Millcreek ADU Builders: Compare Your Options, Check Your Lot, and Estimate Costs

Can You Build an ADU on Your Millcreek Property?

This is the first question every Millcreek homeowner asks, and the answer depends on four things: your zone, your lot size, which type of ADU you want, and whether you live on the property.

Most homes in Millcreek's residential neighborhoods sit in R-1 zones. If yours does, you're eligible. Agriculture-zoned properties qualify too. Anything else — commercial, multi-family, mixed-use — does not. (MKZ 18.71.030)

Here's the fast eligibility check:

If you checked every box, your property likely qualifies. If you can't meet the 8,000-square-foot threshold for detached, keep reading — internal and attached ADUs don't have that lot-size minimum.

How to check your zone: Visit the Millcreek zoning map or call Millcreek Planning & Zoning at 801-214-2700. Give them your address — they can confirm your zone and lot size in under two minutes. You can also email planner@millcreekut.gov.

Also check for easements. Your property deed or a title search will show any recorded easements. ADUs cannot be built within a recorded easement (MKZ 18.71.060(G)). If you have a utility easement running through your rear yard, that could affect where — or whether — a detached ADU can be placed.

Three Types of ADUs Allowed in Millcreek (Side-by-Side Comparison)

Millcreek allows three ADU types, and each one comes with its own rules, costs, and tradeoffs. Here's how they stack up:

Sources: Millcreek ADU page, MKZ 18.71. Cost ranges are planning-level estimates for the Salt Lake County market (2025–2026).

Which ADU Type Is Right for You?

Pick internal if you already have usable space — an unfinished basement, an unused portion of your home — and want to minimize cost. This is the fastest, cheapest path to a legal rental unit in most cases.

Pick attached if you want more square footage than your existing layout allows, or if your lot size rules out a detached build. An attached ADU lets a family member have their own entrance without being in a completely separate building.

Pick detached if you want maximum privacy and independence for tenants or family, you're prioritizing long-term rental income, and your lot is 8,000+ square feet with adequate rear yard space. This is the most expensive option, but it also adds the most value and commands the highest rents.

How Your Goal Should Drive Your Decision

If rental income is the priority, a detached ADU typically commands the highest rents because tenants value the privacy of a separate structure. But remember — you're limited to long-term tenants only (30+ days) in a detached unit. If you want the flexibility of short-term rentals, go internal or attached.

If multigenerational living is the goal, think about daily life. An aging parent who values independence but needs to be close? Detached is ideal — their own space, their own entrance, their own kitchen, steps away from you. A young adult child saving money? A basement conversion gives them independence at a fraction of the cost.

If budget is the deciding factor, internal conversions win hands-down. If you have an unfinished basement with decent ceiling height and exterior access on the side or rear, you could have a legal rental unit for $40,000–$80,000. That's a fraction of the $175,000+ for detached — and the payback through rental income is dramatically shorter.

If you want Airbnb income, go internal or attached. Millcreek prohibits short-term rentals in detached ADUs (MKZ 18.71.090(C)). If your entire financial model depends on Airbnb rates, detached won't work.

Millcreek ADU Requirements: Every Rule You Need to Know

Every rule cited here comes directly from Millcreek Municipal Code MKZ 18.71 (dated April 28, 2025) and the city's official ADU page. We've translated it into plain language. Always verify with Millcreek Planning & Zoning (801-214-2700) before starting your project — code can change.

Zoning and Eligibility

ADUs are only allowed in R-1 and A zones. The property must be owner-occupied — meaning you live there as your primary residence. The use must be single-family residential at the time you apply and any time after. You get one ADU per lot: one internal, one attached, or one detached — not a combination. (MKZ 18.71.030, 18.71.060(B))

Size Limits

A detached ADU can be up to the lesser of 1,000 square feet or the gross square footage of your existing main building, whichever is smaller. Total lot coverage in your zone may further reduce the maximum. (Table 18.71-2)

Internal ADUs are limited by your existing home's layout. Attached ADUs are governed by your zone's lot coverage requirements. (MKZ 18.71.070, 18.71.080(C))

Setback Requirements

Detached ADUs need a minimum of 5 feet from side and rear property lines, and at least 6 feet from the main building. For every inch of height above 14 feet, you need an additional inch of setback. (Table 18.71-2)

Attached ADUs follow the same setback rules as your primary dwelling — whatever your zone requires for side and rear yards. (MKZ 18.71.080)

