If you own a home in Denver and have ever looked at your backyard, garage, or basement and thought “there has to be more I can do with this space,” you’re not alone — and the answer in 2026 is a clearer “yes” than it has ever been. Thanks to a citywide ordinance passed in late 2024 and a state law that went into effect in mid-2025, Denver homeowners now have broader rights to build an accessory dwelling unit than at any point in the city’s history.
But “you can build one” and “you can build one easily” are two very different sentences. Zoning details, utility connections, lot dimensions, and permit timelines still vary block by block. This guide walks through what accessory dwelling units are actually allowed in Denver right now, what it costs, how long it takes, and what you need to know before you break ground.
What Is an Accessory Dwelling Unit?
An accessory dwelling unit — commonly shortened to ADU — is a self-contained secondary home built on the same lot as a primary single-family residence. It has its own kitchen, bathroom, sleeping area, and entrance, and it functions independently of the main house even though the two share a property.
ADUs go by a lot of names. You’ll hear them called granny flats, mother-in-law suites, casitas, carriage houses, garden cottages, and backyard homes. Denver’s zoning code recognizes three primary configurations:
- Detached ADUs — standalone structures, usually built in the rear yard
- Attached ADUs — units that share a wall with the main home, like a converted side addition
- Internal ADUs — units carved out within the existing home, such as a basement apartment
For a fuller breakdown of the accessory dwelling unit definition, types, and how they differ from other secondary housing options, the what is an accessory dwelling unit overview is a good starting point. And if you’ve been wondering how an ADU differs from a tiny home — they’re related but legally distinct — that comparison is worth understanding before you commit to a build type.
The Short Answer: Yes, You Can Likely Build a Denver Accessory Dwelling Unit
In November 2024, Denver City Council passed File 24-1302 and a companion package of bills that allowed ADUs in all residential zone districts citywide. The mayor signed the measure on November 21, 2024, and it took effect in December 2024. Before that change, only about 36% of Denver’s land area was zoned for ADUs. After it, roughly 70% of the city’s residential land became eligible.
That citywide allowance was reinforced at the state level by Colorado House Bill 24-1152, signed by Governor Polis in May 2024. The law required every Colorado municipality with more than 1,000 residents that’s part of a metropolitan planning organization to allow at least one ADU on any lot zoned for a single-family detached home — and to approve those applications administratively, without a public hearing — by June 30, 2025.
The practical effect: if you own a single-family home in Denver, you almost certainly live in a zone district that allows an ADU. There are still exceptions (some historic overlays, certain lot configurations, HOA covenants that predate the changes), but the days of needing a multi-month rezoning hearing for a backyard cottage are mostly over.
How Many ADUs Has Denver Actually Permitted?
Denver began tracking ADU permits in 2016. As of the late 2024 council vote, the city had issued 548 ADU permits, of which 394 had been completed. In 2024 alone, 112 ADU residential construction permits were opened. Those numbers were already trending upward before the citywide ordinance, and local builders have reported a noticeable bump in inquiries since the rule change.
Denver’s ADU Zoning Rules: The Details That Still Matter
Citywide eligibility doesn’t mean a free-for-all. Denver’s zoning code still governs how big your ADU can be, where it sits on the lot, and how tall it can rise. Here are the standards that apply to most single-unit residential lots:
Size limits (detached ADUs):
- Lot under 6,000 sq ft → 650 sq ft maximum footprint
- Lot 6,000–7,000 sq ft → 864 sq ft maximum footprint
- Lot over 7,000 sq ft → 1,000 sq ft maximum footprint
For 1.5-story ADU forms, the upper-level habitable space is capped at 75% of the floor area below. So an 864 sq ft footprint allows up to 648 sq ft of living space on the second level.
Placement:
- The ADU must sit in the rear 35% of the zone lot
- A 15-foot separation between the primary house and the ADU is required to qualify for the 50% lot coverage exemption
- The uninterrupted length of the ADU structure cannot exceed 36 feet
Setbacks:
- One-story ADUs must be set back at least 5 feet from rear property lines
- Two-story units may require 12 to 20 feet, depending on zone
- Side setbacks match those of the primary dwelling
Owner occupancy: Denver has historically required that the property owner live in either the primary home or the ADU. Recent state-level changes have begun rolling back owner-occupancy requirements in many Colorado jurisdictions, so confirm the current rule with Community Planning and Development before assuming anything.
Roof decks: Generally not permitted in the rear 35% of the lot, which is exactly where your ADU has to sit. A few districts (such as the General Urban “G” zone) make exceptions, but most lots cannot have a rooftop deck on the ADU.
