Multi-generational living is one of the fastest-growing housing demands in Utah, driven by aging parents, adult children returning home, and remote work flexibility. Utah’s 2021 ADU legislation (HB 82) requires most cities to allow internal accessory dwelling units in single-family zones, but external casitas, separate-entry mother-in-law suites, and rental usage face more variable rules. Buyers seeking multi-generational homes in Utah have more options than ever — if they understand which rules apply to which property.

What Utah HB 82 actually does

Utah’s 2021 ADU law requires most cities to allow internal ADUs in single-family zoned areas. An internal ADU is a separate living unit within an existing home — typically a basement apartment, attached unit with separate entry, or interior space converted to independent living.

Key requirements:

Owner must occupy the primary residence or the ADU
The home cannot have other rental units (typically one ADU per primary home)
ADU must meet building code (separate entrance, kitchen, bathroom)
Most cities cannot require additional parking beyond standard requirements

Where HB 82 applies

Most Utah cities follow HB 82. Some have additional restrictions:

Salt Lake City — allows both internal and external ADUs with permits
Murray, South Salt Lake — generally permissive
Most of unincorporated Salt Lake County — follows state law
Provo, Orem — internal ADUs allowed with conditions
Bountiful, Layton, other Davis County cities — variable, most allow internal ADUs

Where rules are stricter

Some cities have layered additional requirements:

Minimum lot size requirements
Owner-occupancy requirements (stricter than state law)
Permit fees
Limits on rental to non-family members

External ADUs vs internal ADUs

The distinction matters significantly:

Internal ADUs (mother-in-law suites)

Within the existing primary structure
Easier to permit under HB 82
Lower construction cost ($25K-$75K typical)
Less impact on neighborhood character

External ADUs (casitas, detached units)

Separate from primary structure (typically detached buildings)
Subject to additional zoning requirements
Higher construction cost ($150K-$350K typical)
More variable city-by-city rules
May require larger lot size, additional setbacks

When buying a home with an existing external ADU, verify the structure was legally permitted. Unpermitted “she-sheds” and “guest houses” that have been used as living units may not be legal — and may need to be removed or brought into code.

How lenders treat ADUs in financing

ADUs can affect your mortgage qualifications in helpful ways:

Rental income from existing ADU

Some lenders count actual or projected rental income from a legal ADU as qualifying income for your mortgage. The treatment varies:

FHA: Can count up to 75% of projected fair market rent
Conventional (Fannie Mae): Similar 75% counting if ADU is legal
VA: Less common but some lenders allow

This can substantially improve buyer purchasing power. A $1,500/month ADU rent counts as $1,125/month additional income for DTI calculation, supporting roughly $200,000 more in home price.

Mortgage limits

Standard single-family loan programs apply (no special multifamily classification). Loan limits are based on conforming or jumbo thresholds.

Appraisal considerations

Legal ADUs add appraised value
Illegal or unpermitted “ADUs” don’t add value and may be flagged as code issues

What buyers should verify before offering

Five non-negotiable checks for multi-generational homes:

1. Existing ADU legality

Get permit records from the city. An unpermitted unit may need removal or major rework.

2. Current zoning allows ADU use

Confirm with city planning department, not just real estate listings. Listing language doesn’t override actual zoning.

3. Separate utilities or sub-metering

For long-term multi-generational livability, separate or sub-metered utilities are valuable. Verify what exists.

4. Code compliance

Modern fire separation, egress windows, smoke detectors. Old “finished basements” may not meet current code as separate living units.

5. Owner-occupancy and rental rules

If you plan to rent the ADU, confirm city rules allow it. Some cities require owner-occupancy of one unit.

Best Utah neighborhoods for multi-generational homes

Several patterns identify ADU-friendly areas:

Salt Lake City and inner suburbs

Older established neighborhoods (Sugar House, Harvard-Yale, Avenues)
Many existing legal basement apartments
Generally permissive ADU rules

Larger lots in suburban areas

Holladay, Cottonwood Heights, Sandy bench
Lot sizes that accommodate external casitas
Established neighborhoods with mature trees

Newer master-planned communities (selective)

Some Daybreak phases allow casitas
Some Saratoga Springs developments
Check HOA rules in addition to city rules

Areas to research carefully

HOA-restricted communities (may prohibit even legally allowed ADUs)
Older mobile home parks (different zoning entirely)
Properties with “non-conforming use” status (legal but restricted on modification)

Tax implications

Multi-generational homes with ADUs have nuanced tax treatment:

Property tax

The home is typically assessed as a single property at residential rates. Adding a legal ADU usually increases assessed value modestly.

Income tax

ADU rental income is reportable income on Schedule E
Expenses (mortgage interest portion, depreciation, repairs) are deductible
Owner-occupied family use generally isn’t taxable income

Capital gains exclusion

Section 121 exclusion ($250K/$500K) applies to your primary residence portion. The ADU portion, if rented, has more complex treatment when sold.

Common buyer mistakes

Three patterns we see:

Trusting listing language over verification

“Mother-in-law suite” in a listing doesn’t mean it’s legal. Verify with city records.

Underestimating renovation costs

“This basement could easily be converted to an ADU” usually costs $40K-$80K minimum.

Ignoring HOA rules

Even where city rules allow ADUs, HOAs may restrict them. Read HOA CC&Rs carefully.

What to do next

If you’re considering a multi-generational home in Utah, three immediate steps:

Identify your specific needs — parent care, adult child, occasional guests, rental income
Research target cities’ ADU rules — they vary significantly
Get pre-approved with a lender experienced in ADU rental income treatment

Reach out to Andrew for guidance on multi-generational homes in your target area. We work with this buyer type regularly and know which properties have legal, code-compliant ADU setups versus which require additional work.

Search Utah homes for sale and filter for properties with basement apartments or accessory units.

Multi-generational living works well in Utah — when buyers do the homework. The rules vary, but the options are real. The right property in the right neighborhood serves multiple generations and often pays for itself through rental income or shared family expenses.

Buying a Multi-Generational Home in Utah: ADU and Casita Rules Explained