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.
Fort Collins’s real rules, taxes and rents — read from the codified ordinance, every figure sourced and dated. Here: rents floored at $1,537/mo. Run your own numbers below, free.
Read from the Fort Collins Land Use Code itself — the operative legal text, not a website summary. Fort Collins 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 | Detached: 750 sq ft when the main home is under 1,667 sq ft; otherwise up to 1,000 sq ft or 45% of the home, whichever is less. Converting an existing accessory building: 800 sq ft. Attached: the greater of 750 sq ft or 45% of the home (a basement ADU may use the full floor)verified September 2026Fort Collins Land Use Code Ordinance No. 009the ordinance text"Detached ADU with New construction or without non-habitable space (Rear Lot) | Primary Building ≤1,667 ft2 | 750 ft2 max." / "Primary Building ≥1,667 ft2 | 1,000 ft2 max./ or 45% of primary dwelling unit. (whichever is less)" / "Existing accessory structure* | 800 ft2 max.** *Legal structure upon the adoption of the LUC. **Does not include non-habitable space." / "ADU MAX. FLOOR AREA Attached ADU | Located on a floor level at or above grade | The greater of 750 sf or 45% of primary dwelling unit" / "Located on floor level below grade | The greater of 750 sf or 100% of the floor level" |
| Height limit | No taller than the house on the same lot (UE and RF zones; other residential zones set no separate ADU height)verified September 2026Fort Collins Land Use Code Ordinance No. 009the ordinance textUE district table: "Accessory Dwelling Unit | N/A | N/A | No taller than Detached house on the same lot | Located on the same lot with a detached house". RF district table: "Accessory Dwelling Unit | N/A | N/A | No taller than Detached house on the same lot | Located on the same lot with a detached house". MH district table: "Accessory Dwelling Unit (Detached & Attached) | No taller than Mobile Home on the same lot. | No greater than Mobile Home on the same lot. | Only one (1) ADU on a lot with a Mobile Home." |
| Owner occupancy | No — the former resident-manager requirement was removed in February 2025 (Ordinance 009, 2025)verified September 2026Fort Collins Land Use Code Ordinance No. 009the ordinance textCURRENT text (Ordinance No. 009, 2025, replacing former 4.3.1(B)): "(B) Accessory Dwelling Unit shall be subordinate to a primary dwelling unit. The land underneath the primary structure and the accessory dwelling unit is not divided into separate lots. This does not exclude the ability to create a condominium plat." (no owner-occupancy clause follows). SUPERSEDED prior text (as adopted May 2024, no longer in force): "(1) Accessory dwelling units shall have a resident manager residing on the property in the ADU or primary building, when the owner does not reside on the property. (a) The resident manager shall have one (1) primary residence and shall reside on the property for nine (9) months of the calendar year..." Current codified Building Code Appendix BC's 7 conditions (BC101.2, Municode-codified through Ord. 078-2026) include no owner-occupancy condition. |
| Short-term rental | No for new ADUs — any ADU permitted on or after January 1, 2024 may not be used as a short-term rental; ADUs with an earlier STR license may renew itverified September 2026Fort Collins Land Use Code Ordinance No. 009the ordinance text"(1) Accessory Dwellings Units that apply for a building permit on or after January 1, 2024, shall not be used for a short term rental. Existing short term rental licenses issued before January 1, 2024, may be renewed or a new license after this date may be issued per Section 15-646 of the Code of the City of Fort Collins." Municipal Code definition: "Short term primary rental shall mean a dwelling unit that is a primary residence of which a portion is leased to one (1) party at a time for periods of less than thirty (30) consecutive days. An accessory dwelling unit, as defined in the Land Use Code, that is not a primary residence is eligible to be a short term primary rental and may be licensed as a short term primary rental if it is located on a lot containing a primary residence." |
