Often, yes. As of October 2026, Colorado's HB24-1152 lists internal ADUs among the forms covered cities must allow, and Denver permits ADUs through zoning, building and sewer permits. Whether your basement works depends on headroom, egress, a separate entrance and fire separation from the main home.
What does the building code look for?
- Emergency escape. Every sleeping room needs an egress window or door.
- Ceiling height. Ducts and beams often set the real limit in older basements.
- Fire separation. A rated ceiling and doors between the units. Arvada, for example, requires a 1-hour separation with a sound rating of STC 45 or more.
- Heating and ventilation. Some cities require a separate HVAC system for the ADU.
- Plumbing. Fixtures below the sewer line may need an ejector pump.
What paperwork does Denver require?
As of October 2026, Denver's ADU page lists zoning, building and sewer use and drainage permits, trade permits and a certificate of occupancy before anyone moves in. The ADU must have its own address, and the work must be done by a licensed contractor.
How is a basement unit classified?
It depends. Denver's ADU page describes attached and detached ADUs; the state law separately names internal ADUs. We confirm with Denver how a lower-level unit is treated in your zone district before design, because that affects which standards apply.
What does it cost?
Block Renovation's 2026 national range for basement conversions is about $50,000 to $120,000; we found no Denver-only figure. A new egress well, an exterior stair, a second furnace or an ejector pump each add to the total. See the Denver cost guide.
Is a basement unit a good rental?
It can be, especially near transit and campuses, but light, ceiling height and sound control matter to tenants. See ADU rent in Denver.
Sources, as of October 2026:
- Colorado Department of Local Affairs, Accessory Dwelling Units page, for internal ADUs under HB24-1152.
- City and County of Denver, Permitting an Accessory Dwelling Unit, for permits, address and contractor rules.
- City of Arvada, Accessory Dwelling Units page, for its separation and HVAC requirements.
- Block Renovation, “A Deep Dive Into ADU Construction Costs” (2026).