Basement Apartments & ADU Rules in Eagle Mountain and Saratoga Springs

Two quick terms before we dig in. ADU stands for accessory dwelling unit. A self-contained second living unit on a single-family property. A basement apartment is the most common kind. IADU is short for internal ADU. One inside the existing house, like a basement apartment, as opposed to a detached structure (like a casita) out in the yard. Saratoga Springs uses the IADU term in its zoning code; Eagle Mountain just uses ADU.

The two cities at a glance

Eagle Mountain ADU rules (EMMC 17.70)

So if you're thinking about a basement apartment in Eagle Mountain, here's the layout of the actual approval process.

An ADU permit is required from the Eagle Mountain Planning Division in addition to the building permit. The planning approval and the building permit run on parallel tracks. The building permit covers the construction work; the planning approval confirms the ADU itself is allowed at that address with that configuration. You can read the full ordinance at EMMC Chapter 17.70.

A basement ADU must have a separate exterior entrance located on the side or rear of the building. The front entrance can't double as the ADU entrance. This is a long-standing Eagle Mountain rule meant to keep the primary house reading as a single-family residence from the street.

An internal connection to the primary dwelling is not required. A lot of homeowners choose to keep an interior door connecting the basement ADU to the upstairs (often locked from both sides), which makes the unit easier to use as guest space or in-law space when not rented. The code doesn't require it either way.

For detached ADUs (cottage homes, casitas, guest houses on the same lot), Eagle Mountain has its own rules: minimum 400 sq ft, maximum 1,200 sq ft, maximum 2 bedrooms, lot must have at least 70 feet of street frontage, and the detached ADU must sit at least 6 feet from the primary dwelling. This page is focused on basement (internal) ADUs. Detached ADUs are a different conversation.

Here's something that catches people: EMMC 17.70 is explicit that any homeowner who owns an unpermitted ADU, or who previously finished a basement without a permit and now wants to legalize it as an ADU, has to obtain all required permits (including a retroactive basement permit for the previously unpermitted work) and pay all applicable fees before ADU approval. The city does not back-date approvals.

ADU permits transfer with the property as long as the ADU remains in compliance. A new owner inherits the existing approval. If they change the configuration, they re-apply.

Saratoga Springs internal ADU rules (Chapter 19.20)

Saratoga Springs took a different approach. Rather than allow ADUs everywhere with conditions, the city's Land Development Code Chapter 19.20 divides every residential property in the city into one of three IADU classifications, visible on a published interactive city map:

• IADU Allowed — internal ADUs are permitted as of right, subject to the building code and the standard requirements below.
• IADU Potential — internal ADUs may be allowed with additional approvals or conditions specific to the parcel.
• IADU Prohibited — internal ADUs are not allowed at this address. Roughly one-fifth of Saratoga Springs residential area falls in this zone as of the most recent published data. The state cap is 25%. Check the live IADU map for current boundaries.

Before designing an ADU in Saratoga Springs, check the IADU map. The map is the canonical source. Articles, second-hand information, and "what my neighbor did" are not reliable substitutes. A property in the Prohibited zone cannot have an internal ADU regardless of how you design the finish.

External detached ADUs are not allowed in Saratoga Springs at all. This is the major structural difference from Eagle Mountain, which does allow detached units. Saratoga Springs is internal-only.

Saratoga Springs IADU requirements

• Minimum lot size6,000 sq ft
• Separate exterior entranceRequired (per setbacks)
• Separate living areas (kitchen, bath, sleeping)Required
• Additional paved off-street parking1 space, min 9'×18'
• Parking locationBehind front setback line
• IADU address suffix"Unit B"
• Occupancy permit (pre-occupancy)Required
• Pre-occupancy fine$100 + $30/day

The $100 plus $30 a day fine for occupying before the Certificate of Occupancy is issued is written directly into the building permit application itself — it's not a buried rule. The math doesn't work in your favor at $30 a day, because a C of O delay can be weeks if there's a punch-list item outstanding. Don't move tenants in until final inspection passes.

