Denver ADU Builder — 2022 Group Living + No-State-GC + WUI + DORA Trade Stack

If you searched "denver adu builder" any time before February 2022, most of what you found no longer reflects Denver's zoning reality. The 2022 Group Living amendments (Ordinance 20-1165, phased in through 2022) rewrote single-family zoning to allow ADUs on a far wider set of parcels. And the underlying licensing architecture in Colorado is almost the opposite of what homeowners arriving from California, New York, or Florida expect. Colorado has no statewide general contractor license. Prime contractor licensing is municipal, and in Denver the city issues a Class A through Class D Contractor License under Article III of the Denver Building Code. The trades — electrical and plumbing — are licensed at the state level through the Colorado Department of Regulatory Agencies (DORA), but DORA does not license general contractors at all. Angi sends your info to twelve strangers. Baily sends it to one Denver-licensed contractor with DORA-verified sub-trades. One vetted builder. Not a lead-broker auction.

What the 2022 Group Living amendments actually changed

Before Group Living, a Denver homeowner who wanted an ADU faced a patchwork of zoning-specific allowances that ruled out most of the city. ADUs were permitted in only a narrow slice of single-family zone districts, often required a public-hearing zoning review that added six to twelve months, and the city issued fewer than 100 new ADU permits in most years through 2019.

Ordinance 20-1165 did three things. First, it expanded the list of single-family zone districts where an ADU is allowed by-right to include a substantially larger share of the E-SU, U-SU, S-SU, and similar single-unit districts. Second, it standardized ADU form standards — height, setback, floor-area ratio, lot coverage — into a cleaner chart. Third, it rewrote the definition of "household" to allow up to five unrelated adults in a primary dwelling (separate from ADU reform, but bundled in the same package).

ADU permit intake at Denver Community Planning & Development (CPD) roughly doubled from 2022 to 2024, concentrated in Berkeley, Sloan's Lake, Park Hill, and Virginia Village — neighborhoods with pre-war housing stock and alley-loaded garages that can host a detached ADU or garage conversion.

Caveats. Owner-occupancy tract overlays still apply in a handful of neighborhoods and were under fresh Council review as of early 2025 — a map check on your specific parcel matters. Historic Districts — Curtis Park, Potter Highlands, Country Club — route through the Denver Landmark Preservation Commission. And the Wildland-Urban Interface (WUI) overlay applies to a meaningful share of foothill-adjacent parcels where Chapter 7A standards add cost most homeowners do not anticipate.

Colorado has no state GC license — Denver municipal tiers + DORA trades

Colorado has no statewide general contractor license. There is no equivalent of California's CSLB, Florida's DBPR, or Washington's L&I at the state level. GC licensing in Colorado is handled exclusively at the municipal level, and rules vary city to city. Denver operates its own regime under Article III of the Denver Building Code. Aurora, Lakewood, Arvada, and Wheat Ridge all operate separate regimes. A Denver Class B license does not carry to Aurora.

What Colorado does license at the state level is the trades — specifically electrical and plumbing — through DORA. The Colorado State Electrical Board inside DORA issues Residential Wireman, Journeyman, and Master Electrician licenses. The Colorado State Plumbing Board inside DORA issues Apprentice, Residential, Journeyman, and Master Plumber licenses. DORA does not license general contractors. If someone tells you they are "DORA-licensed" as a general contractor, that is either a misunderstanding or a misrepresentation. The prime carries a Denver-municipal license. The electrical sub carries DORA Electrical Board credentials. The plumbing sub carries DORA Plumbing Board credentials. HVAC in Denver is regulated through the city's mechanical permitting framework, not DORA.

The verification burden shifts in a specific pattern: you cannot vet a Denver GC through a state database because no such database exists. You can only vet them through Denver Building & Zoning's contractor-license lookup, Denver Court records, and the Colorado Secretary of State entity lookup. The trades you can vet through DORA directly. The prime you cannot.

Denver Class A/B/C/D contractor tiers by project value

Denver's Contractor License is tiered — the class you need depends on the construction value of the project you are signing. A $180,000 detached ADU and a $350,000 high-finish detached ADU may require different contractor classes depending on how Denver Building & Zoning scopes the construction value.

