ADU Rules in Clearfield, Utah

Clearfield occupies a unique and challenging position in the Davis County landscape: it sits directly adjacent to Hill Air Force Base, one of the U.S. Air Force's most active installations and the home of the F-35A Lightning II. The base's flight operations create substantial noise impacts and accident potential zones that cover significant portions of Clearfield's residential areas. For anyone considering an ADU in Clearfield, understanding the Hill AFB AICUZ program is as important as understanding Utah's statewide ADU law.

Utah Statewide ADU Law: HB 462 (2022) and SB 174 (2023)

Utah's landmark housing legislation applies throughout Clearfield. HB 462 (2022) requires municipalities to permit ADUs by right in residential zones — through ministerial (administrative) approval. SB 174 (2023) further reinforced these protections. Key provisions:

• ADUs are permitted by right in residential zones outside AICUZ-restricted areas
• The city cannot require owner-occupancy as a permit condition
• The city cannot restrict ADU size below 50% of the primary unit's floor area or 1,000 sq ft (whichever is less)
• Reasonable development standards remain in effect

Critical caveat: State ADU law provides baseline protections, but Clearfield's AICUZ overlay creates additional requirements — and potentially outright restrictions — for new residential construction in certain zones. AICUZ review is essential before investing in ADU design.

Hill AFB AICUZ: The Dominant Land Use Constraint

Hill Air Force Base is immediately adjacent to Clearfield, with its main runways running roughly north-south. The AICUZ (Air Installation Compatible Use Zone) program — a Department of Defense compatibility planning tool — establishes:

Noise Contours (DNL - Day-Night Average Sound Level):

• DNL 65–70 dB: Residential use is "normally compatible" with sound attenuation measures; ADUs may be permitted with required insulation, upgraded windows and doors, and mechanical ventilation
• DNL 70–75 dB: Residential use is "normally incompatible" — new residential construction including ADUs is strongly discouraged; may require special review
• DNL 75+ dB: Residential use is "clearly incompatible" — new residential dwellings are prohibited or face significant barriers

Accident Potential Zones (APZ):

• APZ-I (highest hazard, closest to runway ends): New residential construction is generally prohibited; ADUs would face the same restriction
• APZ-II (moderate hazard): New residential construction is discouraged and may be restricted depending on density

Clearfield's AICUZ exposure: Due to its location relative to Hill AFB's runways, Clearfield has more area within high-noise contours and APZ zones than many neighboring cities. This is not a hypothetical concern — it affects land use decisions for a significant portion of Clearfield's residential parcels.

Steps before designing an ADU in Clearfield:

1. Obtain your parcel's AICUZ noise contour (DNL level) and APZ designation — available through Hill AFB's AICUZ program at hill.af.mil or through Clearfield City Planning
2. If your parcel is in DNL 65–70, plan for sound attenuation measures in your ADU design
3. If your parcel is in DNL 70+ or an APZ, consult with Clearfield City Planning before proceeding — new residential construction may face significant restrictions
4. Document AICUZ status early, as it will affect both your design and lender/insurer requirements

Defense Depot Ogden Legacy

Clearfield was also the site of the Defense Depot Ogden (DDO) — a major military logistics facility that closed in the 1990s. The former depot site has been redeveloped, but some areas may have environmental legacy concerns. If your parcel is near former depot land, consult Clearfield City about any relevant environmental assessments.

Local Zoning and Permitted ADU Types (Outside AICUZ-Restricted Areas)

Outside the most restrictive AICUZ zones, Clearfield's residential zoning permits ADUs pursuant to state law. Both attached ADUs (basement apartments, garage conversions, internal conversions) and detached ADUs (backyard cottages) are recognized.

Typical local development standards (verify current code):

• Setbacks: Detached ADUs typically 4–5 ft from side and rear property lines
• Height: Detached ADUs generally limited to one story or 16–20 ft
• Parking: One additional off-street space may be required
• Sound attenuation: Additional insulation and window requirements in DNL 65+ zones

Seismic Considerations: Wasatch Fault

Clearfield sits within the Wasatch Front seismic zone. The Wasatch Fault runs along the mountain base east of the city, and Davis County is in Seismic Design Category D under the Utah State Construction Code. New ADU construction must meet IBC seismic provisions. Areas near the Great Salt Lake shoreline may have liquefiable soils.

Permit Process

1. AICUZ status determination: Highest priority step — check before spending on plans
2. Zoning verification at Clearfield City Community Development (clearfieldcity.net)
3. Building permit application with site plan, architectural plans, structural documentation, and AICUZ sound attenuation details if required
4. Plan review: Typically 2–4 weeks
5. Inspections: Foundation, framing, MEP rough-in, and final
6. Certificate of Occupancy upon passing final inspection

Community Development: clearfieldcity.net | Phone: (801) 525-2700 | 55 S. State St., Clearfield

Disclaimer: ADU regulations are subject to change. Utah's statewide ADU laws (HB 462, SB 174) establish the baseline, but Hill AFB's AICUZ program creates significant additional constraints for many Clearfield parcels. Always verify your parcel's AICUZ status and current zoning requirements with Clearfield City Planning before beginning any ADU project.