Reimagining Urban Housing: The Rise of Single-Stair Apartment Buildings in Denver

As Denver confronts a mounting housing affordability crisis, a transformative new building typology has emerged: 5-story single-stair apartments. As mandated by Colorado’s statewide Bill HB25-1273, cities across the state are amending local building codes to permit five-story multifamily residential buildings served by a single exit stair. As the state’s largest city with the most acute housing crisis, Denver’s proposed amendments to the 2025 Denver Building and Fire Codes are critical to understand. This shift introduces a new typology into the local development toolkit, giving both market-rate real estate developers and affordable housing authorities a unique opportunity to reshape Denver’s urban fabric.

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A Building Code Change with Radical Design Implications

City officials are currently working to amend Section 1006.3.4 of the Denver Building Code. If adopted, single-exit residential buildings, also known as point access blocks, will be legalized under specific conditions:

  • Maximum 5 stories above grade (4 with an occupiable roof) and one basement
  • Four dwelling units per floor max, and 6,000 SF per floor
  • Type I, II, or IV construction with full NFPA 13 sprinkler coverage
  • 20-foot travel distance max from unit door to stair
  • Each unit must have an emergency escape & rescue opening
  • 1-hour rated corridors and 2-hour rated exit stairs/elevator shafts
  • Requirements for pressurized elevator shafts, smokeproof stairs, and manual fire alarms
  • Strict limits on shared lobbies, utilities, and obstructions near escape openings

In short, this is not a deregulation—it’s a precision regulatory tool that unlocks innovation while demanding high standards of life safety and performance.

Why Single-Stair Housing Matters

In Denver, it creates a missing middle product that bridges the gap between townhomes and large multifamily podiums. For developers, this means there are suddenly vastly more potentially buildable lots for creating successful projects. And for future residents, this means there may soon be a whole new segment of housing that is both affordable and livable.

  • Greater housing density on small infill lots
  • Lower construction costs relative to podium or double-loaded corridor buildings
  • More units with dual orientation for daylight and ventilation
  • Reduced shared circulation space, increasing net-to-gross efficiency
  • Enhanced livability and community interaction, particularly with atrium and courtyard schemes

Where to Look for Properties

Given the proposed amendments to the building and fire codes, there are currently 7 zone districts in Denver that are most likely to permit 5-story single-stair apartment buildings.

U‑RX‑5 (Urban Residential Mixed Use – 5 stories)

  • Allows mixed‑use buildings up to 5 stories. Suitable for purely residential as well.
  • Excellent—allows residential density and modest mixed‑use.

U‑MS‑5 (Urban Main Street – 5 stories)

  • Encourages ground-floor commercial with upper-floor residential, up to 5 stories. Strong fit for transit‑oriented developments.
  • Great for ground‑floor retail or amenity activation.

G‑MU‑5 (General Urban Multi‑Unit – 5 stories)

  • Intended to allow mid- to high‑density residential buildings up to 5 stories, regardless of ground-floor commercial.
  • Most flexible for pure residential configurations.

G‑RO‑5 (General Urban Residential Office – 5 stories)

  • Supports either residential or office buildings, up to 5 stories—less commonly used for multifamily.
  • Might be a good district to find underutilized lots.

G‑RX‑5 (General Urban Residential Mixed‑Use – 5 stories)

  • Similar mixed‑use district with residential emphasis.
  • Good for smaller residential and live/work models.

C‑RX‑5 (Urban Center Residential Mixed‑Use – 5 stories)

  • Ideal for dense mixed-use corridors, transit-oriented developments, or neighborhood nodes.
  • Strong for transit-aligned and higher density infill.

C‑MX‑5 (Urban Center Mixed‑Use – 5 stories)

  • More commercial flexibility, but residential allowed upstairs. May support projects where retail or amenity is desired at ground level.
  • Good where commercial frontage is desired.

What About 3-Stories?

While these 5-story single-stair buildings are intended for zoning districts that allow 5-story construction, they can be even more advantageous at 3-stories. These simpler buildings avoid the need for an elevator and carry fewer life-safety cost premiums, making them generally easier to entitle and pencil even if you’re only building 11-12 units. Additionally, there are more potential properties with this zoning that are in the sweet spot between 6,000 and 8,000 SF. Here are some key zoning districts you might want to consider:

G-MU-3 (General Urban – Multi-Unit, 3 stories)

  • Flexible multi-unit forms, strong match for small footprints and walk-up layouts.

U-RX-3 (Urban – Residential Mixed-Use, 3 stories)

  • Urban context, supports residential with some mixed-use options; good along neighborhood corridors without heavy “Main Street” frontage rules.

G-RX-3 (General Urban – Residential Mixed-Use, 3 stories)

  • Similar intensity to G-MU-3 with additional mixed-use flexibility.

Design Insights for Single-Stair Housing

This new building type is more than a new way to build housing; 5-story single-stair apartments offer a new way to envision living that has the potential to fundamentally change housing in Denver.

  • Slim, efficient footprints with expressive massing
  • Mass timber and modular systems enabling rapid, sustainable construction
  • Activated ground floors with stoops, retail, or community uses
  • Atrium cores that bring light and air into internal circulation spaces

These designs reinforce that single-stair buildings need not compromise fire safety or quality of life—they can exceed expectations, if designed intentionally.

KGA is a Leader

As a Denver-based firm that is an expert in residential design with almost 50 years of experience, KGA is perfectly positioned to lead in this emerging market. We are taking the following strategic steps to do our part to bring this new building type to our city:

  1. PROTOTYPE DEVELOPMENT: We’re modeling a series of code-compliant 5-story single-stair building plans for Denver zoning districts, demonstrating modularity, affordability, and beauty. See our prototype designs:
  2. REGULATORY FLUENCY: We are tracking and participating in the code amendment process, ensuring our clients can move quickly once changes are adopted.
  3. DEVELOPER EDUCATION: We’re preparing targeted outreach to inform developers of how this typology opens up new, profitable development models for narrow or difficult urban parcels.
  4. POLICY COLLABORATION: Members of the KGA team have been integrally involved in the effort to bring 5-story single-stair housing to Denver since the beginning. We gave testimony to the Colorado Legislature in support of the statewide bill and are actively engaged with city building officials to help craft code amendments that work.

Looking Ahead

Denver’s housing future will be shaped by how well we leverage new regulatory opportunities like the single-stair residential model. As a firm that is passionate about affordable housing with deep design expertise and a proactive, code-forward approach, KGA is the ideal firm to partner with on delivering smart, safe, and sustainable housing that meets the moment.

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