In plain words

Wyoming has no state law that makes towns allow ADUs. An ADU (accessory dwelling unit) is a second, smaller home on the same lot as a house. Each city, town and county decides through its own zoning. Zoning means the local rules about what can be built where. Cities zone the land inside city limits. Counties may zone the land outside towns, and some rural areas have few zoning rules. So the answer depends on exactly where your lot sits. Local rules differ a lot. Cheyenne allows one ADU on a single-home lot after a staff review. It can be up to 40% of the house or 1,200 square feet, whichever is less. In February 2026 it dropped its owner-occupancy rule, which had required the owner to live on the property. Casper is reported to allow ADUs in only one zone, and only after a public hearing. Rural lots in Laramie County need at least 10.5 acres for an ADU. One state law helps with timing. Since July 1, 2026, the Fast Track Permits Act sets deadlines for home building permits. Local offices get 10 business days to say whether an application is complete. They then have 30 days to approve or deny it, unless the clock is paused. If they miss the deadline, the permit counts as approved, but the building must still pass inspections. It covers buildings with one or two homes, up to three stories. It applies only where the local government uses the International Residential Code, a standard building code many places adopt. It does not change zoning, so it cannot make an ADU legal where local rules ban it. A 2024 plan to allow ADUs statewide never became a bill. You still need local approval, and your lot must work for an ADU.

The rules at a glance

State ADU lawNo. Each city, town or county decides.
Owner living on siteTowns may require the owner to live on the property.
ParkingState law doesn’t set this. Local rules vary: Cheyenne requires one extra off-street space for an ADU (with more ways to meet it after a 2026 change), and Casper is reported to require two spaces per unit.
SizeState law doesn’t set this. Local caps vary: Cheyenne allows up to 40% of the main home or 1,200 sq ft, whichever is less (basement apartments can use the whole basement); unincorporated Laramie County caps ADUs at half the main home in urban zones and allows up to the same size on rural lots; Casper is reported to cap detached ADUs at 1,500 sq ft or 15% of the lot.
Lot size and setbacksState law doesn’t set this. Cities, towns and counties set lot size, setback and placement rules; for example, unincorporated Laramie County requires at least 10.5 acres for an ADU in its rural residential zones.
FeesState law doesn’t set this. Permit, tap and utility fees are set locally. Under the 2026 Fast Track Permits Act, conditions added to a residential building permit after approval trigger a 10% cut in the permit fee unless unexpected site conditions require them.
Short-term rentalsState law doesn’t set this. Short-term rental rules, where they exist, are set by each city, town or county.

What to do next

  1. Find out whether your lot is inside city or town limits or in unincorporated county land, and call that planning office.
  2. Ask whether ADUs are allowed in your zone and what approval is needed: a staff review, or a conditional use permit with a public hearing.
  3. Get the local size cap, parking, owner-occupancy and design rules in writing before you pay for plans.
  4. On rural lots, check septic (county environmental health) and well permits (State Engineer's Office) before designing.
  5. When you file the building permit, note the date: under the 2026 Fast Track Permits Act the office owes you a completeness notice within 10 business days and a decision within 30 days after that, unless paused.
  6. Read your deed and any HOA covenants; private restrictions can block an ADU even where zoning allows one.

What your town still decides

Wyoming leaves ADU decisions entirely to local governments. Cities and towns zone land inside their limits under W.S. 15-1-601, and boards of county commissioners may zone unincorporated land under W.S. 18-5-201. Some counties zone only lightly, so on rural land the main hurdles are often septic permits from county environmental health and well permits from the State Engineer's Office. Where ADUs are allowed, the approval path ranges from a staff-level administrative review (Cheyenne) to a conditional use permit with a public hearing (Casper). The only statewide law touching ADU projects is the 2026 Fast Track Permits Act, which speeds residential building permits but leaves zoning alone. A 2024 interim draft that would have required towns to allow accessory units never became a bill, and no ADU bill appears in the 2023 through 2026 sessions or among the committee drafts approved for the 2027 session as of this check.