Class A. Highest-tier residential license. Any residential project value, including the largest custom homes and high-value ADUs.

Class B. Residential construction up to a specified project-value cap. Most Denver ADU builds fall under the Class B ceiling, making it the most common credential on your candidate pool — ADU new-builds, garage conversions, basement conversions, and remodels in the $100K to $500K range.

Class C. Smaller-scope work — kitchen and bath remodels, smaller additions, and ADUs at the lowest end of the cost curve. A Class C holder may not have the class required for a $300,000 detached ADU.

Class D. Single-trade or single-room remodels and minor repairs. Almost never the correct license for an ADU.

What to check on your specific builder candidate: (a) the exact class on their current Denver Contractor License; (b) whether that class covers the construction value Building & Zoning will assign to your project at permit submittal; (c) whether the license is active and not in a suspended or probationary status. Denver publishes current class thresholds and license-status data through its contractor-license lookup.

DORA Electrician + Plumber license verification

The most important sub-trade verification on a Denver ADU is the DORA licenses on the actual workers — not just the prime. Colorado statutes (consolidated under DORA's Division of Professions and Occupations) require that all electrical work be performed by or under direct supervision of a state-licensed electrician, and all plumbing work by or under direct supervision of a state-licensed plumber. The DORA license lookup at dora.colorado.gov makes this a 30-second task — enter a license number or name and it returns license type, status, and issuance date.

What most homeowners miss: Colorado's mechanics' lien statute (Title 38, Article 22) gives any unpaid subcontractor a direct lien right against the homeowner's property, even if the homeowner paid the prime in full. If your prime pays an unlicensed electrical sub in cash and stiffs them, that sub can still file a lien against your home. The practical defense: (a) verify DORA licenses on every electrical and plumbing worker; (b) require your prime to provide lien waivers signed by every sub at each draw; (c) insist on a final lien waiver covering all subs before final payment. Baily's Denver network only includes primes who follow this protocol as SOP.

Denver CPD + Building & Zoning dual permit path

Denver ADU permits route through two parallel regulatory bodies: Denver Community Planning & Development (CPD) for zoning, and Denver Building & Zoning for building code, structural, MEP, and energy. Dual-path — different from the single-window portals homeowners from California or Texas expect.

CPD zoning review answers: is the proposed ADU allowed on this parcel, at this size, at this location? Looks at zone district (E-SU-D, U-SU-B, S-SU-I, etc.), applies 2022 Group Living form standards, checks overlays — Historic Districts, WUI, Airport Influence Zone, Design Overlay Districts. Typical timeline 4 to 6 weeks.

Building & Zoning plan review answers: does the construction meet the Denver-adopted 2021 IRC with amendments, the Denver Green Code, the 2021 IECC for CZ 5B, and the structural, MEP, and accessibility provisions of the Denver Building Code? Multi-discipline — structural, mechanical, electrical, plumbing, energy, fire — in parallel. Typical 6 to 10 weeks.

The two reviews run in parallel, not sequentially. Total permit timeline from complete submittal to issued permit is 8 to 14 weeks on a clean project. Add 4 to 8 weeks for Landmark Preservation Commission on Historic District parcels. Add 2 to 6 weeks for WUI overlay review. The most common overrun: a first submittal that fails either review on a preventable issue, costing a full review cycle an experienced builder would have pre-empted.

Altitude + 2021 IECC CZ 5B thermal envelope + radon-resistant construction

Denver sits at 5,280 feet and the Front Range climate puts the city in 2021 IECC Climate Zone 5B — cold-dry. Denver has adopted the 2021 IECC with local amendments that push certain envelope assemblies tighter than the base code.

Wall insulation. R-20 cavity plus R-5 continuous, or R-13 cavity plus R-10 continuous. Tighter than most coastal or southern markets — roughly $3,500 to $7,000 more than a code-minimum assembly in Climate Zone 3 or 4.

Ceiling insulation. R-49 in vented attics, R-38 plus continuous in certain unvented assemblies.

Windows and air sealing. U-factor 0.30 or better. Mandatory blower-door test at substantial completion, target 3.0 ACH50 or better. Pass/fail — an ADU that fails blower-door does not receive Certificate of Occupancy until air-sealing is corrected.

