How to Choose an ADU Contractor in Colorado (Questions to Ask)
How to hire an ADU contractor in Colorado, the questions to ask, the red flags to avoid, how licensing works here, and modular versus site-built compared.
Denver’s real rules, taxes and rents — read from the codified ordinance, every figure sourced and dated. Here: rents floored at $1,754/mo. Run your own numbers below, free.
Read from the Denver Zoning Code itself — the operative legal text, not a website summary. Denver is an HB24-1152 subject jurisdiction: since June 30, 2025, Colorado law guarantees one ADU by right on any lot with a single-family home here.
| Maximum ADU size | Single-unit (SU) zones: 864 sq ft on lots up to 7,000 sq ft, 1,000 sq ft on larger lots — attached or detached. Other residential zones: attached ADUs up to 75% of the main home or 864 sq ft, whichever is greater; detached ADUs follow the building-footprint cap — 864 sq ft on lots up to 7,000 sq ft, 1,000 sq ft above that (Urban Neighborhood Context zones)verified September 2026Denver Zoning Code Art. 11 §11.8.2.1.B.2the ordinance text"The Gross Floor Area (GFA) of an Accessory Dwelling Unit use shall not exceed the limits as stated in the following table..." Table: "Single Unit Dwelling Use - All SU Zone Districts where ADU use is permitted with limitations | Attached or Detached | 7,000 sf or less -> 864 sf ... Greater than 7,000 sf -> 1,000 sf"; "Single Unit Dwelling Use - All Zone Districts Except SU Zone Districts... | Attached | Not applicable | 75% of Primary Use GFA or 864 sf, whichever is greater"; "Single Unit, Two Unit and Multi Unit Dwelling Uses - All Zone Districts Except SU Zone Districts... | Detached | Not applicable | Not applicable". Building-form table (Art.5 5.3.4.5.A): "Building Footprint (max) ... All U-SU By Zone Lot Area: 7,000 sf or Less -> 864 sf per unit; Greater than 7,000 sf -> 1,000 sf per unit ... All U-TU, RH, RX, MX, MS -> 1,000 sf per unit". |
| Size relative to the main house | 75% of the main home's floor area, or 864 sq ft, whichever is greater — attached ADUs outside SU zones; SU-zone and detached ADUs use the flat caps aboveverified September 2026Denver Zoning Code Art. 11 §11.8.2.1.B.2the ordinance text"Single Unit Dwelling Use - All Zone Districts Except SU Zone Districts where ADU use is permitted with limitations | Attached | Not applicable | 75% of Primary Use GFA or 864 sf, whichever is greater" |
| Height limit | 24 ft and two stories for detached ADUs in Urban Neighborhood Context zones, with a side bulk-plane limit (12 ft vertical on lots 40 ft or narrower, 10 ft on wider lots in U-SU/TU zones; 12 ft in U-RH/RX/MX/MS) rising at 45°verified September 2026Denver Zoning Code Art. 5 Div. 5.3the ordinance text"HEIGHT ... A Stories (max) 2 2 ... A Feet (max) 24' 24' ... B Bulk Plane Vertical Height at Side Interior Zone Lot Line: Lots 40' wide or less: 12' / Lots greater than 40' wide: 10' [U-SU,TU] ... 12' [U-RH,RX,MX,MS] ... Bulk Plane Slope from Side Interior Zone Lot Line 45° 45°" |
| Owner occupancy | In SU zones only, and only when you apply: at least one owner must live in the main home at permit application — not an ongoing requirement. Exceptions for Denver Housing Authority properties and for ADUs built together with a new main homeverified September 2026Denver Zoning Code Art. 11 §11.8.2.2the ordinance text"The owner occupancy requirement in this subsection 11.8.2.2.B. shall apply to the establishment of all Accessory Dwelling Unit uses in a SU zone district with the exception of Accessory Dwelling Unit uses accessory to Primary Dwelling Units owned by the Housing Authority of the City and County of Denver (DHA)..."; "At the time a permit application is submitted for an Accessory Dwelling Unit use accessory to an existing Primary Dwelling Unit, at least one owner of the existing Primary Dwelling Unit shall occupy the existing Primary Dwelling Unit as the owner's primary residence, except as provided in Section 11.8.2.2.B.2.b below."; "The owner is not required to occupy a dwelling unit on the property at the time a permit application is submitted when a structure containing an Accessory Dwelling Unit use is being constructed simultaneously with a new Primary Dwelling Unit structure." |
| Short-term rental | Yes, with conditions: only the resident of the main home may operate a short-term rental (in either the home or the ADU); someone living in the ADU may not run an STR in either unit, and only one STR booking may run on the lot at a timeverified September 2026Denver Zoning Code Art. 11 §11.8.10.1the ordinance text"Shall be operated by the person or persons maintaining the Primary Dwelling Unit as their primary residence, or in an Accessory Dwelling Unit on the same Zone Lot as their primary residence." (11.8.10.1.C); "A Short-Term Rental accessory use cannot be operated by a person or persons maintaining their primary residence in an Accessory Dwelling Unit." (11.8.10.1.C.3) |
| Setbacks | Detached ADUs (Urban Neighborhood Context zones): sited in the rear 35% of the lot; side setbacks 3 ft on lots 40 ft or narrower and 5 ft on wider lots (3 ft flat in U-RH/RX/MX/MS); rear setback 5 ft, or 0 ft where an alley abuts and garage doors don't face itverified September 2026Denver Zoning Code Art. 5 Div. 5.3the ordinance text"Location of Structure: Located in the rear 35% of the zone lot depth"; "Side Interior and Side Street (min): Lots 40' wide or less: 3' / Lots greater than 40' wide: 5' [U-SU,TU]; 3' [U-RH,RX,MX,MS]"; "Rear, where Alley (public or private) does not abut a Rear Zone Lot Line (min): 5' / 5'"; "Rear, where Alley (public or private) abuts a Rear Zone Lot Line and garage doors face Alley (min): 5' / 5'"; "Rear, where Alley (public or private) abuts a Rear Zone Lot Line and where garage doors do not face Alley (min): 0' / 0'" |
Source: Denver Zoning Code, Art. 11 Div. 11.8 · ordinance text retrieved 2026-09-09, re-verified September 2026 · open “the ordinance text” under any figure to read the exact sentence it comes from.