Examples of local rules

  • Cheyenne: ADUs are allowed through administrative (staff) approval in any zone that allows single-family homes: one per detached single-family lot, up to 40% of the main home or 1,200 sq ft, whichever is less, with design that matches the house. The ADU can be inside the house, in an accessory building, or a flat-over-flat unit. On February 9, 2026 the City Council removed the owner-occupancy requirement and loosened how the extra parking space can be provided. Source
  • Laramie County (unincorporated, around Cheyenne): ADUs are allowed in urban residential zones served by central water and sewer, capped at half the size of the main home. In rural residential zones they can be as large as the main home but need a lot of at least 10.5 acres, a septic permit and well approvals. The main home must exist first, and a building permit is required. Source
  • Casper: Reported to allow ADUs only in the R-2 zone and only with a conditional use permit after a Planning and Zoning Commission hearing (Casper Municipal Code 17.32.030(J)). Detached ADUs are reported to be capped at 1,500 sq ft or 15% of the lot, the owner or immediate family must live in one unit, and two parking spaces per unit apply. These details come from a secondary summary and were not checked against the code itself. Source

What we’re still confirming

  • Whether the state's Fast Track Permits Act deadlines cover every ADU, such as an apartment in a garage, hasn't been tested.

Laws, bills and citations

The laws behind this (1)
  • Fast Track Permits Act (building permit deadlines; not an ADU zoning law) (2026 Wyo. Sess. Laws ch. 42 (HB0002, Enrolled Act No. 16, 2026 Budget Session); W.S. 16-13-101 and 16-13-102, signed March 5, 2026, in effect July 1, 2026). Sets deadlines for residential building permits in cities and counties that have adopted the International Residential Code. The local office must say within 10 business days whether an application is complete, then approve or deny within 30 days, or the permit is deemed approved. It covers buildings with one or two homes, up to three stories and 3,000 sq ft per home, which appears to include most ADU building permits, but it does not change zoning or make ADUs legal anywhere. Read it
Proposed and failed bills (2). None of these is law.
  • 24LSO-0280 draft, 'Accessory residential units-permits' (2024 Budget Session): died as of October 3, 2026. A working draft from the housing subcommittee of a Regulatory Reform Task Force set up under the Legislature's Management Council. It would have let lot owners add an accessory home up to 75% of the size of the existing house and barred towns from requiring extra parking, street improvements or other conditions. The subcommittee voted 8-4 in November 2023 to send it on to a legislative committee, but it was never introduced: no 2024, 2025 or 2026 bill uses the phrase 'accessory dwelling' or 'accessory residential' in its text. Bill page
  • HB0202 (2025): died as of October 3, 2026. The first version of the Fast Track Permits Act. It would have set deadlines (15 days to say an application is complete, 60 days to decide) for local review of building permits and other land-use requests for uses already allowed by zoning. It passed the House but died in the Senate Minerals Committee on March 3, 2025. A narrower bill limited to residential building permits, HB0002, became law in 2026. Bill page

Sources

  1. 2026 Wyo. Sess. Laws ch. 42 (HB0002, Enrolled Act No. 16, 2026 Budget Session); W.S. 16-13-101 and 16-13-102 · official source
  2. Wyoming Legislature: HB0002 (2026) bill digest and history (Governor signed 3/5/2026; Chapter 42) · official source · checked 2026-10-03
  3. Wyoming Legislature: HB0202 (2025) bill digest and history (died in Senate Minerals Committee 3/3/2025) · official source · checked 2026-10-03
  4. Wyoming Legislature: 2026 Budget Session bill list (HB0002 chapter 42; SF0042, SF0064 and other housing bills failed) · official source · checked 2026-10-03
  5. Wyoming Legislature: 2025 General Session bill list (HB0202 died; no ADU bill) · official source · checked 2026-10-03
  6. Wyoming Legislature: 2024 Budget Session bill list (no ADU bill introduced) · official source · checked 2026-10-03
  7. Wyoming Legislature: 2023 General Session bill list (no ADU bill) · official source · checked 2026-10-03
  8. Wyoming Legislature: Committee bills approved for the 2027 General Session (no ADU draft) · official source · checked 2026-10-03
  9. Wyoming Legislature: SF0042 (2026) introduced text, quoting current W.S. 18-5-201 county zoning authority · official source · checked 2026-10-03
  10. City of Cheyenne Planning Commission staff report PLTA-25-10 (January 5, 2026), UDC 5.7.3 Accessory Dwelling Units · official source · checked 2026-10-03
  11. Laramie County Planning: Accessory Dwelling Unit Guide · official source · checked 2026-10-03
  12. Cap City News: Cheyenne removes owner-occupancy rules for accessory dwelling units (February 10, 2026) · checked 2026-10-03
  13. Cap City News: Judge blocks Montana law curbing local control, sister to Wyoming bill (January 31, 2024) · checked 2026-10-03
  14. ADU Rulebook: Casper, WY ADU rules (reviewed August 2026) · checked 2026-10-03

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.