Radon-resistant new construction. Denver is a high-radon zone. The Denver Green Code and Denver's amendments to the IRC require radon-resistant new construction on all new residential structures, including ADUs. Passive sub-slab soil-gas system — 4 inches of gravel, gas-permeable membrane, 3-inch vertical pipe from sub-slab to roof, electrical rough-in for a future active fan. Cost $800 to $1,800 on a detached ADU. Not optional. Basement conversions are the highest-risk radon scenarios and almost always require active mitigation after post-construction testing.

Altitude also changes HVAC sizing — Manual J loads at 5,280 feet differ from the same envelope at sea level. A Denver HVAC contractor without elevation experience will consistently undersize or mis-duct. Baily screens for this when matching the mechanical sub.

WUI Chapter 7A — the foothill properties where it applies

Denver's WUI overlay is defined under Denver Building Code Chapter 7A, based on the California-originated framework adapted to Colorado Front Range fire conditions. The overlay applies to roughly 8% of Denver County — concentrated in the far western edge near the foothills. The 8% figure understates the importance, because WUI-mapped parcels tend to cluster in high-value neighborhoods where ADU economics are strong.

Chapter 7A imposes three categories of ignition-resistance requirements:

Class A roofing. Roof must meet ASTM E108 Class A fire rating — asphalt composition shingle over compliant underlayment, concrete or clay tile, metal, or other rated assemblies. Wood shake effectively prohibited.

Ember-resistant venting. All attic and crawl-space vents must be ember-resistant — 1/8-inch mesh or WUI-listed vent assemblies. Modest cost delta, but installation quality matters.

Ignition-resistant siding. Exterior walls facing the unmitigated fuel zone must be non-combustible or ignition-resistant — stucco, fiber-cement, brick, masonry, or rated assemblies. Largest WUI cost line, typically $8,000 to $20,000 on a detached ADU versus a standard wood-clad envelope.

Chapter 7A also adds defensible-space requirements that may interact with existing mature trees and require a Denver Forestry consultation. If your ADU is WUI-mapped, a builder who has closed WUI ADUs before is non-negotiable. The common failure mode: a builder who bids a standard envelope, discovers the WUI overlay at permit submittal, and comes back with a change order that was never budgeted.

Historic overlays — Curtis Park, Potter Highlands, Country Club

Denver has more than 50 designated Historic Districts. The ones most relevant to ADU builds include Curtis Park (one of Denver's oldest residential neighborhoods), Potter Highlands (north Highlands, pre-1910 housing stock), and Country Club (early 20th-century estate lots south of Cheesman Park). A parcel inside any Historic District is subject to design review by the Denver Landmark Preservation Commission, which evaluates any exterior change — new detached ADU, garage conversion, or exterior modification to a historic garage — against district-specific design standards.

Your ADU design cannot just meet zoning and building code. It has to satisfy the Historic District's design guidelines — materials, roof pitch, window proportions, siding patterns, placement on the lot. Landmark Preservation review adds 6 to 12 weeks on top of standard CPD and Building & Zoning review, and a rejected design can add a full rebuild cycle. Baily's Denver match on Historic District parcels specifically requires at least one closed ADU inside a Denver Historic District in the builder's portfolio.

Utility tap fees — Denver Water + Wastewater SDC

Two utility costs on a Denver ADU are separate from your building permit fees and are paid directly to utility providers. They catch homeowners off-guard because they are commonly quoted late in permitting.

Denver Water System Development Charge (SDC). Charged on any new water service connection. For an ADU, the SDC depends on whether the ADU shares the primary residence's water service (lower SDC) or requires a new dedicated meter (higher SDC). Shared service typically $2,000 to $5,000. New dedicated service with a separate meter $5,000 to $12,000.

Denver Wastewater SDC. Separate charge for sewer, paid to Denver Wastewater Management. Typically $2,000 to $6,000 on a shared service and higher on dedicated. Depends on meter size and the fee schedule at tap.

Stack total. Shared service: Denver Water + Wastewater SDCs stack to $4,000 to $11,000. New dedicated ADU service: $8,000 to $18,000. On top of construction cost, on top of permit fees. A line item that should be surfaced in your builder's first proposal — not discovered at permit submittal.