Denver’s size cap is conditional rather than a single number: Single-unit (SU) zones: 864 sq ft on lots up to 7,000 sq ft, 1,000 sq ft on larger lots — attached or detached. Other residential zones: attached ADUs up to 75% of the main home or 864 sq ft, whichever is greater; detached ADUs follow the building-footprint cap — 864 sq ft on lots up to 7,000 sq ft, 1,000 sq ft above that (Urban Neighborhood Context zones) — worth reading closely before sizing a unit.
Short-term rental is conditional: Yes, with conditions: only the resident of the main home may operate a short-term rental (in either the home or the ADU); someone living in the ADU may not run an STR in either unit, and only one STR booking may run on the lot at a time.
Property tax runs lighter than most of the state here: 79.602 mills total, about 11% below the median of the Colorado tax areas we track.
What an ADU adds to the tax bill in Denver, and the conservative floor on what it rents for.
Levies: City and County of Denver Assessor's Office — '2025 Abstract of Assessment' / 'General Information: Summary of Levies and Taxes' (Assessor Keith A. Erffmeyer; Mayor Michael Johnston). Rates: Colorado DOLA, TY2026 — the 10% reduction on the first $700,000 of value applies to the local-government portion, once per property. Rents: HUD Fair Market Rents, huduser.gov.
Two ways to build the same unit in Denver. Both figures are all-in — design, permits, foundation, utility connections and installation.
Published Front Range ranges for a comparable one-off build, 2025–26
≈ $2,100–$2,600 / month fully financed
≈ $2,800–$3,500 / month fully financed
Olerra ranges: published all-in project pricing, September 2026 — site preparation, foundation, utility connections and permitting included.
Free and specific to you. Want to go further?
Yes. The Denver Zoning Code permits accessory dwelling units (Art. 11 Div. 11.8), subject to the size, height, setback and use rules quoted above from the ordinance text. Denver is also an HB24-1152 subject jurisdiction, so since June 30, 2025 state law requires one ADU to be allowed on any lot with a single-family home. Zoning district, lot size and setbacks still decide what fits on a specific lot — the free property check confirms yours.
Yes. An ADU is a new dwelling unit, so Denver requires a building permit (plus any zoning or site-plan review the code calls for) before construction starts. Olerra's all-in price includes permitting, and factory-built units are inspected to the same building code as a site-built home.
Per the Denver Zoning Code: Single-unit (SU) zones: 864 sq ft on lots up to 7,000 sq ft, 1,000 sq ft on larger lots — attached or detached. Other residential zones: attached ADUs up to 75% of the main home or 864 sq ft, whichever is greater; detached ADUs follow the building-footprint cap — 864 sq ft on lots up to 7,000 sq ft, 1,000 sq ft above that (Urban Neighborhood Context zones). Both Olerra Flex Flats — the 490 and the 735 — are designed to fit typical Colorado caps; check the rules table above for the exact ordinance text.
It depends: Yes, with conditions: only the resident of the main home may operate a short-term rental (in either the home or the ADU); someone living in the ADU may not run an STR in either unit, and only one STR booking may run on the lot at a time.
Per the ordinance: In SU zones only, and only when you apply: at least one owner must live in the main home at permit application — not an ongoing requirement. Exceptions for Denver Housing Authority properties and for ADUs built together with a new main home.
A one-off site build with a general contractor typically runs about $500,000–$650,000 for a ~490 sq ft unit. Olerra's factory-built Flex Flats run $300,000–$365,000 (490) and $420,000–$465,000 (735) all-in — site preparation, foundation, utility connections and permitting included.
Roughly $554 per year for every $100,000 of value the ADU adds, using the local mill levy split across Colorado's TY2026 school (7.05%) and local-government (6.80%) assessment rates.
Same method, each city’s own ordinance. The Colorado hub lists every city, and the statewide ADU calculator covers any Colorado address.
Guides and real Colorado numbers from our team — a fresh pick every couple of weeks, or search for exactly what you need.
How to hire an ADU contractor in Colorado, the questions to ask, the red flags to avoid, how licensing works here, and modular versus site-built compared.
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Planning departments and journalists are welcome to reference this data.
Olerra ADU Cost Calculator — Denver, CO. Data updated September 9, 2026. https://www.olerra.com/adu-calculator/denver/ <a href="https://www.olerra.com/adu-calculator/denver/">Denver ADU rules & costs</a> Data as of September 9, 2026, the oldest figure on the page.
Planning estimates, not quotes or legal advice. Rules, fees, levies and rents change — confirm with the city and your lender before committing. Rules data: codified ordinance as of September 9, 2026, re-verified September 2026. Olerra pricing: published all-in project ranges, September 2026. Corrections: sales@olerra.com.
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