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Accessory Dwelling Unit (ADU) Permit in Rock Springs, Wyoming

Rock Springs' Zoning Ordinance (Rock Springs Municipal Code Chapter 157) explicitly permits ACCESSORY DWELLINGS as a use in the R-2 Low Density Residential Zone (§ 157.086(A)(2)), with detailed development standards at § 157.086(B)(13). An accessory dwelling requires BOTH a zoning determination (that the property is properly zoned R-2, or another zone where the use is separately listed in the Table of Uses) and a standard residential building permit for construction.

Verified 2026-07-01 · Source

When you need this permit

  • Zone eligibility: the R-2 Low Density Residential Zone is purpose-built to allow 'single-family detached dwellings, accessory dwelling units and directly related complementary uses' (§ 157.086(A)(2)); verify zoning of the specific parcel via the Table of Uses in § 157.086(B) or by contacting the Planning Office (307-352-1540)
  • Definition: an ACCESSORY DWELLING is 'a detached structure which is accessory to a single-family dwelling, located on the same lot as a single-family dwelling and placed on a permanent foundation, with no more than one bedroom and provides basic requirements for living, sleeping and sanitation' (§ 157.008)
  • General accessory-building rules apply (§ 157.129): not located in a front yard; not in a utility easement; combined accessory floor area over 1,500 sq ft requires a conditional use permit
  • Size: newly constructed or newly converted accessory dwelling square footage shall be no more than 75% of the principal building's square footage OR 800 sq ft, whichever is less; in no case less than 300 sq ft (§ 157.086(B)(13)(b))
  • Design: any newly constructed accessory dwelling must have roof pitch, siding, and exterior finish matching the principal building in style and material (existing pre-ordinance structures are exempt) (§ 157.086(B)(13)(c))
  • Parking: at least one off-street parking space dedicated solely to the accessory dwelling occupants, in addition to the principal building's required parking; this space may be inside the accessory dwelling structure if the remaining non-parking area is at least 300 sq ft (§ 157.086(B)(13)(d))
  • Owner occupancy: either the principal building or the accessory dwelling must be owner-occupied (§ 157.086(B)(13)(e)) Owner-builder
  • Number: a maximum of ONE accessory dwelling is allowed per parcel or lot (§ 157.086(B)(13)(f))
  • Prohibited: mobile homes, recreational vehicles, motor vehicles, boats, and similar are NOT considered accessory dwellings (§ 157.086(B)(13)(g))
  • Once zoning eligibility and standards are confirmed, construction requires the standard Building Permit Application and is subject to the 2024 IRC/IBC and the general valuation-based fee schedule (or residential-alteration 50% rate if converting existing space)

Required documents

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Fee schedule

Building permit fee for a newly constructed accessory dwelling§ 150.08(A)/(B)(3); the fee mechanism depends on whether the ADU is new construction or a conversion, per the general building-fee rules
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 published

Review timeline

Plan reviewTypical estimate — confirm current times with the Rock Springs building department
~10–30 business days

How long did your Accessory Dwelling Unit (ADU) Permit permit actually take in Rock Springs?

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

Inspection process

  1. 1

    Foundation

    Accessory dwellings must be on a permanent foundation per the § 157.008 definition; footings below 42-inch frost depth

  2. 2

    Framing

    Structural framing, matching roof pitch/siding/finish to the principal dwelling

  3. 3

    MEP Rough-In

    Mechanical, electrical (City Electrical Inspector), plumbing rough-in

  4. 4

    Final

    All work complete, ready for occupancy

See the full Rock Springs inspection guide — scheduling & re-inspection fees →

Tips

  • Rock Springs' ADU standard is genuinely grounded in the zoning ordinance text (§ 157.086(B)(13)), not inferred — it is one of the more detailed ADU standards among Wyoming cities researched, with explicit size, design, parking, owner-occupancy, and one-per-lot rules.
  • The R-2 zone is the zone purpose-built for ADUs; confirm your parcel's actual zoning designation with the Planning Office before assuming ADU eligibility, since the use may not be listed for every residential zone.
  • Maximum ADU size is capped at the LESSER of 75% of the principal dwelling's square footage or 800 sq ft — a large principal home does not automatically unlock a large ADU.
  • Either the main house or the ADU must be owner-occupied — pure investor rental of both units is not permitted. Owner-builder
  • Manufactured/mobile homes, RVs, campers, and similar cannot be used as an ADU under § 157.086(B)(13)(g).