Existing structure conversions cannot reduce existing setbacks. If a detached building is already close to a property line, it can potentially be converted through the Land Use Hearing Officer process if legally established. (MKZ 18.71.130(C))

Height Limits

Detached ADUs can be up to the lesser of 24 feet or the height of the existing main building. Above 14 feet, the additional setback requirement kicks in. Converting an existing nonconforming structure? You cannot increase its current height. (Table 18.71-2, MKZ 18.71.130)

Design Standards

Millcreek takes design seriously — and that's good news for your property value. The city built standards that ensure your ADU blends with your neighborhood:

• Exterior materials: Your ADU must incorporate at least one exterior material from your primary dwelling on a minimum of 20% of all facades. (MKZ 18.71.060(F))
• Color: Must match your primary dwelling's color on at least 50% of all facades.
• Roof: Pitched roof required unless your primary dwelling has a flat roof (then flat or pitched is fine).
• Windows near neighbors: Any window within 15 feet of an abutting property containing a single-household, twin home, or duplex must be fixed (non-operable) and translucent, or installed as a skylight. (MKZ 18.71.090(E))
• No second-story balconies on detached ADUs. (MKZ 18.71.090(H))
• Entrances, parking, and stairways within 15 feet of an abutting property must not be visible from that property — screening with fencing, dense landscaping, or positioning is required. (MKZ 18.71.090(F))
• Attached ADU entrance must not be visible from the public right-of-way. (MKZ 18.71.080(A))
• Interior/attached ADU exterior door must be on the side or rear of the residence. (Millcreek ADU page)
• Exterior lighting must be directed downward with light sources not visible from abutting properties. (MKZ 18.71.090(D))
• Exterior stairways and landings cannot encroach into required setbacks. (MKZ 18.71.090(I))

A good Millcreek ADU builder designs to all of these standards from day one. No surprises at inspection. No costly redesigns.

Why These Design Standards Actually Help You

These rules might feel restrictive at first glance, but they serve you in three ways.

First, they protect your property value. An ADU that matches your home's materials and colors looks intentional, not like an afterthought. Neighbors see a well-designed addition to the neighborhood, not a random structure that lowers their property values.

Second, they protect your relationship with neighbors. The frosted-window requirement, lighting rules, and entrance screening all address the privacy concerns that make neighbors oppose ADU projects. By designing to these standards, you're proactively addressing the objections before they become complaints.

Third, they give your builder a clear target. There's no ambiguity about what Millcreek expects. A builder who knows these standards can design around them efficiently — often incorporating them in ways that actually improve the ADU's appearance. For example, matching your home's siding and roof pitch creates a cohesive look that makes the ADU feel like it was always part of the property.

Parking Requirements

Every ADU requires at least one off-street parking stall. No ADU parking is allowed on the street. (Millcreek ADU page)

If you're converting your garage, you must: (1) replace the garage parking with at least one covered stall, and (2) add one additional off-street stall for the ADU. This is one of the most common sticking points. Plan parking into your site design before anything else.

Utility Requirements

Separate utility meters are prohibited. Your ADU must run on the same water, sewer, gas, and electrical as your primary dwelling. Secondary monitoring meters — to track usage for billing a tenant — may be allowed. Work with your utility providers on this. (MKZ 18.71.060(D), Millcreek ADU page)

Rental Rules

Long-term rentals (30+ days) are allowed for all three ADU types — internal, attached, and detached. You need an ADU compliance letter from Millcreek and a valid Millcreek business license. (Millcreek ADU page)

Short-term rentals (under 30 days) are allowed for internal and attached ADUs only, per the city's current ADU page. You need an ADU application plus a business license. Detached ADUs cannot be used as short-term rentals. (MKZ 18.71.090(C)) Verify current business-licensing and short-term-rental rules directly with Millcreek before underwriting any STR income — these rules can change.

You cannot sell an ADU separately. It cannot be subdivided or separated from your primary property. (MKZ 18.71.060(A))

Occupancy limits for attached and detached ADUs: two adults and any number of children. (MKZ 18.71.080(B), Table 18.71-2)

Separate Address

You can request a separate address for your ADU. This requires submitting a site plan review to Millcreek Planning & Zoning and paying associated fees. (MKZ 18.71.110)

Existing Structures and Nonconforming Buildings

Buildings permitted before September 17, 2021 that don't meet current ADU standards must go through a noncomplying structure application. (MKZ 18.71.130)

If you already have a guest house, you cannot add a separate detached ADU. You can convert the guest house to an ADU if it meets all detached ADU requirements. (MKZ 18.71.130(A))

Detached buildings that comply with all current requirements can be converted, provided setbacks aren't further reduced and the structure meets building and fire codes. Noncomplying buildings may go through the Land Use Hearing Officer process. (MKZ 18.71.130(C))

How Much Does It Cost to Build an ADU in Millcreek?

