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Accessory Dwelling Unit (ADU) Permit in Unincorporated Natrona County, Wyoming

Required for construction of an ADU on a residential property in unincorporated Natrona County. ADUs are expressly defined and regulated as a Permitted (P) accessory use in the Urban Agricultural (UA), Mountain Residential 1 & 2 (MR-1/MR-2), Suburban Residential (SR), Rural Residential (RR), and Urban Residential (UR) zoning districts under the Natrona Next Zoning Resolution § 4.11.05(A). Built under the standard county Building Permit process once zoning standards are confirmed with Planning.

Verified 2026-07-01 · Source

When you need this permit

  • Zoning eligibility: ADU must be an accessory use to a legally permitted single-unit residential use in a district where ADUs are listed as Permitted (Table 4.02, districts include UA, MR-1, MR-2, SR, RR, UR) — confirm with Natrona County Planning Department before applying for the building permit
  • Number: One (1) ADU permitted per lot as accessory to a legally permitted single-unit residential use; in the UR district, the lot must be a minimum of 2 acres
  • Density in agricultural/mountain districts is expressed per-acre: e.g. UA and MR-1 allow 1 ADU per 10 acres (1 exempt ADU for agricultural-tax-status properties per 10 acres); MR-2 allows 1 ADU per 5 acres; SR and RR allow 1 ADU per lot
  • Setbacks: a detached ADU must comply with the zoning district's required (principal or accessory, as applicable) setbacks; an attached ADU must comply with principal building setbacks for its district
  • Height: an ADU must NOT exceed the height of the primary dwelling
  • Size: an ADU must not exceed 50% of the primary dwelling's square footage OR 1,000 gross square feet of habitable floor area, whichever is SMALLER
  • Occupancy: the property owner (title holder or contract purchaser) must occupy the principal dwelling as their permanent residence — owner-occupancy of the primary unit is mandatory
  • Use restriction: ADUs may not be sold separately from the primary residence, and must maintain architectural consistency with the primary dwelling
  • Once zoning compliance is confirmed, the ADU is built under the standard Natrona County Building Permit Application (select New Construction or Addition, per whether attached or detached) — plus separate Electrical, Plumbing, and Mechanical permits as applicable

Required documents

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Fee schedule

Building Permit Fee — valuation-based (same table as new construction)Natrona County Permit Fees, Resolution No. 45-20 — an ADU is charged under the same combined valuation-based building-permit fee schedule as any other new residential construction; no separate ADU fee line exists.
$70 (valuation $0–$2,500) up to $905 plus $9.24 per additional $1,000 over $98,000

Review timeline

Plan reviewTypical estimate — confirm current times with the Unincorporated Natrona County building department
~5–15 business days

How long did your Accessory Dwelling Unit (ADU) Permit permit actually take in Unincorporated Natrona County?

Anonymous — one question, no email. Answers are combined and only shown once at least 5 people have reported.

Inspection process

  1. 1

    Footing / Foundation

    Before concrete pour — required for detached ADUs with new foundations

  2. 2

    Framing

    Structural framing complete, before insulation or wall cover

  3. 3

    MEP Rough-In

    Mechanical, electrical, and plumbing rough-in before walls closed; separate trade permits required

  4. 4

    Final

    All work complete per approved plans, ready for occupancy

See the full Unincorporated Natrona County inspection guide — scheduling & re-inspection fees →

Tips

  • ADU eligibility is zoning-district-specific and acreage-dependent in the county's agricultural/mountain districts (UA, MR-1: 1 per 10 acres; MR-2: 1 per 5 acres) versus flat 1-per-lot in SR/RR, and 2-acre minimum lot size in UR — confirm your district and lot size with Natrona County Planning (via the Planning & Zoning page) BEFORE designing your ADU.
  • Owner-occupancy of the PRIMARY dwelling is mandatory under § 4.11.05(A)(7) — you cannot rent out the main house and live in the ADU, or own the property as a pure rental with neither unit owner-occupied. Owner-builder
  • Size cap is the SMALLER of 50% of the primary dwelling's square footage or 1,000 gross sq ft habitable — calculate both figures for your specific primary home.
  • ADUs cannot be sold separately from the primary residence — they remain a single conveyable property.