Frequently asked questions

Rock Springs requires an accessory dwelling unit (adu) permit for: Zone eligibility: the R-2 Low Density Residential Zone is purpose-built to allow 'single-family detached dwellings, accessory dwelling units and directly related complementary uses' (§ 157.086(A)(2)); verify zoning of the specific parcel via the Table of Uses in § 157.086(B) or by contacting the Planning Office (307-352-1540); Definition: an ACCESSORY DWELLING is 'a detached structure which is accessory to a single-family dwelling, located on the same lot as a single-family dwelling and placed on a permanent foundation, with no more than one bedroom and provides basic requirements for living, sleeping and sanitation' (§ 157.008); General accessory-building rules apply (§ 157.129): not located in a front yard; not in a utility easement; combined accessory floor area over 1,500 sq ft requires a conditional use permit; Size: newly constructed or newly converted accessory dwelling square footage shall be no more than 75% of the principal building's square footage OR 800 sq ft, whichever is less; in no case less than 300 sq ft (§ 157.086(B)(13)(b)); Design: any newly constructed accessory dwelling must have roof pitch, siding, and exterior finish matching the principal building in style and material (existing pre-ordinance structures are exempt) (§ 157.086(B)(13)(c)); Parking: at least one off-street parking space dedicated solely to the accessory dwelling occupants, in addition to the principal building's required parking; this space may be inside the accessory dwelling structure if the remaining non-parking area is at least 300 sq ft (§ 157.086(B)(13)(d)); Owner occupancy: either the principal building or the accessory dwelling must be owner-occupied (§ 157.086(B)(13)(e)); Number: a maximum of ONE accessory dwelling is allowed per parcel or lot (§ 157.086(B)(13)(f)); Prohibited: mobile homes, recreational vehicles, motor vehicles, boats, and similar are NOT considered accessory dwellings (§ 157.086(B)(13)(g)); Once zoning eligibility and standards are confirmed, construction requires the standard Building Permit Application and is subject to the 2024 IRC/IBC and the general valuation-based fee schedule (or residential-alteration 50% rate if converting existing space). If your project isn't listed, confirm with City of Rock Springs Public Services Department — Building Inspections & Permits (Chief Building Inspector) at (307) 352-1540 before starting work.

In Rock Springs, the published Building permit fee for a newly constructed accessory dwelling is: 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 published. 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 Rock Springs typically runs 10–30 business days. This is an estimate, not a published figure — confirm current review times with City of Rock Springs Public Services Department — Building Inspections & Permits (Chief Building Inspector) at (307) 352-1540.

You'll need: Building Permit Application; Site Plan. See the required-documents checklist on this page for details on each.

Apply through City of Rock Springs Public Services Department — Building Inspections & Permits (Chief Building Inspector) at 212 D Street, Rock Springs, WY 82901. Phone: (307) 352-1540, email: webmaster@rswy.net. Office hours: Mon–Fri, 8:00 a.m. to 5:00 p.m., closed 12:30–1:30 p.m. for lunch. Official information: https://www.rswy.net/departments/public_services/building_inspections_permits.php.

Yes. The R-2 Low Density Residential Zone explicitly permits accessory dwelling units (§ 157.086(A)(2)), with detailed standards in § 157.086(B)(13): max size is the lesser of 75% of the principal building or 800 sq ft (min. 300 sq ft), matching exterior design, one dedicated parking space, owner-occupancy of either unit, and a maximum of one ADU per lot.

No more than 75% of the principal building's square footage, or 800 square feet, whichever is less. The minimum size is 300 square feet (§ 157.086(B)(13)(b)).

No — either the principal building or the accessory dwelling must be owner-occupied per § 157.086(B)(13)(e).

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 Rock Springs 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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