An ADU in Boulder County is not a by-right use — it requires discretionary review and is limited to specific purposes. Here is what the code actually allows, cited, so you know before you invest.
Every figure below is drawn from Boulder County's adopted ADU regulations. The exact setbacks for your parcel depend on its zoning — the ADU finder reads them off your parcel.
Permitted by right
No — special review
Requires a discretionary review; may be limited to specific unit types.
Maximum size
Up to 700 sq ft
By type: family-care unit ≤ 700 sf; agricultural-worker unit ≤ 1,800 sf (Agricultural / Rural Residential districts); historic unit = the existing landmarked structure's size. Boulder County LUC §4-516.
Owner-occupancy
Required
The property owner must live on the property.
Off-street parking
1 space
Setbacks
Your zone's accessory setbacks
A detached ADU follows this city's accessory-structure setbacks, which vary by zoning district. Enter your address in the ADU finder and we'll pull your parcel and show the exact side, rear, and front lines on it.
Source
Boulder County Land Use Code (May 13, 2025), Article 4 §4-516 (Accessory Uses — Accessory Dwelling). An accessory dwelling is NOT a by-right use: it is allowed ONLY by Limited Impact Special Review (discretionary), and ONLY as a family-care unit, an agricultural-worker unit, a historic-landmark unit, or a disaster-recovery unit — not as a general/market-rate rental ADU. Boulder County is NOT an HB24-1152 subject jurisdiction (DOLA Multilaw = 'Exempt: may opt-in'), so the statewide by-right ADU law does not apply.
This is a plain-language summary for planning, not a legal determination. Codes are amended; confirm the current requirements with Boulder County and a design professional before you rely on them.
A subject jurisdiction must allow at least one ADU by right (administrative — no discretionary review or public hearing) on any lot where a single-unit detached dwelling is an allowed use, and may not impose owner-occupancy mandates, ADU-specific minimum lot size, parking minimums (narrow exceptions only), or design standards stricter than the primary dwelling. It took effect June 30, 2025. That is why cities like Boulder County now approve a backyard home administratively — and why owner-occupancy and parking mandates are largely gone.
We keep cited ADU rules for every city below. Switch to yours.
Enter your address and we pull your parcel lines and your district’s ADU setbacks. Trace your house, place one of our plans, and see what fits and what it would cost — in a few minutes.
Keep exploring
ADU rules by city
Cited, city-by-city ADU rules across the Front Range.
Questions answered
Allowed, how big, what it costs, how long — answered from the adopted codes.
How the finder works
What to type, what you get back, and what it deliberately will not tell you.
Rental income potential
Rent, resale value, and what a permitted second unit adds to your property.
ADUs for family
Aging parents, multigenerational living, childcare.
How to finance an ADU
HELOC, construction loans, and CHFA options.
Process & timeline
What to expect from contract to move-in.
Floor plans & pricing
Five plans, three finish grades, five architectural styles.
About Addwell
Who we are and how we build.