To verify what applies to your specific address, Denver’s online zoning map and the city’s Accessory Dwelling Units map are the definitive starting points. The zone designation that ends in “1” (for example, E-SU-B1) permits ADUs by right; designations ending in “2” allow them on certain corner lots only.
What Does It Cost to Build an ADU in Denver?
This is the question that derails the most projects. Denver ADU construction is more expensive than most homeowners expect, primarily because every ADU — regardless of size — needs the same core systems: a kitchen, a bathroom, electrical service, water and sewer connections, insulation, and permits. Those fixed costs don’t shrink proportionally with square footage.
Here’s what the Denver market looks like in 2026:
| ADU Type | Typical Cost Range | Notes |
|---|---|---|
| Garage conversion | $100,000–$170,000 | Lower if existing slab and structure are sound |
| Internal/basement ADU | $130,000–$250,000 | Faster permitting; depends on existing layout |
| Attached ADU | $280,000–$350,000 | Shares walls and some utilities with the main home |
| Detached ADU (600–900 sq ft) | $230,000–$450,000 | New foundation, separate utility taps |
| Premium detached (1,000+ sq ft) | $400,000–$550,000+ | High-end finishes, custom design |
Per-square-foot pricing in Denver typically runs $400 to $550 per finished square foot for new detached construction, with garage conversions and basement build-outs coming in lower. Detailed cost estimates for various ADU sizes and configurations are broken down further in the cost to build an accessory dwelling unit guide.
Hidden costs to budget for:
- Denver Water System Development Charges (SDCs) — meter size and demand drive these fees, and they can shift your budget more than most homeowners anticipate
- DOTI Sewer Use and Drainage Permit (SUDP) — older clay lateral lines often need replacement to meet current standards
- Utility upgrades — overhead lines in alleys, transformer spacing, and main service capacity can all trigger additional work
- Alley conditions — sloped, flooded, or aging alleys may require grading or paving
- Soil and foundation work — Denver’s expansive clay soils sometimes require engineered foundations
- Asbestos or lead remediation — common in older garage conversions
- Plan and engineering fees — typically 10–15% of total project cost
- Permit fees — generally $1,350 to $9,000 depending on scope
A 10–15% contingency on top of your hard construction budget is standard advice from experienced Denver builders. Little Home Builder’s ADU cost calculator can give you a tailored estimate based on your lot, size goals, and finish level, alongside rental ROI and added-value tools.
Denver ADU Permit Timeline: What to Expect
Permitting is where ADU projects most often stall, and it’s worth setting expectations early. In April 2025, Mayor Mike Johnston signed Executive Order 151, creating the Denver Permitting Office (DPO). The DPO consolidated review functions and set a 180-day target review period for most residential permits, with dedicated “project champions” assigned to applicants and a two-business-day response goal for inquiries.
That’s the policy goal. The on-the-ground reality is still catching up. City data from late 2025 showed the actual average time from submittal to application approval running closer to 244 days for large residential projects, well above the 180-day target. The DPO is making progress on backlog reduction — pre-DPO timelines had stretched past 300 days — but homeowners should plan for several months of review, not several weeks.
A realistic ADU project timeline from feasibility to certificate of occupancy:
- Feasibility and design — 4 to 12 weeks
- Plan submittal and review — 3 to 8+ months (multiple review cycles common)
- Construction — 4 to 8 months for detached ADUs; 2 to 5 months for conversions
- Final inspections and CO — 2 to 4 weeks
Total: 9 to 18 months from first sketch to move-in day for most projects.
Reviews you’ll go through include zoning, building code, fire (required for all ADUs), Denver Water (taps and SDCs), DOTI (SUDP for sewer and drainage), and — if you’re in a historic district — Landmark Preservation. The step-by-step guide to getting an ADU permit in Denver walks through each stage in detail, including the documents you’ll need at each step.
Choosing Your ADU Type: Three Paths That Work in Denver
The right ADU for your property depends on lot dimensions, budget, and what you want the unit to do.
Garage conversions are the lowest-cost path into ADU ownership for most Denver homeowners. If you already have a detached garage with a sound slab and structure, converting it into living space avoids new foundation work and often preserves the existing utility runs. That said, many older Denver garages need a new insulated foundation, new electrical service, plumbing, and full code-compliant insulation — so “cheap” is relative. The ADU garage conversion guide and the companion piece on garage conversions as an affordable ADU option cover the structural and design considerations in detail.
