Can I Build an ADU (Accessory Dwelling Unit) in Wyoming?
ADU permit requirements. State law, internal vs. detached, basement apartments, and impact fee waivers.
Often yes — many states now require cities to allow at least internal ADUs.
Wyoming-specific rules
Wyoming has no statewide building code. Under W.S. § 35-9-121, local building-code enforcement is opt-in: a city or county must apply to the State Fire Marshal for authority and adopt standards at least as stringent as the state's — otherwise no local building code applies, and many unincorporated county areas require no building permit at all. Confirm whether your specific jurisdiction has adopted and enforces a building code before relying on any permit requirement.
Sources: Wyoming State Fire Marshal — building-code enforcement (W.S. § 35-9-106 / 121)
State Law May Require It
A growing number of states have passed laws requiring cities to allow at least internal ADUs (within the existing footprint of the home — basement apartments, above-garage units, etc.). Many cities also allow detached ADUs, though rules on size and placement vary. Check whether your state has an ADU-enabling law before assuming your city can simply say no.
Types of ADUs
Internal ADUs include basement apartments, converted attic space, and attached additions. Detached ADUs include backyard cottages, converted garages, and purpose-built accessory structures. Each type has different permit requirements and setback rules.
Key Requirements
Most ADUs need: a separate entrance from the primary dwelling, adequate parking (usually one additional off-street space), fire separation (1-hour rating for internal ADUs), and compliance with all building codes for habitable space. Basement ADUs require egress windows in every bedroom.
Reduced Impact Fees
Some states limit impact fees for ADUs, making them cheaper to permit than a full second dwelling. Many cities waive or significantly reduce impact fees for ADUs. Ask your city about current fee schedules — this can save thousands of dollars.
In many states you can build an ADU thanks to state law requiring cities to allow it. Internal ADUs are the easiest path. Start by checking your state's ADU law and your city's specific ADU ordinance.
Permit fees by city in Wyoming
Verified from each city’s published fee schedule. Where a city has no separate fee listed for this project, open the city page for the current requirements and amount.
| City | Permit fee | Source |
|---|---|---|
| Casper | $35Verified | Accessory Dwelling Unit (ADU) Permit → |
| Cheyenne | $600.00Verified | Accessory Dwelling Unit (ADU) Permit → |
| Evanston | $0.010 × project cost (minimum charge $30.00)Verified | Accessory Dwelling Unit (ADU) Permit → |
| Gillette | $30–$150+$0.04/sq ft — same Building Square Feet table as new constructionVerified | Accessory Dwelling Unit (ADU) Permit → |
| Green River | See city page for the current Accessory Dwelling Unit (ADU) Permit fee | Accessory Dwelling Unit (ADU) Permit → |
| Jackson | $1.70/sq ft (new construction) or valuation-based (addition to existing home)Verified | Accessory Residential Unit (ARU) Permit → |
| Laramie | Per the general Building Permit and Plan Review Fee Schedule — e.g., $23.50 for $1–$500 valuation, scaling per the tableVerified | Accessory Dwelling Unit (ADU) Permit → |
| Riverton | $0.42 per square foot of building area (includes building and all building systems)Verified | Accessory Dwelling Unit (ADU) Permit → |
| Rock Springs | Charged under the general § 150.08(B) valuation-based fee schedule (new detached structure) or the 50% residential-alteration rate if converting existing accessory space — no ADU-specific fee line is publishedVerified | Accessory Dwelling Unit (ADU) Permit → |
| Sheridan | Valuation x 0.03 x 0.8Verified | Accessory Dwelling Unit (ADU) Permit → |
| Unincorporated Albany County | $300.00Verifiedvia Zoning Certificate & Rural Address (county's "Building Permit" stand-in) | Zoning Certificate & Rural Address (county's "Building Permit" stand-in) → |
| Unincorporated Campbell County | No feeVerified | Accessory Dwelling Unit (ADU) Permit → |
| Unincorporated Laramie County | Varies by project valuation — see Laramie County 2022 Building and Plan Review Fee ScheduleVerified | Accessory Dwelling Unit (ADU) Permit → |
| Unincorporated Natrona County | $70 (valuation $0–$2,500) up to $905 plus $9.24 per additional $1,000 over $98,000Verified | Accessory Dwelling Unit (ADU) Permit → |
| Unincorporated Sheridan County | $150.00Verifiedvia Zoning Permit | Zoning Permit → |
| Unincorporated Sweetwater County | $50.00Verifiedvia Zoning/Construction Permit (Land Use) — not a building-code permit | Zoning/Construction Permit (Land Use) — not a building-code permit → |
| Unincorporated Teton County | No separate ARU permit fee; charged under the standard valuation-based Residential Building Permit fee schedule (ARU floor area included in total valuation)Verified | Accessory Residential Unit (ARU) → |
| Unincorporated Uinta County | $50.00Verifiedvia Land Use Certificate (Zoning / Use Approval) | Land Use Certificate (Zoning / Use Approval) → |