Frequently asked questions

Unincorporated Natrona County requires an accessory dwelling unit (adu) permit for: Zoning eligibility: ADU must be an accessory use to a legally permitted single-unit residential use in a district where ADUs are listed as Permitted (Table 4.02, districts include UA, MR-1, MR-2, SR, RR, UR) — confirm with Natrona County Planning Department before applying for the building permit; Number: One (1) ADU permitted per lot as accessory to a legally permitted single-unit residential use; in the UR district, the lot must be a minimum of 2 acres; Density in agricultural/mountain districts is expressed per-acre: e.g. UA and MR-1 allow 1 ADU per 10 acres (1 exempt ADU for agricultural-tax-status properties per 10 acres); MR-2 allows 1 ADU per 5 acres; SR and RR allow 1 ADU per lot; Setbacks: a detached ADU must comply with the zoning district's required (principal or accessory, as applicable) setbacks; an attached ADU must comply with principal building setbacks for its district; Height: an ADU must NOT exceed the height of the primary dwelling; Size: an ADU must not exceed 50% of the primary dwelling's square footage OR 1,000 gross square feet of habitable floor area, whichever is SMALLER; Occupancy: the property owner (title holder or contract purchaser) must occupy the principal dwelling as their permanent residence — owner-occupancy of the primary unit is mandatory; Use restriction: ADUs may not be sold separately from the primary residence, and must maintain architectural consistency with the primary dwelling; Once zoning compliance is confirmed, the ADU is built under the standard Natrona County Building Permit Application (select New Construction or Addition, per whether attached or detached) — plus separate Electrical, Plumbing, and Mechanical permits as applicable. If your project isn't listed, confirm with Natrona County Building Department at (307) 235-9435 before starting work.

In Unincorporated Natrona County, the published Building Permit Fee — valuation-based (same table as new construction) is: $70 (valuation $0–$2,500) up to $905 plus $9.24 per additional $1,000 over $98,000. These are the jurisdiction's own published figures — see the fee schedule table and source citations on this page.

Plan review for an accessory dwelling unit (adu) permit in Unincorporated Natrona County typically runs 5–15 business days. This is an estimate, not a published figure — confirm current review times with Natrona County Building Department at (307) 235-9435.

You'll need: Natrona County Building Permit Application (2025); Site Plan Application (2025). Depending on your project, Unincorporated Natrona County may also ask for: Natrona Next Zoning Resolution — § 4.11.05(A). See the required-documents checklist on this page for details on each.

Apply through Natrona County Building Department at 200 N. Center St, Room 205, Casper, WY 82601. Phone: (307) 235-9435, email: Contact via natronacounty-wy.gov (email obfuscated on site; call 307-235-9435). Office hours: Monday–Friday, 8:00 AM–5:00 PM. Official information: https://www.natronacounty-wy.gov/170/Building-Inspection.

Yes, if your property is in a zoning district where ADUs are a Permitted use (UA, MR-1, MR-2, SR, RR, and UR per Zoning Resolution Table 4.02) and you occupy the primary dwelling as your permanent residence. Density limits apply in agricultural/mountain districts (e.g., 1 ADU per 10 acres in UA/MR-1). Confirm eligibility with Natrona County Planning, then apply for a standard Building Permit.

An ADU may not exceed 50% of the primary dwelling's square footage or 1,000 gross square feet of habitable floor area, whichever is smaller, and its height cannot exceed the primary dwelling's height (Zoning Resolution § 4.11.05(A)(5)-(6)).

Yes. Per § 4.11.05(A)(7), the property owner must occupy the principal dwelling as their permanent residence for an ADU to be permitted on the lot.

Sources & verification

Verified against official sources. Last reviewed 2026-07-01.

Fees, timelines, and adopted codes are researched from each jurisdiction's published records — see how we verify. Requirements change and vary by project, so always confirm the current details with the Unincorporated Natrona County building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.

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Accessory Dwelling Unit (ADU) Permit in other cities

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