ADU Builders in Boulder, Colorado
Your ADU, done right the first time.
An ADU is a small building with an outsized impact on your life. A guest house where your parents can stay three weeks a year without anyone losing their mind. A rental that pays down your mortgage. A quiet home office that's actually a separate place. A future home for the kid who'll be applying to college faster than you'd like. Whatever it becomes, it's on your property, connected to your main house, and permitted to be lived in. (If you're thinking bigger, we also work as custom home builders in Boulder, Colorado, which is a different conversation but often overlaps.)
That last part matters. Boulder County and the City of Boulder have specific, and evolving, rules about ADUs. Lot size minimums. Owner-occupancy requirements. Parking. Licensing. Saturation limits by neighborhood. Done wrong, you end up with a structure that can't be legally rented, or worse, can't legally be occupied. Done right, you've added real equity to your property and flexibility to your life.
Why people build ADUs around here
Boulder isn't getting cheaper, and the land isn't getting more plentiful. For a lot of our clients, an ADU is the most practical move on the board. It adds usable square footage without moving. It creates income or saves on rent for a family member. It lets you stay in the neighborhood you love.
I've built ADUs used as short-term rentals (where the zoning allows), long-term rentals, mother-in-law suites, artist studios, and home offices for people who learned during the pandemic that they never want to commute again. The right ADU depends on what you actually need it to do for you.
How Your ADU Comes Together
We take ADUs from the earliest feasibility question all the way to final inspection.
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Feasibility and zoning review, can your lot support an ADU, and what kind
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Site plan, floor plan, and elevations
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Interior design and finish selections (flooring, countertops, fixtures, cabinetry)
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Permitting through the City of Boulder, Boulder County, or your local jurisdiction
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Utilities, excavation, and foundation work
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Framing, mechanicals, insulation, drywall, and finishes
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Landscaping tie-in and final inspections
If you already have design partners, bring them. If not, we'll bring in GFE Structural and Re-Find Spaces. The point is a permitted, well-built structure you can actually use for the thing you built it for.
Attached or Detached
Attached ADUs (sometimes called "bump-outs") share a wall with the main house. They're often the best option on smaller Boulder lots where setbacks are tight. Detached ADUs stand alone and tend to feel more like a separate home, which matters if you're housing tenants or adult family members.
Garage conversions and above-garage ADUs are common on tight lots. Basement conversions are another path (see our basement refinishing in Boulder page). Larger lots in Niwot, Gunbarrel, and Lyons usually have room for a fully detached new build. We'll walk your property and tell you honestly what makes sense.
Related Services
Tight Lines Construction specializes in custom ADU construction in Boulder, Colorado, helping homeowners create flexible, thoughtfully designed living spaces that add function and value to their property. In addition to attached and detached ADUs, our team provides home remodeling, additions, commercial remodeling, custom home building, and basement refinishing throughout Boulder and the surrounding Front Range. Whether you’re creating space for family, a private guest suite, a home office, or simply making better use of your property, we bring experienced project management, quality craftsmanship, and clear communication from start to finish.
Frequently asked questions about Boulder ADUs
Is my Boulder lot eligible for an ADU?
Depends on your zone, your lot size, and your neighborhood's ADU saturation. The City of Boulder has minimum lot sizes that vary by zoning district, and some neighborhoods have reached their ADU cap. Boulder County rules differ. We can pull the zoning on your address and give you a straight answer before you spend a dollar on design.
Do I have to live on the property if I build an ADU in Boulder?
Within the City of Boulder, yes. Owner-occupancy is currently required for licensed ADUs, which means either you live in the primary residence or in the ADU. Rules have shifted over the years and may shift again, so we'll confirm what's current when we run your feasibility.
Can I rent my ADU on Airbnb?
Short-term rentals in Boulder are regulated and limited. In most cases, you need a short-term rental license, and those come with their own requirements and caps. Long-term rentals (30 days or more) are generally easier. We'll walk through the options with you.
How much does an ADU cost to build in Boulder?
Most detached ADUs in Boulder County run somewhere between $400K and $800K and up, depending on size, finishes, site conditions, and how your utilities tie in. Garage conversions and basement conversions can come in lower. We'll give you a real range after we see your property.
How long does an ADU build take?
Most ADUs run 10 to 16 months from design kickoff to move-in, with permitting taking anywhere from a few months to close to a year in the city. We build the realistic permitting timeline into your schedule so you're not guessing.
Where We Build ADUs
From our Boulder office, we build ADUs across the Front Range. Boulder, Longmont, Lafayette, Louisville, Erie, Superior, Broomfield, Lyons, Niwot, Gunbarrel, and throughout Boulder, Broomfield, Jefferson, Larimer, Weld, Adams, and Denver counties.