This is the question that keeps most homeowners up at night. We'll be as specific as we can, with the caveat that every project is different.

Cost Ranges by ADU Type

Methodology: These ranges reflect estimates from Utah-based ADU builders, Angi's national ADU cost data, and ADU Utah's published construction costs for Salt Lake County ($190–$250/sq ft for building implementation, plus $25,000–$75,000 for site prep, permits, and utility connections). Ranges reviewed Q1 2026. Your actual cost will vary based on site conditions, finishes, builder, and complexity. Get detailed estimates from at least two local builders before committing to a budget.

What's Included — and What's Not

Hard costs (85–90% of budget): Foundation, framing, roofing, plumbing, electrical, HVAC, insulation, drywall, flooring, kitchen, bathroom, exterior finishing to meet Millcreek's design standards.

Soft costs (10–15% of budget): Architectural design ($5,000–$15,000 for a detached ADU), engineering, Millcreek permitting fees, surveys, soil testing.

Often-missed costs to budget for:

• Utility connections from main house to detached ADU: $5,000–$25,000+
• Site preparation and grading: $1,500–$10,000 (more for sloped lots)
• Replacement parking (garage conversions): $2,000–$8,000
• Landscaping repair after construction: $2,000–$10,000
• Structural upgrades in older homes (conversions): varies widely
• Business license and inspection fees (if renting)
• Furnishing a rental unit: $5,000–$15,000

Why Smaller ADUs Still Cost a Lot

Every ADU — regardless of size — needs a foundation, a kitchen, a bathroom, plumbing, electrical, HVAC, and utility connections. Those fixed costs don't scale down with square footage.

That's why the most cost-efficient approach in Millcreek is often to build as close to the maximum allowed size as your lot supports. You're already paying for the expensive parts. The marginal cost of additional square footage is relatively cheap compared to the base.

A Practical Way to Think About Costs

Think of a detached ADU as building a very small house. Because that's what it is. It needs its own foundation, walls, roof, kitchen, bathroom, plumbing, electrical, and HVAC. The only thing it shares with your main house is the lot and the utility connection point.

That's why the floor for a new detached ADU is around $175,000 even at the smallest sizes. You can't build a kitchen, bathroom, and living space for less than that once you account for foundation, framing, mechanical systems, permits, and finishes.

Get at least two or three detailed estimates. Not ballpark ranges — line-item estimates that account for your specific site conditions. The spread between bids on a Millcreek ADU project can easily be $50,000–$80,000. Some of that difference is builder overhead. Some of it is how accurately they've assessed your site. You want the most realistic builder, not necessarily the cheapest.

What Moves Your ADU Cost Up or Down

Moves cost up: Sloped lots requiring retaining walls or extra foundation work. Long utility runs from the main house to the rear yard. High-end finishes (quartz countertops, custom cabinetry, premium appliances). Complex roof lines or multi-story designs that increase the height setback requirements. Nonconforming existing structures that need the Land Use Hearing Officer process. Tight site access that requires specialized equipment.

Moves cost down: Flat, accessible rear yard with short utility runs. Standard-grade finishes that still look great (LVP flooring, stock cabinetry, solid surface countertops). Simple single-story rectangular design. Existing utility connections near the build site. Design-build approach that reduces coordination costs between separate architect and builder.

Financing Your Millcreek ADU

Most Millcreek homeowners finance their ADU through one of these paths:

• Home equity loan or HELOC: Leverages the equity you've already built. Often the simplest route.
• Cash-out refinance: Replaces your current mortgage with a larger one and gives you the difference.
• Construction loan: Specifically designed for building projects. Can convert to a standard mortgage after completion.
• Personal savings: No interest, no lender requirements.

Because ADUs cannot be sold separately, traditional home-purchase loans don't apply. Talk to a lender familiar with ADU financing in Utah.

Is It Worth It? Rental Income and ROI for Millcreek ADUs

For most homeowners, yes — especially in Millcreek's market. But let's look at the numbers honestly.

Estimated Rental Income

Millcreek sits in one of the most desirable rental corridors in Salt Lake County — central to downtown SLC, close to the University of Utah, and near the Cottonwood Canyons. That location drives strong rental demand.

