting from multiple Utah ADU builders and market sources, cross-checked against our Utah ADU cost guide and last reviewed in June 2026. They cover design, permits, standard sitework, and construction, but not property-specific surprises like long utility runs, panel upgrades, difficult soil, or premium finishes. They are planning estimates for the region, not quotes for your lot.
What pushes a Magna number up or down: the ADU type; the condition of the existing structure; how far utilities have to run; whether your electrical panel needs upgrading; parking and driveway work; setbacks and easements; soil, slope, and drainage; design and engineering; finish level; and the permit path.
How Magna charges for ADU permits
Magna doesn't charge a single flat "ADU fee." Building permit and plan-check fees are calculated from your project's construction valuation, so they scale with the size and value of the build — a basement conversion sits at the low end, a ground-up detached unit at the high end.
| Fee | How Magna calculates it |
|---|---|
| Building permit | Based on your project's construction valuation (standard ICC valuation tables) — scales with size and value |
| Plan check (residential) | 40% of the building permit fee |
| Mechanical / plumbing / electrical permit | $70 base for one system, plus $20 per additional fixture or appliance |
| Land use review | $110 |
| State surcharge | 1% of the permit fee |
| Impact fees — internal ADU | None; internal ADUs built inside an existing home are exempt under Utah Code §11-36a-202 |
| Water / sewer connection | Varies by project; set by Magna Water District |
Per Magna's current building fee schedule (administered by the MSD); ICC valuation tables update periodically, so confirm current amounts during feasibility. An impact fee is a one-time charge a city collects to offset a new unit's demand on roads, sewer, and parks. For a typical ADU, the building-permit-and-plan-check package usually lands in the low thousands of dollars, with larger detached builds costing more.
How long does it take, and what's the permit path?
As a general planning window — not a Magna permit guarantee — expect roughly 3–8 months for a basement or garage conversion and 6–18 months for a detached new build, including design, plan review, and construction. Actual timelines vary with site complexity, how complete your plans are, and how many revision rounds the reviewer requests.
- 1Confirm feasibility. Lot size, ADU type, parking, setbacks, utilities, and water service. This is where most bad surprises get caught.
- 2Design and engineering. Floor plan, site plan, and (for detached units especially) stamped/engineered drawings.
- 3Water confirmation. Get your water provider's written sign-off — it's required before a permit can issue.
- 4Submit to the MSD. Plans go to the Greater Salt Lake MSD with your owner-occupancy affidavit and supporting documents. Expect a review period and, often, at least one round of corrections.
- 5Permit issued → build → inspections. Construction proceeds under inspection.
- 6License and record. Get a business license before renting; the Notice of ADU is recorded against your title.
Because each step depends on the one before it, a clean feasibility review and complete plans are the biggest levers you have on timeline.
How to compare Magna ADU builders before you ask for bids
The right Magna ADU builder isn't just the cheapest contractor — it's one who can explain the likely ADU path, the local rules, who's responsible for design and permits, and what's excluded from the price before you rely on a number. The most common way homeowners get burned is a low square-foot quote with no scope behind it.
Verify the license yourself. Utah generally requires a licensed contractor to do this kind of work, and you can confirm any contractor's license through the Utah Division of Professional Licensing (DOPL) license-lookup tool. We don't describe matched professionals as "verified" or "pre-vetted" unless the criteria are shown — instead, we encourage you to verify the license and insurance directly.
A quick builder scorecard
| What to check | Green flag | Red flag |
|---|---|---|
| Utah license | Verifiable through DOPL | Vague or won't share details |
| ADU-type experience | Talks specifically about internal vs. detached vs. conversion issues | Treats every ADU the same |
| Magna rule awareness | Mentions lot size, parking, setbacks, owner-occupancy, 30-day rental rule | Quotes a price with no feasibility questions |
| Design & permits | Clear on who handles drawings, engineering, and MSD submittals | "You deal with the city" |
| Scope detail | Itemized inclusions and exclusions, especially utilities | One-line quote |
| Promises | Doesn't guarantee approval, income, or value | Guarantees permit approval, rental income, or a fixed appraisal bump |
Questions worth asking before a bid:
Have you built this ADU type before? Who handles design, engineering, and permit corrections? What's included for utilities and parking? What's excluded? What could trigger a change order? Can I verify your license and insurance?
Start with property fit, ADU type, parking, and a realistic cost path before asking builders for bids.
When a Magna ADU may not be worth it (yet)
It's worth saying plainly: not every Magna property is a good ADU candidate, and a feasibility review sometimes ends in "not now." Reconsider — or expect a reshaped project — if:
- ✗Your lot is below the size threshold for the ADU type you want.
- ✗You can't add the required parking, especially for a garage conversion.
- ✗Setbacks, easements, or lot coverage leave no buildable footprint.
- ✗Utilities or water service would need expensive upgrades to reach a second unit.
- ✗Your plan depends on short-term rental income — Magna doesn't allow it for ADUs.
- ✗You want a hands-off investment you won't live near — owner-occupancy rules out an absentee setup.
If that's your situation, the smart move isn't a builder bid — it's a feasibility check that tells you whether a different ADU type, a smaller scope, or a different timeline makes the project work.
Frequently asked questions
What we verified
We built this page from primary and official sources, checked in June 2026:
- Utah state ADU law — internal-ADU permitted-use framework (Utah Code §10-21-303), the internal-ADU impact-fee exemption (Utah Code §11-36a-202), and the 2026 detached-ADU law (SB284).
- Magna's ADU rules — Magna Municipal Code §19.42.030 (Title 19), administered by the Greater Salt Lake Municipal Services District.
- Magna's status and service structure — Magna's conversion from metro township to city (H.B. 35, effective May 1, 2024) and its contracted planning, permitting, and licensing through the MSD.
- Permit fees — Magna's current building fee schedule (valuation-based building permit and plan-check fees, trade-permit and land-use fees, state surcharge).
- Water authority — Magna Water District as the local water and sewer provider whose sign-off is required before a permit.
- Cost inputs — multiple 2026 Utah ADU builder and market sources, presented as labeled regional estimates, not Magna-specific quotes.
- Builder verification — Utah DOPL license lookup for confirming contractor licensing.
Magna's ADU rules, fees, and permit processes can change. This page summarizes sources checked in June 2026 and should be reverified before you finalize design, permitting, financing, or construction.
Check your likely ADU type, the local rules that affect your lot, and a realistic cost path before comparing builder options.
Request a Magna ADU feasibility review →Start with property fit, ADU type, parking, and a realistic cost path before asking builders for bids.
Sources
- Magna Municipal Code, Title 19 §19.42.030 — Accessory Dwelling Unit standards
- Greater Salt Lake Municipal Services District — Magna planning, permits, and inspections
- Magna City — city services and structure
- Magna building fee schedule (MSD)
- Magna Water District — water and sewer service
- Utah Property Rights Ombudsman — Accessory Dwelling Units (Utah Code §10-21-303; §11-36a-202)
- Utah Legislature — SB284 (2026), detached accessory dwelling units