A basement ADU is a separate dwelling built inside your home's lower level. Colorado's HB24-1152 counts internal ADUs alongside attached and detached ones, as of October 2026. In Denver, a basement unit goes through the same zoning, building and sewer permits as other ADUs.
Is a basement ADU allowed in Denver?
Colorado's HB24-1152 requires subject jurisdictions, including Denver, to allow one ADU with a single-unit detached home, and it names internal ADUs as one of the forms. Denver's ADU page describes one attached or detached ADU per single-unit house. We confirm with Denver how a lower-level unit is classified for your zone district before design. Read the basement ADU guide for the detail.
What does a basement need to become an ADU?
- Egress. Sleeping rooms need an escape window or door, which often means cutting a larger window well.
- Headroom. Ceiling height under ducts and beams has to meet the residential code.
- Separation. A fire-rated ceiling and doors between the two units.
- Its own entrance. Usually an exterior stair or a shared vestibule with locking doors.
- Moisture. A dry basement before any finishes go in.
Does a basement ADU need its own address and meters?
It needs its own address: Denver requires every ADU to have one, as of October 2026. Separate meters are a different question. Denver Water may require a new license for ADU water service, with possible fees, and we check gas and electric options with the utility during design.
What does a basement ADU cost?
Block Renovation's 2026 national figures put basement conversions at about $50,000 to $120,000. We found no Denver-only range. The cost climbs when a new egress well, a separate furnace or a sewer ejector pump is needed.
Who can do the work?
Denver says ADUs must be built by a licensed contractor, and homeowners cannot apply for ADU permits themselves, as of October 2026. We hold the permits and coordinate the inspections.