Estimated long-term rental rates for the Millcreek area (based on Salt Lake County rental market data for comparable units, reviewed Q1 2026):

• Studio/1-bed (400–600 sq ft): $900–$1,400/month
• 1-bed/2-bed (600–1,000 sq ft): $1,200–$1,800/month

Your actual rent depends on finishes, exact location, and market conditions when you list. These are planning-level estimates, not guarantees.

Simple ROI Scenarios

These are gross estimates before maintenance, taxes, insurance, and vacancy. Your numbers will be different. Use these for planning purposes, not underwriting.

Beyond the Spreadsheet

41% of ADU owners nationwide use them for family members, not rental income. The value of keeping your aging parent nearby instead of paying for assisted living, or giving your adult child an independent space while they save — that doesn't fit neatly in a payback table, but it's very real.

Millcreek's location, limited new housing supply (the city is largely built out), and Utah's population growth all support long-term demand for small, well-located rental units. A fully permitted, code-compliant ADU is an asset that appreciates while it pays you back.

What Makes Millcreek ADUs a Strong Investment

A few factors work specifically in Millcreek's favor:

Location. Millcreek is sandwiched between downtown Salt Lake City and the Cottonwood Canyons. It's close to the University of Utah, major employers, public transit, and world-class skiing. Renters want to be here.

Supply constraints. Millcreek is largely built out — there isn't much undeveloped land for new apartment complexes. Your ADU isn't competing with a flood of new construction. It's adding a scarce product to a market that has demand for it.

Code compliance as a competitive advantage. Millcreek's design standards, parking requirements, and permitting process create a natural barrier to entry. Not everyone will go through the effort. If you do, you're holding an asset that's harder to replicate — which supports both your rent and your resale premium.

Long-term flexibility. Use your ADU as a home office today. Convert it to a rental when you need income. House a family member when circumstances change. Sell the whole property at a premium when you're ready. A permitted ADU gives you options that a single-use property doesn't.

The bottom line on ROI: An ADU won't make you rich overnight. But it steadily builds equity, generates income, and gives you optionality that most homeowners don't have. Whether the payback period is 6 years (basement conversion) or 13+ years (detached new build), you're building something that works for you over time.

How to Build an ADU in Millcreek: Step-by-Step Process

The process is straightforward if you follow it in order. The Millcreek homeowners who hit delays are almost always the ones who jumped to design before confirming feasibility.

Realistic Timeline

The single biggest thing you can do to stay on the shorter end? Start with a builder who has navigated Millcreek's process before and knows exactly what the city expects in every submittal.

What Most Millcreek Homeowners Get Wrong About ADU Projects

We're going to be honest with you for a second, because it'll save you money.

Building an ADU in Millcreek takes longer and costs more than most people expect. The permitting process alone can run 1–3 months. Total project timelines of 9–12 months are common. A detached ADU is a six-figure investment. There's no shortcut around that reality.

But here's what we see over and over: the projects that blow budgets and timelines almost always started wrong. Wrong builder. Wrong sequence. Wrong assumptions.

The Mistakes That Actually Cost Money

The good news: Every one of these mistakes is avoidable with the right builder. A contractor who has already navigated Millcreek's process, who designs to the city's standards from day one, and who does a real site assessment before quoting — that builder saves you months and tens of thousands.

How to Choose the Right ADU Builder in Millcreek

Not all contractors are equal when it comes to ADUs, and not all ADU builders know Millcreek's specific requirements. Here's what to evaluate.

The Builder Checklist

1. 1. Have you built ADUs specifically in Millcreek? Not just Salt Lake County. Each city has its own code, review process, and planning staff. Millcreek experience matters.
2. 2. Are you a licensed general contractor in Utah? Verify at dopl.utah.gov.
3. 3. Can you show me completed ADU projects? Photos, addresses, and references from past Millcreek clients.
4. 4. Will you give me a detailed written estimate? Not a vague range. A line-item estimate for your specific site — including utilities, parking, and site prep.
5. 5. Do you handle design, permitting, AND construction? Design-build firms are often more efficient because the architect and builder coordinate on code compliance from the start.
6. 6. Do you know MKZ 18.71? Ask them to explain Millcreek's design standards. If they can't describe the material-matching, frosted-window, and entrance-screening rules, they haven't done enough Millcreek work.
7. 7. Will you commit to a timeline in writing? A project schedule with milestones, not "roughly 6–8 months."
8. 8. Do you carry general liability insurance and workers' comp? Non-negotiable.

