ADU builder in Boulder County & the Denver metro
An accessory dwelling unit, or ADU, is a second, smaller home on the same lot as a single-family house: a backyard cottage, an apartment attached to the house, a converted garage or a basement apartment. We plan it with you, bring in the engineering, handle the permits and build it.
What we handle
- Your city's ADU rules, checked first
- A detailed 3D model, drawn by Alex
- Engineering where the design needs it
- Permits and inspections
- The build, run by the owners
Can I build an ADU on my lot?
In most of the towns we work in, a 2024 state law made that question easier to answer. Colorado's ADU law, House Bill 24-1152, requires cities and towns including Boulder, Longmont, Louisville, Superior, Erie, Broomfield, Westminster, Arvada, Thornton, Lafayette, Northglenn and Denver to allow one ADU with a single-family home on most lots.
Since June 30, 2025, the law has required those cities to approve an ADU that meets their rules by staff review rather than a public hearing. That doesn't mean anything goes: each city still sets its own rules, such as size and height limits, though the state law caps how strict some of them can be.
Outside city and town limits, unincorporated Boulder County has its own ADU rules, so a rural address follows a different path. Either way, we look up the rules for your address before Alex starts drawing.
Four ways to add a second home
Which one fits depends on your lot, your house and your city's rules.
Detached backyard ADU
A small house of its own in the backyard, with its own foundation, roof and utilities. Of the four types, it takes the most building.
Custom home buildingAttached ADU
Built onto the house like an addition, with its own entrance, kitchen and bathroom.
Home additionsGarage conversion
An existing garage turned into living space. The walls and roof are already there; the floor, insulation, windows and utilities usually need work.
Basement apartment
A finished basement with its own kitchen, bathroom and entrance. Each bedroom needs an emergency escape opening, usually an egress window, which we can cut into an existing foundation.
Basement finishingFrom the rules to the final inspection
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Rules & lot check
We look up your city's ADU limits for your lot and walk it with you.
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3D model & engineering
Alex draws the ADU as a detailed 3D model so you can see the layout. Where the design needs it, an engineer designs the foundation and framing. Like an addition, an ADU also needs a full set of plans for the permit.
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Permits
We handle the permit application and see it through review.
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Build & inspections
The owners run the build from the foundation to the finish, with each inspection the permit calls for along the way.
Built from work we already do
An ADU combines kinds of work we already take on. A detached ADU is a small new home, and we built a custom home in Arvada from the ground up. An attached ADU is built the way we build home additions, and a basement apartment starts as a basement finish.
Most of an ADU stays in our hands. Alex and Sergei frame it, run the plumbing and wiring under their Colorado licenses, hang the drywall and set the tile. Our own painting crew does the paint, and for the foundation and the roof we bring in the concrete and roofing crews we use regularly.
ADU questions
Do I need a public hearing to build an ADU?
Usually not. Since June 30, 2025, the 2024 state law has required the cities it covers to approve an ADU that meets their rules through staff review. A house in a local historic district can still go before the city's historic preservation board. Unincorporated Boulder County has its own process, so it matters which one your address falls under, and we can check that for you.
How big can my ADU be?
Your city sets the size limit, so it varies from town to town, but in the cities the 2024 state law covers, the law keeps that limit from being too strict. Height and setback rules vary too. We check the limits for your lot before the design starts, so the plan begins inside them.
Can I turn my garage or basement into an ADU?
Often, yes. Both use space you already have, but the result still has to meet your city's ADU rules and the building code, including egress windows for basement bedrooms. We look at the space and the rules together at the walkthrough.
Is an in-law suite the same as an ADU?
It can be. An in-law suite with its own kitchen may count as an ADU under your city's rules, and then the ADU limits apply. Without a kitchen it is usually built as an addition or a basement finish; see in-law suites on our home additions page.
How much does an ADU cost?
There's no standard price for an ADU: the type, your lot and your city's rules all change the number. Your written line-item estimate, sent after the walkthrough, breaks it down part by part.
Thinking about an ADU?
Send your address and a few photos of the spot you have in mind. We'll check your city's rules, set up a walkthrough and follow up with a written estimate.