Cost bands: $45K to $350K by ADU type

All-in turnkey pricing including permits, design, site work, utility tap fees, finishes, and required radon-resistant construction. Assumes 2021 IECC CZ 5B envelope compliance. Does not assume WUI upgrades — add $8,000 to $25,000 if your parcel is WUI-mapped.

Detached new-build ADU: $180,000 to $350,000. Low end: 600 to 700 square foot one-bedroom on a flat lot with a short utility run and simple gable roof. High end: 900 to 1,000 square foot two-bedroom with architect-designed envelope, high-end finishes, and a longer utility-extension trench.

Garage conversion ADU: $85,000 to $165,000. Converting an existing detached alley-loaded garage. Low end: proper slab, stub-outs within 20 feet, pitched roof that can host a compliant envelope without major reframing. High end: full gut — new roof, new insulation, new MEP, new cladding, plus legalization if the garage was previously unpermitted.

Basement conversion ADU: $45,000 to $110,000. Converting an existing basement into a conforming ADU. Low end: walk-out basement with egress windows, bathroom rough-in, adequate ceiling height (7 feet min per Denver-adopted IRC). High end: full dig-down to add ceiling height, new egress-window well, active radon mitigation, and a new exterior entry with fire separation from the primary.

Cost drivers inside each band: foundation type, utility extension distance (every 20 linear feet of new sewer is $3,500 to $6,500), kitchen and bath finish level, HVAC choice (mini-split heat pump vs ducted furnace + A/C), and whether post-construction radon testing triggers active mitigation ($1,500 to $3,500 add).

Permit timeline + what Baily verifies before any Denver match

Typical clean-project timeline. CPD zoning review 4 to 6 weeks + Building & Zoning plan review 6 to 10 weeks, in rough parallel, yielding a permit in 8 to 14 weeks from complete submittal. Add 4 to 8 weeks for Landmark Preservation Commission. Add 2 to 6 weeks for WUI Chapter 7A review.

Construction after permit. 4 to 7 months for a detached new-build, 3 to 5 months for a garage conversion, 2 to 4 months for a basement conversion. Total elapsed time from signed design contract to Certificate of Occupancy is realistically 7 to 14 months.

Baily's pre-match verification:

1. Denver Contractor License — active, correct class (A/B/C/D) for project value, no suspensions.
2. DORA Electrical Board license on the electrical sub — Master or Journeyman.
3. DORA Plumbing Board license on the plumbing sub — Master or Journeyman.
4. $1M general liability COI — pulled directly from the carrier.
5. Colorado workers' compensation — verified through carrier, cross-checked with the Division of Workers' Compensation.
6. No open mechanics' liens — Denver County Clerk and Recorder search under Colorado Revised Statutes Title 38, Article 22.
7. Three-plus years continuous operating history — Colorado Secretary of State entity lookup.
8. Portfolio verification — at least five Denver ADUs closed with Certificate of Occupancy since January 2022; for Historic Districts, at least one closed ADU inside a Denver Historic District; for WUI parcels, at least one closed WUI-compliant ADU.

If a builder fails any of the eight, Baily does not introduce them. One vetted builder. Not twelve strangers chasing your phone number in a lead-broker auction.

Frequently asked questions

Does Colorado require a general contractor license for ADU construction?

No — Colorado is a no-statewide-GC-license state. Contractor licensing is municipal. In Denver specifically, any contractor doing work over $2,000 needs a Denver-issued Contractor License (Class A, B, C, or D depending on project value) from Denver Building & Zoning. Colorado DORA licenses the TRADES — electricians and plumbers need state licenses — but the general contractor holding the prime is Denver-municipal only.

What does DORA actually license in Colorado?

DORA — the Colorado Department of Regulatory Agencies — licenses the building trades, not general contractors. The Electrical Board inside DORA licenses Residential Wiremen, Journeyman, and Master Electricians. The Plumbing Board inside DORA licenses Apprentice, Residential, Journeyman, and Master Plumbers. If someone tells you they hold a "DORA general contractor license," that is a misunderstanding — DORA does not license GCs. The prime on your Denver ADU carries a Denver-municipal Contractor License. The electrical sub carries DORA Electrical Board credentials. The plumbing sub carries DORA Plumbing Board credentials. HVAC is licensed through Denver, not DORA.