What Utah state law says (Sections 10-21-303 and 17-80-303)

Two Utah Code sections set the statewide framework for internal ADUs. Utah Code §10-21-303 covers municipalities; §17-80-303 covers counties. The core rules from state law that supersede or constrain local code:

• Internal ADU rentals are permitted by state law if they do not violate local land use, building, health, or fire codes.
• Internal ADUs must be within the existing footprint of the primary dwelling at the time the IADU is created. A basement finish converts existing space and qualifies. An addition that expands the footprint does not.
• The primary dwelling must be a detached single-family home, and must be owner-occupied. You can't rent out the upstairs and the basement to separate tenants and keep the structure as a single-family designation.
• Municipalities may cap the percentage of residential area where ADUs are prohibited at 25%. Saratoga Springs sits at roughly one-fifth. Eagle Mountain doesn't use the zone-classification approach.

What an ADU-grade basement finish costs

An ADU-grade basement finish (separate exterior entrance, kitchen or kitchenette, fire-rated separation where required, additional inspections) typically runs $90,000 to $120,000 or more in Utah. The premium over a standard $42K to $58K basement comes from five line items:

• Kitchen / kitchenette installation$12,000 – $25,000
• Separate exterior entrance construction$8,000 – $20,000
• Fire-rated separation where required$2,000 – $6,000
• Additional egress (per added bedroom)$3,000 – $7,500 each
• Ejector pump (often required for full kitchen)$2,000 – $5,500
• Additional inspections, planning approval$500 – $1,500
• Higher-grade fixtures (rental-durability)$3,000 – $8,000

The separate exterior entrance is the most variable line. If the basement has a walkout configuration where the rear yard slopes below the basement floor, the entrance is straightforward — a door cut into the existing exterior wall. If the basement is fully below grade, the entrance requires an exterior stairwell well, which means foundation excavation, retaining walls, drainage, and the stair itself. A $15K to $20K project on its own. Full cost guide here.

Local rent expectations in 2026

Open-market basement-apartment listings in Saratoga Springs in early 2026:

• $1,250 per month plus utilities — 2-bedroom, 1-bath basement, around 1,300 sq ft, separate entrance, parking.
• $1,500 to $1,750 per month — 2-bedroom, 1-bath basement with in-unit laundry and updated finishes.
• $1,800 to $2,000 per month — 3-bedroom, 2-bath basement with in-unit laundry, full kitchen, separate entrance.

Rents vary with proximity to Saratoga Springs amenities (the lakefront, the schools, the commercial corridor), with the size and quality of the kitchen, and with whether utilities are included or paid separately. Eagle Mountain rents run slightly lower on the same basement configuration because of the longer commute to the I-15 corridor.

For most homeowners running the rental math, a 2-bedroom basement ADU finished at $90K to $100K and rented at $1,500/month cashflows reasonably after debt service and expenses. A 3-bedroom unit at $110K to $120K renting at $1,800 to $2,000 cashflows better. The bigger driver of return is occupancy stability, not the rent number.

HOA restrictions on basement apartments

Worth knowing before you design: HOAs can prohibit basement ADUs even when the city allows them. State law and city zoning set the floor; HOAs can add restrictions on top.

So if your neighborhood is governed by an HOA, read the CC&Rs before designing. The relevant clauses are usually under "single-family occupancy," "rental restrictions," or "ADUs." If the CC&Rs prohibit ADUs, that prohibition stands regardless of which Eagle Mountain or Saratoga Springs zone you're in. You'd be trying to get HOA approval for an exception, and most HOAs deny those.

Already finished without a permit? How to legalize

Here's the situation a lot of homeowners are in. Previous owner finished the basement without pulling permits. Now you want to legalize it, maybe even rent it as an ADU.

The path exists, but the order matters. The city will require you to retrospectively permit the basement-finish work first. This often means demolishing finish materials to expose framing for inspection. Then you apply for the ADU approval on top.

The total cost is meaningfully higher than doing it in the right order originally. Budget for the demolition, the permit, the inspections, and the re-finish. Probably $15K to $30K depending on how much has to come down to satisfy the inspector.

If you're considering this, call (801) 555-0184 before doing anything. The team has walked through this process more than once and can tell you what the inspector will actually want to see.

Common questions about basement ADUs