Boulder allows a detached accessory dwelling unit by right on most single-family lots. Here is exactly what the code permits — size, setbacks, parking, and owner-occupancy — each point cited to the adopted regulations.
Every figure below is drawn from Boulder's adopted ADU regulations. The exact setbacks for your parcel depend on its zoning — the planner reads them off your lot.
Permitted by right
Yes
Approved through the normal building-permit process — no discretionary hearing.
Maximum size
Up to 800 sq ft
Detached ADU ≤ 800 sf (1,000 sf for a deed-restricted affordable ADU or on a designated historic property). Attached ADU ≤ one-half the principal structure's floor area or 1,000 sf, whichever is less (750 sf if the principal has < 1,500 sf). BRC §9-6-3(n), Table 6-3.
Owner-occupancy
Not required
You don't have to live on-site — Colorado's HB24-1152 bars owner-occupancy mandates for subject jurisdictions.
Off-street parking
None required
No ADU off-street parking minimum: Boulder's ADU guide and §9-6-3(n) impose no ADU parking requirement, and (as a DOLA-certified HB24-1152-compliant subject jurisdiction) Colorado HB24-1152 (C.R.S. §29-35-403) bars parking minimums. Narrow exception — up to one space may be required only where the lot has no existing off-street parking, its zoning required off-street parking for the principal dwelling as of Jan. 1, 2024, and on-street parking is prohibited on the abutting block.
Setbacks
Your zone's accessory setbacks
A detached ADU follows this city's accessory-structure setbacks, which vary by zoning district. Trace your lot in the planner and we'll show the exact side, rear, and front lines on your parcel.
Source
Boulder Revised Code §9-6-3(n) (ADU = permitted accessory use [A] in the residential districts; Table 6-3 size limits). Approved through the regular building-permit process — NO prior administrative/discretionary review since Sept. 1, 2023, and the ADU saturation cap was removed the same date; owner-occupancy removed eff. March 8, 2025 (Ord. 8650), per Colorado HB24-1152. DOLA Multilaw Applicability = 'Required' (Subject Jurisdiction); DOLA-certified ADU Supportive Jurisdiction.
This is a plain-language summary for planning, not a legal determination. Codes are amended; confirm the current requirements with Boulder 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 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.
Draw your lot and house on the satellite map, drop an ADU, and see the setbacks and a budget range on your own property — in about a minute.
Keep exploring
ADU rules by city
Cited, city-by-city ADU rules across the Front Range.
Rental income potential
Real numbers on what ADUs earn.
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
Three sizes, three tiers, two styles.
About Addwell
Who we are and how we build.