Detached backyard cottage
A detached ADU can be attractive because it creates physical separation from the main home. It can also concentrate cost in foundations, utilities, trenching, access, fire separation, and site work.
Garage conversion or garage apartment
Garage projects can look efficient when there is an existing structure or alley access. They still need careful review of structural condition, ceiling heights, access, utilities, parking, fire separation, and whether the existing building is worth converting.
Basement or internal ADU
Internal units can avoid some site-work costs, but they can raise egress, ceiling height, fire separation, privacy, parking, utility separation, and owner-comfort questions.
Attached addition
An attached ADU can sometimes fit where a detached structure cannot. It may also complicate circulation, privacy, existing-home construction, foundation tie-ins, and long-term use.
Local terminology matters
Some local materials may use different terms. Larimer County materials, for example, reference Accessory Living Areas in specific county contexts, but Civic Infill Works generally uses ADU for public-facing clarity.
Local starting points include Larimer County Accessory Living Area information and Fort Collins ADU information.