| Extra parking | None beyond the main house — the former one-space requirement was removed in February 2025verified September 2026Fort Collins Land Use Code Ordinance No. 009the ordinance textSUPERSEDED (pre-Feb-2025) text: "(e) Accessory Dwelling Unit. One (1) additional parking space required." CURRENT (post-Feb-14-2025) replacement text, in full: "(a) Single Unit and Two-Unit. Detached House: there shall be one (1) parking space on lots with greater than forty (40) feet of street frontage or two (2) parking spaces on lots with forty (40) feet or less of street frontage. Duplex and Rowhouse: for each dwelling unit with two (2) or fewer bedrooms there shall be one (1) parking space and two (2) parking spaces for each dwelling unit with three (3) or more bedrooms. Parking of any vehicle in the front yard of a lot on which exists a Detached House or Duplex shall be prohibited..." (no ADU entry appears in this or any subsequent lettered item (b) through (g) of the replacement text). |
| Setbacks | Residential Cluster building type: front 15 ft, interior side 5 ft, street side 15 ft, rear 8 ft, and detached ADUs sit behind the main building; other zones use their general accessory-building setbacksverified September 2026Fort Collins Land Use Code Ordinance No. 009the ordinance text"Setbacks for attached, detached, accessory dwelling unit, and accessory buildings in a Residential Cluster ... Accessory Dwelling Unit | 15' min [Front] | 5' min [Interior Side] | 15' min [Street Side] | 8' min [Rear] ... Detached Accessory | Behind primary building [Front] | 5' min [Interior Side] | 15' min [Street Side] | 8' min [Rear]". MH district: "SETBACKS AND SEPARATION Front Setback* 15' min. ... Rear Setback* 10' min. Distance between Mobile Home and Accessory Dwelling Units 10' min. Side Setback* 10' min. Distance between Accessory Structure 3' min. *Setbacks are from property line." |
Source: Fort Collins Land Use Code, §5-30 · 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.
Fort Collins’s size cap is conditional rather than a single number: Detached: 750 sq ft when the main home is under 1,667 sq ft; otherwise up to 1,000 sq ft or 45% of the home, whichever is less. Converting an existing accessory building: 800 sq ft. Attached: the greater of 750 sq ft or 45% of the home (a basement ADU may use the full floor) — worth reading closely before sizing a unit.
Short-term rental is conditional: No for new ADUs — any ADU permitted on or after January 1, 2024 may not be used as a short-term rental; ADUs with an earlier STR license may renew it.
Parking: None beyond the main house — the former one-space requirement was removed in February 2025.
And Fort Collins is one of only 30 Colorado jurisdictions certified ADU Supportive, which makes residents eligible for CHFA’s state-backed ADU financing — an interest-rate buydown and credit enhancement offered through participating lenders. Most of the Front Range doesn’t have this lever.
What an ADU adds to the tax bill in Fort Collins, and the conservative floor on what it rents for.
Levies: Larimer County Assessor — "Mill Levies by Tax Area and Authority 2025" (cross-checked against "Mill Levy by Tax Area Summary 2025"). 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 Fort Collins. 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 Fort Collins Land Use Code permits accessory dwelling units (§5-30), subject to the size, height, setback and use rules quoted above from the ordinance text. Fort Collins 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 Fort Collins 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 Fort Collins Land Use Code: Detached: 750 sq ft when the main home is under 1,667 sq ft; otherwise up to 1,000 sq ft or 45% of the home, whichever is less. Converting an existing accessory building: 800 sq ft. Attached: the greater of 750 sq ft or 45% of the home (a basement ADU may use the full floor). 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: No for new ADUs — any ADU permitted on or after January 1, 2024 may not be used as a short-term rental; ADUs with an earlier STR license may renew it.
Per the ordinance: No — the former resident-manager requirement was removed in February 2025 (Ordinance 009, 2025).
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 $644 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 — Fort Collins, CO. Data updated September 9, 2026. https://www.olerra.com/adu-calculator/fort-collins/ <a href="https://www.olerra.com/adu-calculator/fort-collins/">Fort Collins 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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