Accessory Dwelling Units, also known as granny flats, carriage houses or casitas, are built on the same property as primary residences and serve as suites for visitors, aging parents or rental properties. If you’re flirting with the idea of an ADU on your property, you must follow strict guidelines promulgated by your local Planning & Zoning Dept.

Your zoning, lot size and homeowners’ association rules are only the start of due diligence. Especially if you are on a well & septic, you need to be certain the well yield/permit and septic capacity meet requirements. And there rules to follow after you’ve added an ADU. Here are some insights from the Jeffco P&Z website (residents of Park & Clear Creek counties should consult their planning commissions):

• ADUs should generally be attached to or located within 50’ of the residence.
• ADUs should use the same driveway as the residence for access.
• The maximum size of an ADU is determined by whether it is attached to the main residence and the lot size.
• Up to 3 people may live in the ADU, and no more than 6 unrelated individuals may live on the property, including the primary home & the ADU.
• ADUs can only be rented ‘long term’, they cannot be rented for less than 30 days. Therefore, they cannot be listed on AirBNB.
• The property owner must live in either the primary residence or the ADU.
• The ADU cannot be sold separately, it is part of the residence’s property.
• The height of the ADU cannot generally be higher than the residence, over-garage units must generally be 25 feet or less in height.

Here’s more about ADUs from Jefferson County: Accessory-Dwelling-Unit-ADU (jeffco.us). You should plan on a lengthy, detailed review of your plans by your county planning commission and building department. And you should check with your HOA to be sure ADUs are approved.