Backyard cottages — detached, purpose-built ADUs — are the most flexible option and typically the most valuable on resale. You design the layout from scratch, position it to maximize privacy from the main house, and end up with what’s effectively a small home rather than a renovated outbuilding. The trade-off is cost and timeline. A backyard cottage is a ground-up build with all the design, foundation, and utility work that implies. The guide to backyard cottages explains why this format has become Denver’s most popular ADU type for homeowners with the budget to support it.
Internal and basement ADUs are the fastest path to permitted occupancy because they involve no new exterior structure. HUD has noted that internal ADUs often see faster approval timelines in jurisdictions like Denver. The catch is egress: any basement ADU must have compliant emergency egress windows and a radon mitigation system under Colorado building standards.
If you’re trying to decide between formats, looking at examples helps. Little Home Builder’s project gallery shows completed Denver-area ADUs across all three types, and the ADU plans library includes pre-designed accessory dwelling unit plans that have already cleared Denver’s design standards — a meaningful time-saver if you’re trying to avoid custom architecture fees.
Can You Rent Out a Denver ADU?
Yes — with some conditions.
Long-term rentals (30+ days): Permitted on any compliant ADU. You’ll need to obtain a long-term rental license from the city, and the unit must have its own assigned address and pass all inspections before it can be occupied.
Short-term rentals (under 30 days): Allowed, but only under specific conditions. You must live in either the primary dwelling or the ADU as your primary residence, and you can only operate the short-term rental in the unit that is not your primary residence. In practice: live in the main house and STR the ADU is fine. Live in the ADU and STR the main house is also fine. Live in the ADU and STR the ADU — not allowed.
Short-term rentals require a separate STR license through Denver’s Department of Excise and Licenses, plus compliance with city tax provisions.
For homeowners weighing whether to build for family use or rental income, the breakdown of how ADUs provide extra income opportunities for Denver homeowners covers typical Denver rental rates, ROI math, and the tax implications worth knowing before you sign a lease.
Financing Your Denver ADU
Most Denver homeowners finance an ADU through one of four channels: a cash-out refinance, a home equity line of credit (HELOC), a home equity loan, or a construction loan. Each has trade-offs around rate, payment structure, and how the lender treats the ADU’s projected rental income.
Colorado House Bill 24-1152 also set the stage for new state-supported financing programs. The legislature appropriated up to $8 million for low- and moderate-income homeowner ADU loans and down-payment assistance through the Colorado Housing and Finance Authority (CHFA), available through local lenders in jurisdictions certified as ADU-supportive.
Little Home Builder’s ADU financing page walks through the lending paths available in Denver and which lenders have experience underwriting ADU projects specifically.
HOAs, Historic Districts, and the Edge Cases
A few situations still complicate ADU projects even after the citywide rule change:
- HOA covenants. Colorado’s 2024 law restricts many HOA bans on ADUs, but private covenants can still impose design controls, size limits, and approval processes. Review your HOA documents before you spend a dollar on design.
- Historic districts and landmark properties. Landmark Preservation review is required before a building permit can be issued. This adds time and design constraints but doesn’t prohibit ADUs.
- Lot constraints. Bulk planes, setbacks, and the rear 35% rule can disqualify some narrow or oddly shaped lots even in eligible zones. A site-specific zoning analysis early in the process saves money later.
- Setback conflicts. Denver’s required setbacks in some suburban-context neighborhoods (10 feet) exceed the state’s 5-foot mandate. The city has signaled willingness to defend its standards, and the matter may continue to evolve through future legislation.
Should You Build a Denver Accessory Dwelling Unit?
If you have a lot that supports one, the math often works — especially when you account for long-term rental income, increased property value, and the flexibility of having a second living space for family. A rough rule of thumb used by local builders: a completed ADU adds roughly 20–30% to a primary home’s market value, though that number swings based on neighborhood and finish level.
The homeowners who succeed with ADU projects tend to share three habits: they confirm zoning and utility capacity before they fall in love with a design, they budget realistic contingencies (10–15% is the floor), and they work with builders who have actually completed Denver projects and understand the city’s review process.
If you’re ready to figure out whether your lot can support an ADU, the team at Little Home Builder specializes in accessory dwelling units throughout the Denver metro area. You can review the ADU plans we build, run the numbers on the ADU calculators, or check the FAQ for answers to the questions Denver homeowners ask most. You can also learn more about our company and how we help homeowners take a Denver ADU from feasibility through certificate of occupancy.
Denver has spent a decade reshaping its zoning code to make accessory dwelling units more accessible. In 2026, the path is clearer than it’s ever been — but the details still matter. The sooner you start checking them, the sooner you can break ground on a backyard that does more than hold a lawn.
