Colorado ADU Cost Calculator

What Does It Cost to Build an ADU in Colorado?

Colorado's construction cost sits modestly above the national baseline — about 12% — with the Front Range cities (Denver, Boulder, Fort Collins, Colorado Springs) accounting for most of that premium. A detached 800-square-foot ADU in Denver typically runs $200,000–$300,000 for standard finishes, with Boulder often $20,000–$40,000 higher due to stricter design review and a much tighter labor market. Colorado Springs, Fort Collins, and Greeley come in at $170,000–$250,000 for the same build. Western Slope (Grand Junction, Glenwood Springs, Montrose) and Eastern Plains cities are materially cheaper — often $140,000–$210,000 — but labor is scarcer and schedules can stretch. Garage conversions run $90,000–$170,000 and are particularly efficient in Denver, where many older lots have a detached garage on an alley that converts cleanly into an ADU with access separated from the primary dwelling.

Colorado-Specific Cost Drivers

Three factors push Front Range Colorado costs above baseline. First, snow-load structural requirements — Denver and the mountain front cities use ground snow load values of 30–50 psf (or higher at altitude), which drives heavier roof framing, engineered trusses, and stronger shear walls than Texas or Florida builds. Second, high-altitude IECC compliance — Colorado's energy code requires more insulation in envelope assemblies because heating load at altitude is significant, and many jurisdictions have adopted net-zero or stretch codes that require heat pump HVAC, high-R windows, and tight envelope construction. Third, water rights and stormwater management — the City of Denver's Green Buildings Ordinance and similar Fort Collins / Boulder rules require stormwater and sometimes water-conservation features that non-Colorado states rarely see. Offsetting, Colorado has no hurricane exposure, seismic requirements are modest, and the state's building departments are generally efficient.

Denver, Boulder, and the Rest

Denver's 2023 zoning code updates expanded ADU eligibility to most residential districts and introduced a permit-expediter lane for standard ADU designs. Permit fees typically run $2,000–$5,000, with plan review in 6–12 weeks. Boulder has one of the most involved ADU permitting processes in Colorado — design review, affordable-housing linkage requirements for certain project types, and stricter site-constraint rules push timelines to 6–12 months and permit costs to $4,000–$8,000. Fort Collins and Colorado Springs have permissive ADU ordinances with faster processing. Aurora and Lakewood have more limited ADU allowances. Mountain resort towns (Aspen, Vail, Breckenridge, Steamboat Springs) have their own severe-climate and second-home-market dynamics — costs run sharply higher there and are not well represented by the statewide 1.12 multiplier. Timeline from architect-hire to certificate of occupancy is 5–9 months in the Front Range and 6–11 months in Boulder specifically.