How long does a Denver ADU permit take through CPD and Building & Zoning?

Plan on 8 to 14 weeks from complete submittal to issued permit for a clean ADU on a non-Historic, non-WUI parcel — CPD zoning review 4 to 6 weeks and Building & Zoning plan review 6 to 10 weeks, in rough parallel. Add 4 to 8 weeks if your parcel is inside a Denver Historic District and routes through the Landmark Preservation Commission. Add 2 to 6 weeks if WUI Chapter 7A review applies. Construction runs 4 to 7 months for a detached new-build, 3 to 5 months for a garage conversion, and 2 to 4 months for a basement conversion, so total elapsed time from signed design contract to Certificate of Occupancy is typically 7 to 14 months.

Is radon-resistant construction actually required on Denver ADUs?

Yes. The Denver Green Code and Denver's IRC amendments require radon-resistant new construction on all new residential structures, including ADUs. Passive sub-slab soil-gas system — 4 inches of gravel, gas-permeable membrane, 3-inch vertical pipe from sub-slab to roof, electrical rough-in for a future active fan. Typically $800 to $1,800 on a detached ADU. Basement conversions carry the highest radon risk and frequently require active mitigation (in-line fan in the vent pipe) after post-construction testing. Not optional — baseline code.

What's the cost difference between detached, garage conversion, and basement conversion in Denver?

At Denver 2026 pricing, a detached new-build ADU runs $180K to $350K, a garage conversion $85K to $165K, and a basement conversion $45K to $110K. The deltas come from three drivers. First, foundation and envelope — a new-build needs a fresh foundation, full envelope, and new roof ($70K to $120K on its own). A garage conversion reuses the slab and most of the envelope. A basement conversion reuses the entire primary structure. Second, utility extension — a detached ADU frequently needs 30 to 60 feet of new sewer, water, and electrical trench ($12K to $25K). A garage conversion usually has stub-outs within a few feet. A basement conversion taps off existing interior MEP. Third, MEP scope — a new-build runs all new rough-ins; conversions reuse substantial portions. Tradeoff: flexibility (detached) versus economics (basement).

Sources and citations

1. Denver City Council Ordinance 20-1165 (Group Living amendments): https://www.denvergov.org/Government/Agencies-Departments-Offices/Agencies-Departments-Offices-Directory/Community-Planning-and-Development/Denver-Zoning-Code/Text-Amendments/Group-Living
2. Denver Community Planning & Development — ADU resources and zoning lookup: https://www.denvergov.org/Government/Agencies-Departments-Offices/Agencies-Departments-Offices-Directory/Community-Planning-and-Development/Zoning/Accessory-Dwelling-Units
3. Denver Building & Zoning — contractor license classes and lookup: https://www.denvergov.org/Government/Agencies-Departments-Offices/Agencies-Departments-Offices-Directory/Community-Planning-and-Development/Permits/Contractor-Licensing
4. Colorado DORA — Electrical Board (license lookup, types, statutes): https://dpo.colorado.gov/Electrical
5. Colorado DORA — Plumbing Board (license lookup, types, statutes): https://dpo.colorado.gov/Plumbing
6. Colorado Revised Statutes Title 38, Article 22 — Mechanics' Liens: https://leg.colorado.gov/sites/default/files/images/olls/crs2022-title-38.pdf
7. Denver Building Code Chapter 7A — Wildland-Urban Interface: https://www.denvergov.org/Government/Agencies-Departments-Offices/Agencies-Departments-Offices-Directory/Community-Planning-and-Development/Building-Codes-Policies-and-Guides
8. Denver Water — System Development Charge schedule: https://www.denverwater.org/customer-service/rates/fees/system-development-charges
9. 2021 International Energy Conservation Code (CZ 5B envelope, blower-door, radon-resistant): https://codes.iccsafe.org/content/IECC2021P1
10. Colorado Division of Workers' Compensation — coverage verification: https://cdle.colorado.gov/dwc