Why ADU's Are a Good Idea... Especially in Colorado
- simon59675
- Dec 17, 2025
- 4 min read
Accessory Dwelling Units (ADUs) are becoming an increasingly important part of housing conversations in Denver and across the United States. While they may feel new to many homeowners along the Front Range, ADUs have been shaping neighborhoods in cities like Portland for decades.
My career and life have taken me to cities with very different urban design strategies, from the historically layered streets of Boston to the surprising density and structure of Honolulu. Each city expresses its values through how it plans, builds, and uses space. That is one reason I travel whenever time and finances allow. Cities reveal who they are and their values most clearly when you experience them in person (more on this in future posts).
Recently, while working on an ADU for a client, I was struck by how unfamiliar the concept still feels in Denver compared to Portland, another city I lived in not long ago. In Portland, ADUs quietly blend into neighborhoods, woven into the fabric of residential streets in a way that feels both intentional and unremarkable. So why does Denver feel so far behind?
The short answer is policy and time.
ADUs in Portland vs Denver
Portland
Portland began allowing ADUs citywide in the late 1990s and has steadily refined its regulations to encourage construction. Over time, the city removed owner occupancy requirements, eliminated off street parking mandates, and reduced development fees.
Today, Portland allows up to two ADUs on many residential lots, typically one internal or attached unit and one detached unit. These changes have led to widespread adoption, with several thousand ADUs now built across the city. Because the regulations have been in place for so long, ADUs are a familiar and accepted part of Portland’s housing landscape.
Denver
Denver is much newer to ADUs. While limited forms of accessory units existed earlier, meaningful expansion occurred in 2024 when the city legalized ADUs in nearly all residential zones. This change expanded eligibility from roughly one third of residential lots to approximately seventy percent citywide.
To date, Denver has permitted several hundred ADUs, with adoption accelerating as zoning changes take effect. Programs like Habitat for Humanity of Metro Denver’s ADU initiative help lower barriers by offering pre approved plans and financing support. These programs are especially useful for larger or less constrained lots, while custom design remains important for smaller or more complex sites.
What Is an ADU
An Accessory Dwelling Unit is a self contained residential space located on the same lot as a primary home. ADUs include a kitchen, bathroom, sleeping area, and independent access. They are sometimes called carriage houses, granny flats, or in law units.
ADUs cannot typically be sold separately from the primary residence, but they function as independent homes within an existing property.
Why ADUs Matter
Density Without Disruption
ADUs add housing incrementally. They allow neighborhoods to accommodate more people without introducing large apartment buildings or dramatically altering neighborhood character. This form of gentle density helps cities respond to housing demand while preserving the scale and social fabric of residential areas.
Efficient Use of Existing Infrastructure
ADUs rely on infrastructure that already exists, including streets, utilities, schools, and transit. This makes them one of the most resource efficient ways to add housing, particularly in established neighborhoods close to services and employment.
Flexibility for Changing Lives
An ADU can serve many purposes over time. It might house an aging parent, a caregiver, a renter, or an adult child transitioning into independence. That adaptability makes ADUs especially resilient investments for homeowners whose needs will change over decades.
Financial and Social Value
Construction costs for ADUs vary widely based on size, site conditions, and regulatory requirements. While rental income can help offset housing costs or provide long term financial stability, the social value is often just as important. ADUs support multigenerational living, proximity to loved ones, and stronger neighborhood connections.
My Perspective as an Architect
Living in Honolulu after growing up in New England highlighted the power of proximity. Multigenerational households were common, and daily life reflected a deep cultural value placed on family and mutual support. While the idea of ohana has been commercialized elsewhere, its authenticity in Hawaii is rooted in people living close enough to care for one another.
ADUs offer a way to support that kind of closeness within the context of American cities. They are not a single solution to the housing crisis, but they are a meaningful and human scaled tool.
If we thoughtfully integrate ADUs into our existing neighborhoods, we can strengthen both our urban fabric and our social connections. Small homes create the gentle density that a city like Denver craves. When placed carefully on a site and designed with integrity, craft, and creativity, they can have an outsized impact.
Frequently Asked Questions About ADUs
Are ADUs legal in Denver?
Yes. As of 2024, ADUs are allowed in most residential zones citywide, subject to zoning and design standards.
How many ADUs does Portland have?
Portland has several thousand permitted ADUs, built over more than two decades of supportive policy.
Do I need an architect to design an ADU?
Not always, but working with an architect is especially helpful for small lots, complex zoning conditions, or homeowners seeking a custom solution tailored to their site.
References and Sources
City of Portland Bureau of Planning and Sustainability Portland ADU zoning and development standardshttps://www.portland.gov/ppd/zoning-land-use/adu
City of Denver Community Planning and Development Citywide ADU text amendment and background reportshttps://www.denvergov.org/Government/Agencies-Departments-
Denverite Coverage of Denver ADU legalization and adoption trendshttps://denverite.com
Habitat for Humanity of Metro Denver
Single Family Plus ADU Program
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