Does Rock Springs allow accessory dwelling units (ADUs)?

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.

How big can an ADU be in Rock Springs?

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)).

Can I rent out both the main house and the ADU to different tenants in Rock Springs?

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

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

Verified

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

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 publishedBuilding permit fee for a newly constructed accessory dwelling

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))
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

Req
Building Permit Application
Standard City of Rock Springs Building Permit Application, required for ADU construction after zoning confirmation
Req
Site Plan
Showing the principal dwelling, proposed accessory dwelling location, required off-street parking space, and setbacks

Fee schedule

Fee type	Amount	Notes
Building permit fee for a newly constructed accessory dwelling	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	§ 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

Review timeline

~10–30 business days

Typical estimate — confirm current times with the Rock Springs building department

Inspection process

1
Foundation
Accessory dwellings must be on a permanent foundation per the § 157.008 definition; footings below 42-inch frost depth
2
Framing
Structural framing, matching roof pitch/siding/finish to the principal dwelling
3
MEP Rough-In
Mechanical, electrical (City Electrical Inspector), plumbing rough-in
4
Final
All work complete, ready for occupancy

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.
Manufactured/mobile homes, RVs, campers, and similar cannot be used as an ADU under § 157.086(B)(13)(g).

Frequently asked questions

Does Rock Springs allow accessory dwelling units (ADUs)?: 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.
How big can an ADU be in Rock Springs?: 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)).
Can I rent out both the main house and the ADU to different tenants in Rock Springs?: 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.

Other permits in Rock Springs

Residential Building Permit (New Construction)Residential Addition / Remodel Permit Electrical Permit Plumbing Permit Mechanical / HVAC Permit Roofing Permit (Reroof)Solar PV Permit Demolition Permit Commercial Tenant Improvement Permit

Related guides

ADU / In-Law Suite

Get the AI compliance checklist

Upload your project scope, get a jurisdiction-specific checklist of everything you need. Coming soon.

We only use your email to send permit updates. No spam, unsubscribe anytime. Privacy.