How big can an ADU be in unincorporated Laramie County?

Per the county's Accessory Dwelling Unit Guide and Guidance for Residential Projects handout, an ADU may not exceed 50% of the floor area of the principal dwelling, with an absolute maximum of 1,200 square feet (and, per the 2024 IRC Appendix BC construction standard the county applies, a minimum of 190 square feet). In the LU and RRH rural zoning districts, an ADU may be up to the same size as the principal dwelling.

Do I need to own and live on the property to build an ADU in unincorporated Laramie County?

The property must already have a principal dwelling built on it before an ADU application is accepted, and per the county's cited 2024 IRC Appendix BC standard, the owner must reside in either the primary dwelling unit or the ADU as of the date of permit approval.

What is the minimum lot size for an ADU in a rural part of unincorporated Laramie County?

In the LU (rural) and RRH zoning districts, an ADU requires a minimum lot size of 10.5 acres, per Laramie County Land Use Regulations Section 3-1-107 Part E.

Accessory Dwelling Unit (ADU) Permit in Unincorporated Laramie County, Wyoming

Verified

Required for construction of an ADU in unincorporated Laramie County. Zoning eligibility and dimensional/utility standards are set by Laramie County Land Use Regulations Section 3-1-107 Part E; construction standards follow 2024 IRC Appendix BC (Accessory Dwelling Units), which the county distributes as its official ADU building-code handout. A separate Non-Traditional Housing Approval Permit from Planning and Zoning is required in addition to the building permit.

Verified 2026-07-01 · Source

Varies by project valuation — see Laramie County 2022 Building and Plan Review Fee ScheduleBuilding Permit Fee — same valuation-based table as new construction

When you need this permit

Zoning: ADU is allowed in all urbanized residential zoning districts (URLD, URMD, URHD, MU, PUD) with central water and sewer, and in rural residential districts (RRH/LU) with a minimum lot size of 10.5 acres
Size: no larger than 50% of the floor area of the principal dwelling in URLD/URMD/URHD/MU/PUD districts; may be up to the same size as the principal dwelling in LU and RRH districts; per the Guidance for Residential Projects handout, allowable square footage is 50% of the primary dwelling up to a maximum of 1,200 square feet
A principal dwelling must be built on the lot BEFORE an application for an ADU is submitted
ADU must be situated on the same lot as the principal dwelling and must meet setback, parking, and maximum lot-coverage requirements
In URLD/URMD/URHD/MU districts, ADU must connect to South Cheyenne Water & Sewer District for water/sewer service
In RRH/LU districts, ADU requires a septic permit from Laramie County Environmental Health and any necessary well approvals from the Wyoming State Engineer's Office; prior approval from South Cheyenne Water & Sewer District or Environmental Health is required BEFORE a building permit is issued
Under 2024 IRC Appendix BC (the county's cited ADU construction standard): ADU permitted only within an existing single-family detached dwelling or existing townhouse unit within IRC scope; only one ADU per primary dwelling unit; owner must reside in either the primary dwelling or the ADU as of permit approval; ADU must have a separate house number; ADU must be not less than 190 sq ft and not more than 50% of the primary dwelling's area, capped at 1,200 sq ft; ADU must have a separate entrance from the primary dwelling; maximum of two bedrooms; separate heating system, ducting, and climate controls required (BC105.1); ready access to service disconnects and overcurrent devices required (BC105.2); ready access to gas shutoff valves required (BC105.3); water service may be shared with separate accessible shutoffs (BC105.4)
A Non-Traditional Housing Approval Permit (Planning and Zoning application) is required in addition to the building permit application
IRC Letter required for modular-home ADUs stating the code the unit was built to

Required documents

Req
Non-Traditional Housing Approval Permit Application (Planning and Zoning)
Required zoning-side approval before/alongside the building permit application
Req
Building Permit Application (SmartGov portal)
Standard residential building permit application for the ADU structure
Req
Plot Plan
Minimum requirements
Req
Building Plans
Clear set of plans with all rooms labeled, all room dimensions, outside overall dimensions, and underslab utility/mechanical room locations
Opt
IRC Letter for Modular Homes
States the building code and electrical code the unit was built to
Opt
Accessory Dwelling Unit Guide (county handout)
County's plain-language ADU guide summarizing LCLUR § 3-1-107 Part E standards

Fee schedule

Fee type	Amount	Notes
Building Permit Fee — same valuation-based table as new construction	Varies by project valuation — see Laramie County 2022 Building and Plan Review Fee Schedule	Laramie County Building Permit Fee Schedule (PDF); the Guidance for Residential Projects treats an ADU as a standard valuation-based residential permit
Plan Review Fee	65% of the Building Permit Fee	—

Review timeline

7–10 business days

Unincorporated Laramie County’s published plan-review target

Inspection process

1
Foundation
Before concrete pour
2
Rough Framing / Rough MEP
Framing, mechanical, electrical, plumbing rough-in before covering
3
Final
Required before occupancy

Tips

Contact Laramie County Planning (307-633-4303 / planning@laramiecountywy.gov) FIRST, before applying for a building permit — the Non-Traditional Housing zoning approval must be secured, and in RRH/LU districts, Environmental Health or the South Cheyenne Water & Sewer District must approve septic/sewer capacity BEFORE a building permit is issued.
In rural (RRH/LU) zoning districts, an ADU requires a minimum 10.5-acre lot — this is a much larger minimum lot size than in the urbanized residential districts, where public water/sewer service is instead the qualifying condition.
The county's max-size figure (50% of primary dwelling, capped at 1,200 sq ft) as stated in the Guidance for Residential Projects handout is consistent with, but numerically distinct from, the IRC Appendix BC construction-code cap (50% of primary dwelling, capped at 1,200 sq ft, with a 190 sq ft floor) — both apply; the more restrictive number in a given case controls.

Frequently asked questions

How big can an ADU be in unincorporated Laramie County?: Per the county's Accessory Dwelling Unit Guide and Guidance for Residential Projects handout, an ADU may not exceed 50% of the floor area of the principal dwelling, with an absolute maximum of 1,200 square feet (and, per the 2024 IRC Appendix BC construction standard the county applies, a minimum of 190 square feet). In the LU and RRH rural zoning districts, an ADU may be up to the same size as the principal dwelling.
Do I need to own and live on the property to build an ADU in unincorporated Laramie County?: The property must already have a principal dwelling built on it before an ADU application is accepted, and per the county's cited 2024 IRC Appendix BC standard, the owner must reside in either the primary dwelling unit or the ADU as of the date of permit approval.
What is the minimum lot size for an ADU in a rural part of unincorporated Laramie County?: In the LU (rural) and RRH zoning districts, an ADU requires a minimum lot size of 10.5 acres, per Laramie County Land Use Regulations Section 3-1-107 Part 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 Unincorporated Laramie County building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.

Other permits in Unincorporated Laramie County

Residential Building Permit (New Single-Family Residence)Residential Addition, Remodel, Deck/Patio/Porch, and Basement Finish Permit Electrical Permit Plumbing Permit Mechanical / HVAC Permit Roofing Permit Solar PV Permit Demolition Permit Commercial Tenant Improvement / Renovation Permit

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