Can I Build an ADU (Accessory Dwelling Unit) in Wyoming?
Quick Answer
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.
Bottom Line
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.