Red Flags

• • No Millcreek-specific experience
• • Won't provide a written estimate before you commit
• • Pressure to sign quickly or large upfront deposit
• • Unfamiliar with Millcreek's current ADU ordinance
• • No portfolio of local ADU work

Questions to Ask on Your First Call

1. 1. "Walk me through the last Millcreek ADU you completed — from application to final inspection."
2. 2. "What's the most common reason Millcreek ADU permits get delayed, and how do you prevent it?"
3. 3. "How do you handle the material-matching and color-matching design standards?"
4. 4. "What do you budget for utility connections on a detached rear-yard ADU?"
5. 5. "Can I talk to a Millcreek homeowner you've built for?"

A confident builder answers these without hesitation. If they stumble, they might be excellent elsewhere — but you want someone who's been through Millcreek's process, not someone figuring it out on your project.

Design-Build vs. Separate Architect + Contractor

Both approaches work. But for ADUs specifically, design-build tends to be more efficient because the designer and builder coordinate on Millcreek's requirements from the start. There's one point of accountability for code compliance, budget, and schedule. And you avoid the common scenario where an architect designs something the builder can't build within budget, or that doesn't account for a Millcreek-specific design standard.

If you hire separately, make sure your architect has Millcreek ADU experience. The design standards (material matching, entrance screening, window treatment near property lines) are specific enough that a general residential architect may produce plans that need revision — and revisions cost time and money.

What a Good Builder Conversation Feels Like

The right builder will ask you more questions than you ask them on the first call. They'll want to know your lot size, your zone, what you want to use the ADU for, whether you've checked for easements, what your driveway situation looks like for parking, and what your budget range is. They'll be honest about what your property can and can't do before they try to sell you on a design.

If a builder leads with glossy renderings and monthly payment calculations before they've even looked at your lot, that's a sign they're selling a product, not solving your problem.

What Happens After Your ADU Is Built?

When Millcreek approves your ADU, a compliance notice is recorded at the Salt Lake County Recorder's Office. That notice runs with the property permanently — if you sell, the next owner inherits the ADU rights and obligations, including the owner-occupancy requirement.

You cannot sell the ADU separately. It's tied to the primary property. But a fully permitted, code-compliant ADU is a premium selling point — it's a legal income-producing asset that's already built, approved, and ready to rent.

If you're renting, remember that Millcreek requires a valid business license for all ADU rentals, with periodic building inspections to ensure the unit stays to code. Stay current on your license and address repairs promptly. Budget roughly 1–2% of the ADU's construction cost per year for ongoing maintenance — HVAC servicing, exterior upkeep, appliance replacement, and routine repairs. Your rental income will cover that many times over.

Finding tenants in the Millcreek area is typically straightforward given the location's desirability. Most ADU owners list on platforms like KSL Classifieds, Zillow Rental Manager, and Facebook Marketplace. A well-photographed listing with clear details about the space, parking situation, and utilities will attract interest quickly.

Managing the rental: For a single ADU on your own property, self-management is simple — you're right there. If you'd rather be hands-off, local Salt Lake County property management companies handle ADU rentals. Just make sure they understand Millcreek's business license and compliance requirements.

How We Research and Verify This Page

We believe you should know where our information comes from.

Official sources cited:

• Millcreek Municipal Code MKZ 18.71 — Accessory Dwelling Unit Standards (April 28, 2025 version)
• Millcreek ADU page — city's public FAQ and guidance
• Millcreek ADU Checklist
• Utah Code §10-21-303 (formerly §10-9a-530) — Internal ADU provisions
• Utah Code §10-21-304 — Detached ADUs (SB 284, effective October 1, 2026)

Cost data is sourced from Utah-based ADU builders, Angi's national ADU cost database, and ADU Utah's published construction cost data for Salt Lake, Davis, Weber, and Utah counties. Ranges were reviewed in Q1 2026.

Update policy: We review this page whenever Millcreek amends their ADU ordinance, and at minimum quarterly. The ADU code has been updated several times since the original 2021 ordinance. If you spot anything outdated, let us know.

Disclosure: Utah ADU Builders is a lead-generation and builder-matching resource. We connect Millcreek homeowners with local ADU builders. Builders are not paying to be ranked or listed on this page. When you request an estimate through our site, we connect you with builders who serve the Millcreek area and have experience with local ADU projects.

Frequently Asked Questions About Millcreek ADUs