Short answer: Colorado ADUs typically cost $190 to $625+ per square foot depending on type, with most 500–650 sq ft projects landing between $120,000 and $400,000 all-in. Colorado’s statewide ADU law (HB24-1152) has also made permitting easier in many cities by limiting parking mandates and owner-occupancy requirements. Josh Brooks Construction and Renovation Inc. is a licensed, local general contractor (Boulder County license CON-24-0152) building additions and ADUs across the Front Range since 2014.
Call 720-828-7997 | Text 720-453-5095 | joshbrooksconstruction@gmail.com
How much does an ADU cost to build in Colorado?
Cost per square foot varies a lot by ADU type:
- Basement/interior conversion: $190–$330/sq ft
- Garage conversion: $230–$370/sq ft
- Prefab/modular: $275–$500/sq ft
- Attached ADU: $300–$490/sq ft
- Above-garage addition: $340–$600/sq ft
- Detached new-build: $380–$625+/sq ft
As total project cost, a typical 650 sq ft unit runs roughly:
- Garage conversion (500 sf): $120,000–$175,000
- Basement conversion (650 sf): $125,000–$190,000
- Attached ADU (650 sf): $200,000–$300,000
- Above-garage (650 sf): $230,000–$365,000
- Detached ADU (650 sf): $250,000–$400,000
Across all types, Colorado ADU projects generally fall between $110,000 and $500,000 depending on size, site conditions, and finish level.
What is Colorado’s new ADU law and how does it change permitting?
Colorado’s statewide ADU law, HB24-1152, applies to many cities and counties and generally prohibits requiring extra off-street parking for an ADU and prohibits owner-occupancy mandates in jurisdictions it covers. It also pushes cities toward administrative approval — reviewed against clear, objective standards — rather than a discretionary hearing process. In practice this has shortened timelines in several Front Range cities, though every jurisdiction implements it a little differently, so local rules still matter.
How does the process differ across Boulder, Weld, Larimer, Jefferson, and Douglas counties?
ADU and addition rules are set at the city or county level, so requirements on lot coverage, setbacks, maximum square footage, height limits, and design review vary block by block, not just county by county. Some Front Range cities cap ADU size as a percentage of the primary home’s footprint; others set a flat square-footage maximum. Before you settle on a design, we pull the specific zoning and building requirements for your address — not a generic county summary — since two homes a mile apart can fall under different rules.
How long does an ADU or addition take from permit to move-in?
Permitting alone typically takes 1–3 months depending on the jurisdiction and how administrative (versus discretionary) the review process is. Construction adds another 4–9 months depending on ADU type — garage and basement conversions move faster than ground-up detached units, which require full foundation, framing, and utility work.
ADU vs. home addition: which makes more sense?
An addition expands your existing living space — a bigger kitchen, a primary suite, more square footage under one roofline — and is typically less expensive per square foot since it ties into existing systems. An ADU creates a separate, independently livable unit with its own kitchen and bathroom, useful for rental income, multigenerational living, or long-term flexibility, but it involves more code requirements (separate egress, sometimes separate utility metering, fire separation). The right choice depends on whether you need more space for your household or a self-contained unit you can rent out or hand off to family.
Do ADUs increase property value and can they generate rental income?
ADUs can add meaningful resale value and, when permitted for rental use, ongoing income potential — though actual returns depend heavily on your neighborhood’s rental market and local short-term or long-term rental rules, which vary by city. Talk to a local real estate professional about resale comps in your specific area before finalizing size and finish level, since over-building for the neighborhood rarely pays back dollar for dollar.
What areas do you build ADUs and additions in?
Josh Brooks Construction and Renovation Inc. builds ADUs and home additions across the Front Range — Boulder, Weld, Larimer, Jefferson, and Douglas counties — including Longmont, Boulder, Fort Collins, Loveland, Greeley, Erie, Firestone, Brighton, Thornton, Westminster, Golden, Arvada, and the greater Denver metro. Every trade is in-house, and Josh personally supervises each build.
Get a free ADU or addition consultation
We’ll walk your property, check what your specific lot allows, and give you a written, locked price within 24 hours:
Call 720-828-7997
Text 720-453-5095
Email joshbrooksconstruction@gmail.com
Licensed, local, and building on the Front Range since 2014. Veteran and senior discounts applied automatically.
Frequently asked questions
How much does it cost to build an ADU in Colorado?
Colorado ADUs typically cost $190 to $625+ per square foot depending on type, with most 500-650 sq ft projects landing between $120,000 and $400,000 all-in, and the overall range across all project types spanning roughly $110,000 to $500,000.
What is HB24-1152 and how does it affect ADU permitting in Colorado?
HB24-1152 is Colorado’s statewide ADU law. In jurisdictions it covers, it generally prohibits requiring extra off-street parking and owner-occupancy mandates for ADUs, and pushes cities toward administrative approval based on objective standards rather than discretionary review, which has shortened timelines in many Front Range cities.
Do I need a permit to build an ADU or addition in Colorado?
Yes. Both ADUs and home additions require building permits, and ADUs typically also require zoning approval confirming lot size, setbacks, and unit size comply with local rules, which vary by city and county.
How long does it take to build an ADU?
Permitting typically takes 1-3 months, and construction adds another 4-9 months depending on ADU type, with garage and basement conversions generally faster than ground-up detached units.
Which is cheaper, an ADU or a home addition?
A standard home addition is usually less expensive per square foot than an ADU because it ties into your home’s existing kitchen, bathroom, and utility systems, while an ADU requires its own independent systems and code compliance as a separate living unit.
Do you build ADUs and additions?
Yes. Josh Brooks Construction and Renovation Inc. designs and builds ADUs and home additions across the Front Range, with every trade in-house and owner-supervised construction. Call 720-828-7997 or text 720-453-5095 for a free consultation.
Sources & references
Josh Brooks Construction and Renovation Inc. backs the guidance on this page with authoritative sources:
