This page describes the kinds of financing homeowners use for an ADU, and the one state program tied to where you live. It carries no figures: no costs, no rates, no rents and no returns. Those depend on your property, your lender and a market none of us controls.
Why we will not estimate#
An ADU's cost turns on site conditions, utility work, the design and the moment you build. Published averages and per-square-foot rules of thumb are routinely wrong by amounts that matter. We would rather tell you what drives the number and let a builder price your actual site.
The same goes for rent. We describe what the rules permit, never what a unit might earn.
The common routes#
Cash or savings. No financing costs, no lender conditions, and no schedule imposed by anybody else.
Home equity: a line of credit or a loan. The most common route, because an ADU is a home improvement on a property you already own. A line of credit draws as the work progresses; a loan lands as one lump.
Cash-out refinance. Replaces the existing mortgage with a larger one. Its attractiveness depends entirely on how your current rate compares with today's.
Renovation or construction loans. Structured around the build, released in stages against inspections. More administration, and designed for exactly this.
Contractor or manufacturer financing. Sometimes offered directly. Worth comparing against a bank on total cost, not on the monthly payment.
The state programs#
Colorado created financing help for ADUs, but access depends on where your property is: Homeowners in certified ADU Supportive Jurisdictions can use CHFA ADU finance programs through participating lenders.
The determining factor is whether your jurisdiction has been certified. For the City of Boulder that is something we are still confirming: Being confirmed with State of Colorado.
For unincorporated Boulder County, the same certification question is open, and it also governs whether the state HOA protections apply: Being confirmed with State of Colorado.
Until those are confirmed, do not assume the CHFA programs are available for a Boulder County property. Ask the lender, and ask the Department of Local Affairs.
The affordable ADU route in the City of Boulder#
The City of Boulder allows a larger unit in exchange for an affordability commitment. The size allowance is Attached up to the lesser of two-thirds of the principal dwelling or 1,200 sq ft (750 sq ft if the principal is under 1,125 sq ft); detached up to 1,000 sq ft, and the commitment is Rent capped at 75% of area median income, with a Declaration of Use recorded against the property.
That is a genuine trade: more building, less rent, recorded against the property. Whether it suits you is a decision to make with a lawyer, because a Declaration of Use runs with the land.
Fees you should ask about early#
Fees are part of the budget and they are set by the jurisdiction, not the builder. In the City of Boulder we are still confirming the published figures: Being confirmed with City of Boulder, and Being confirmed with City of Boulder.
If you intend to rent the unit, there is also a license fee: Being confirmed with City of Boulder.
Where to go next#
What drives ADU cost in the City of Boulder breaks down the components without putting numbers on them. Renting an ADU covers the licensing rules.