Building permits, zoning and land rules in Adams County, Colorado

Unincorporated Adams County requires a building permit before construction, enlargement, alteration, repair, moving, demolition, occupancy changes, and listed electrical, gas, mechanical, plumbing, and sign work¹. Listed exemptions include decks no more than 30 inches above grade, storage sheds and gazebos no larger than 200 square feet, landscaping, and painting; larger accessory buildings and sheds require building permits¹. Permitted construction receives inspections based on the approved plans, and applicants must schedule inspections at least 48 hours ahead¹⁰. An owner may apply for a building permit on the owner's property, but required building permits and proof of compliance still apply; contractors must register before pulling a building permit⁸. We could not confirm a general agricultural-building exemption; ask the Building Safety Division before relying on one¹.

Adams County's Building Safety Division handles building permits and inspections for unincorporated land; call 720.523.6800¹. Thornton handles its own building permits, as do Arvada and Westminster, cities that reach into Adams County^11,12,13. Septic permits for Adams County properties remain with the Adams County Health Department⁴. Submit county building applications and project-specific documents through the E-Permit Center; the county accepts payment only through that portal^1,10. Adams County uses the 2024 International Codes for applications received on or after July 1, 2026; complete applications accepted earlier use the 2018 editions¹⁴. Building-permit fees depend on labor-and-material valuation, with residential plan review costing 65% of the permit fee when submittal documents are required^1,15. Adams County requires a certificate of occupancy before a business operates and issues certificates for new construction or major renovations; that requirement does not establish a certificate requirement for every residential repair¹⁰. For applicable residential/ADU projects, contact the E-Permit Center after passing the final building inspection; required inspections and applicable health, stormwater and infrastructure sign-offs must be complete¹⁶.

Adams County requires prior authorization for land use and development in unincorporated areas; underlying and overlay zoning districts determine permitted uses and development standards, with boundaries shown on county zoning maps^17,18. Thornton, Commerce City, Federal Heights and Bennett set their own zoning^19,20,21,22. Aurora, Arvada, Westminster and Lochbuie, which reach into Adams County, also set their own zoning; septic permits for properties in Adams County stay with the Adams County Health Department^{4,23,24,25,26}. County minimum lot sizes and setbacks vary by district^9,18. For Agricultural-1 accessory structures, a county variance case identifies a 100-foot front-property-line setback, while the district standards require 120 feet from a section line, subject to a Public Works exception; these are different measurements^18,27. Published lot-coverage percentages apply only to attached single-family dwellings²⁸. Confirm the parcel's district, overlays and dimensions with Community & Economic Development before designing⁵.

The Adams County Health Department's Water Quality Program issues septic, or onsite wastewater treatment system (OWTS), permits countywide⁴. Installation, expansion and substantive repairs need a septic permit under Regulation O-26⁴. For a new septic connection, obtain a soils report and design from a designer who has passed the NAWT design course; some projects require a Colorado-registered professional engineer, and replacing only a tank does not require a full design⁴. Submit the application, design and soils report by email, online portal or in person, and pay the applicable fee⁴. Replacing risers, lids or distribution boxes needs no septic permit when the work does not add, repair, replace, expand, mitigate or abandon a septic tank, leach field, sewer line or effluent line⁴. Use a county-licensed installer, who requests final inspection; obtain approval before backfilling, then the designer's compliance letter and the septic use permit needed for house occupancy certification⁴. Most sales or title transfers require a use/transfer septic permit and an NAWT- or NSF-certified inspection, usually including tank pumping⁴. About 57.1% of county soils are rated as not severely limited for a conventional drain field; evaluate the actual site²⁹.

Unincorporated Adams County limits RV occupancy to one stay of no more than 30 consecutive days per calendar year, in conjunction with a residence; parking, storage and setback rules also apply⁶. Tiny-home villages require a conditional-use permit and must provide housing for people experiencing or at risk of homelessness, or transitional housing; the minimum site is 0.5 acre with at least 10 homes²⁸. Village homes must be 100–400 square feet, excluding lofts from the maximum, on qualifying foundations and built to the county's adopted IRC²⁸. Village standards do not establish permission for a standalone tiny home; ask Community & Economic Development about the proposed use⁵. County dwelling minimums include 1,800 square feet in Residential Estate, 1,250 in Residential-1-C and for Residential-2 single-family homes, and 600 in Mobile Home Dwelling¹⁸. Residential-3 minimums are 450 square feet for an efficiency unit, then 600, 750, 900 and 1,000 for one-, two-, three- and four-bedroom units respectively¹⁸. Colorado-approved tiny homes also need to satisfy local land-use requirements for long-term occupancy³⁰.

1. Confirm the parcel's zoning district, overlays, permitted use, lot size, setbacks, and applicable lot coverage with Adams County Community & Economic Development^5,9,18,28.
2. If any work is in a floodplain, obtain the required Adams County floodplain-development permit³.
3. Submit the building application and required documents through the E-Permit Center¹.
4. Design to the 2024 International Codes now in effect for applications accepted on or after July 1, 2026¹.
5. If the parcel lacks public sewer, obtain the soils report and septic design, then submit the septic application and fee to the Health Department⁴.
6. For a new or replacement well, apply to the Colorado Division of Water Resources³¹.
7. Complete building and septic inspections, secure the septic use permit where applicable, and request the required certificate of occupancy through the E-Permit Center^4,10,16.

Adams County allows one ADU with a primary single-family home on an existing legal lot, subject to building, zoning and utility requirements⁹. The ADU minimum is 500 square feet; the size limit is 40% of the home's floor area or 750 square feet, whichever is greater, with a 1,500-square-foot detached maximum and possible further district restrictions⁹. A county Agricultural-3 variance case uses a 750-square-foot maximum, so ask Community & Economic Development which cap applies to your design^5,27. Water-district properties need a will-serve letter for an ADU; well and septic properties may need proof the well supports multiple units and a new or updated septic permit⁹. New or replacement wells require a Colorado Division of Water Resources permit⁷. Check floodplain status and whether a proposed land division requires subdivision review before closing^3,32. Direct state-highway access requires a state access permit; we could not confirm the complete county driveway-permit rule, so ask Community & Economic Development about local-road access^5,33. The median annual property-tax bill is about $2,770²⁹.