Can I Build an ADU on My Property? Start With the Parcel

State permission is the floor—not the finished answer

Colorado's ADU law applies to defined “subject jurisdictions.” Beginning June 30, 2025, those jurisdictions must allow one ADU as an accessory use to a single-unit detached dwelling wherever that dwelling type is allowed, subject to an administrative approval process.

That matters because it changes the starting presumption. In a covered jurisdiction, the conversation should begin with how the property can comply—not with a discretionary public hearing about whether an ADU belongs in the neighborhood.

But the state rule is not a building permit and it is not a promise that every idea fits. Local governments can still apply objective standards, and the proposed unit must still move through the applicable zoning, building, utility, fire, and other reviews. Properties outside the statute's defined jurisdictions may follow a different local framework.

First, identify the authority that governs the address

A mailing address is not a permit answer. A property that uses a familiar city name may sit inside that city, in unincorporated county territory, or near a boundary where the governing rules change from one parcel to the next.

Start by confirming the authority having jurisdiction: the city or county that controls zoning and reviews the permit. Then confirm the property's zone district, the code and amendments currently in effect, and any separate overlay or review that applies.

Denver illustrates why this matters. The City and County of Denver reviews projects against its building and fire code, zoning code, and related regulations. Denver also has two zoning-code systems, and landmark properties or properties in historic districts can have added design review. Those facts are useful for a Denver address; they do not automatically describe Lakewood, Arvada, Littleton, or another Front Range jurisdiction.

• Confirm the legal jurisdiction—not only the postal city.
• Find the parcel's zone district and applicable zoning code.
• Check for landmark, historic, floodplain, planned-development, or other overlays.
• Verify the effective building code and local amendments before design begins.

Then test what the parcel can physically carry

Once the governing rules are clear, the property itself gets a vote. Lot width and depth, the placement of the existing home, setbacks, allowable coverage, easements, grade, drainage, mature trees, alley or street access, and the route to utilities can all shape the viable building envelope.

This is where a quick yes-or-no answer becomes a useful feasibility study. A detached unit may be permitted in principle but difficult to place without compromising access or running services an impractical distance. An over-garage unit may preserve yard area but introduce structural, stair, and height questions. An internal or attached unit may fit the lot more easily while creating a different set of life-safety, privacy, and building-system decisions.

The sequence matters: establish the envelope first, then choose the ADU type and floor plan. Drawing the ideal unit before the parcel screen is how homeowners pay to redesign the same project twice.

• Existing house and accessory-building locations
• Setbacks, lot coverage, height, and buildable envelope
• Easements, trees, grade, drainage, and site access
• Water, sewer, electrical, gas, and mechanical-service routes
• Structural capacity when converting or building over an existing space
• The intended use of the unit and the reviews that use may trigger

Choose the ADU type after the constraints are visible

“ADU” describes a second dwelling, not one construction method. The practical options generally include a detached backyard unit, a unit above a garage, a garage conversion, a basement or internal conversion, or an attached multigenerational unit.

Each uses the property differently. A detached unit needs a location, foundation, access, and service route. An over-garage unit asks whether the garage and its foundation can support residential space—or whether a new structure makes more sense. A conversion works inside an existing footprint but must still satisfy the requirements for a dwelling rather than merely a finished room.

AAA's commercial ADU guide explains the different project types. This article has a narrower job: help you establish which options survive the property screen before you invest in a detailed design.

A real Denver ADU shows what feasibility looks like in the ground

On AAA Home Improvements' published Denver pop-top and whole-home remodel, the ADU was a two-bedroom unit above a new detached two-car garage. The old carport came out, the new garage and dwelling were built at the rear of the lot, and separate services were trenched across the yard. The work was permitted through the City and County of Denver and inspected through the build.

The lesson is not that every property should receive an ADU over a garage. It is that a detached ADU is a small building: it needs a structure, a workable place on the lot, service connections, access, coordinated plans, and inspections. The correct type emerged from the site and the larger project scope—not from choosing a floor plan in isolation.

That project is documented from demolition through completion on AAA's Denver pop-top, detached ADU, and whole-home remodel page. It is useful proof of the construction sequence, not a zoning precedent for another address.

Bring these facts to the first feasibility conversation

You do not need a finished design to get a better first answer. You do need enough property information to prevent the conversation from becoming guesswork.

With those inputs, a contractor or designer can identify the questions that deserve real investigation before design fees grow. The outcome may be a clear path, a choice between two ADU types, or a constraint that makes a different kind of addition the better investment. Any of those is more valuable than a confident answer made without the parcel.

• The property address and any survey you already have
• Your intended use: family housing, long-term rental, workspace, or another goal
• The ADU type you are considering—without treating it as fixed
• Known easements, HOA or planned-development documents, and historic status
• Photos of the yard, garage, basement, access points, and utility locations
• Your target size, must-have rooms, timing, and realistic investment range

The answer should be specific before the design is

A responsible feasibility answer names the jurisdiction, the parcel constraints, the viable ADU type, and the issues that still need confirmation. It does not promise a size, cost, schedule, or rental outcome from a city name alone.

Colorado's statewide changes mean more homeowners have a legitimate path to an ADU. The best way to use that opportunity is to start in the right order: jurisdiction, parcel, type, systems, then design.