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Accessory Dwelling Unit (ADU) Permit in Fort Collins, Colorado

Required for construction of a new attached or detached ADU in Fort Collins. Since February 2025, Colorado state law HB 24-1152 allows ADUs in all Fort Collins zone districts (previously limited to Old Town and select neighborhoods), and prohibits owner-occupancy requirements — ADUs may be rented out separately from the primary home. Fort Collins is home to Colorado State University, making ADUs relevant for rental/student housing demand. All ADUs require a mandatory Basic Development Review before a building permit.

Verified 2026-06-30 · Source

When you need this permit

  • No new units allowed in the Poudre River 100-year floodplain
  • Property must have (or be allowed to build) a house, duplex, or triplex on the lot
  • Most properties may add one ADU only; some zones (RUL, RF, CC, CCN, CCR, CG, CS, CL, LMN, MMN, HMN, NC, D, HC, E, I, RC) may allow a second detached house
  • Detached ADU size: up to 750 sq ft if main home is under 1,667 sq ft; up to 1,000 sq ft or 45% of main home (whichever is less) if larger; existing accessory buildings may convert up to 800 sq ft
  • Attached ADU size: above-grade up to 750 sq ft or 45% of main home; basement ADU up to 750 sq ft or 100% of that floor
  • Detached ADU height may not exceed the main building or the zone's max height; must sit behind the front wall of the home, at least 5 ft from other buildings, and follow zone setbacks
  • A walkway must connect the ADU's main door to the street, and the ADU's address must be visible from the street
  • ADU needs its own electric meter (Fort Collins Utilities); may require nearby transformer upgrade or trenching payment
  • Utility separations: 10 ft between water/sewer lines, 10 ft between storm drains and other utilities, 6 ft trees to water/sewer, 4 ft shrubs to water/sewer
  • Stormwater quality treatment (rain gardens, permeable pavers) required if the project creates more than 1,000 sq ft of new impervious surface
  • Mandatory Basic Development Review (flat $6,925 fee) precedes the building permit — decision made administratively by Planning Manager or Community Development Director per HB 24-1152 (no public hearing/subjective design review)
  • Building Code requirements: fire-rated separation between units (attached ADUs), separate heating systems (attached ADUs), minimum kitchen/bathroom standards, separate exit doors
  • Short-term rental of ADUs is prohibited, except in Planned Unit Developments (PUDs) where STRs were previously allowed

Required documents

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Fee schedule

Basic Development Review (BDR)City of Fort Collins ADU page — Step 4: Budget for Fees; also listed on Fee Schedules — Development Review Fees, Planning Services table
$6,925 (flat fee, mandatory for ADU projects)
Building Permit FeeCity of Fort Collins ADU page and Fee Schedules page
Based on project value/occupancy — see Residential Building Permit fee entry (R-3 occupancy-based rate)
Utility fees (water, sewer, electric capacity charges)City of Fort Collins ADU page — Step 4: Budget for Fees
Varies by project — not itemized as a single figure on the ADU page
Transportation fees (Larimer County road impact + City capital expansion)City of Fort Collins ADU page — Step 4: Budget for Fees
Varies by project
Total estimated ADU development fees (all-in)City of Fort Collins ADU page — Step 4: Budget for Fees; city's own stated estimate range combining BDR, utility, transportation, and building permit fees
Approximately $20,000–$25,000

Review timeline

Plan reviewTypical estimate — confirm current times with the Fort Collins building department
~0–0 business days

How long did your Accessory Dwelling Unit (ADU) Permit permit actually take in Fort Collins?

Anonymous — one question, no email. Answers are combined and only shown once at least 5 people have reported.

Inspection process

  1. 1

    Setback and Footing / Foundation

    Before concrete pour, per structural plans

  2. 2

    Rough Frame / Rough Plumbing / Rough Electric / Rough Mechanical

    Structural framing, egress windows, fire separation (attached ADUs), and trade rough-ins

  3. 3

    Insulation

    Air sealing and R-value verification before drywall

  4. 4

    Final Building

    All work complete; Certificate of Occupancy or Letter of Completion required before occupancy

See the full Fort Collins inspection guide — scheduling & re-inspection fees →

Tips

  • Since Feb. 2025 (Colorado HB 24-1152), ADUs are allowed in ALL Fort Collins zone districts, not just Old Town and select neighborhoods as before — a major recent expansion.
  • Budget for the mandatory $6,925 Basic Development Review fee BEFORE the building permit — this is required for every ADU project, with no public hearing under the state-mandated administrative review process.
  • Total all-in ADU costs (BDR + utility + transportation + building permit fees) run an estimated $20,000–$25,000 per the city's own published range — budget accordingly.
  • As a CSU (Colorado State University) college town, Fort Collins ADUs are commonly used for off-campus rental housing; HB 24-1152 prohibits the city from requiring owner-occupancy, but short-term rental of ADUs remains prohibited outside PUDs.
  • A free optional Conceptual Design Review with City staff is available before formal application — useful for CSU-adjacent rental-oriented ADU projects to flag utility/site issues early.

Frequently asked questions

Fort Collins requires an accessory dwelling unit (adu) permit for: No new units allowed in the Poudre River 100-year floodplain; Property must have (or be allowed to build) a house, duplex, or triplex on the lot; Most properties may add one ADU only; some zones (RUL, RF, CC, CCN, CCR, CG, CS, CL, LMN, MMN, HMN, NC, D, HC, E, I, RC) may allow a second detached house; Detached ADU size: up to 750 sq ft if main home is under 1,667 sq ft; up to 1,000 sq ft or 45% of main home (whichever is less) if larger; existing accessory buildings may convert up to 800 sq ft; Attached ADU size: above-grade up to 750 sq ft or 45% of main home; basement ADU up to 750 sq ft or 100% of that floor; Detached ADU height may not exceed the main building or the zone's max height; must sit behind the front wall of the home, at least 5 ft from other buildings, and follow zone setbacks; A walkway must connect the ADU's main door to the street, and the ADU's address must be visible from the street; ADU needs its own electric meter (Fort Collins Utilities); may require nearby transformer upgrade or trenching payment; Utility separations: 10 ft between water/sewer lines, 10 ft between storm drains and other utilities, 6 ft trees to water/sewer, 4 ft shrubs to water/sewer; Stormwater quality treatment (rain gardens, permeable pavers) required if the project creates more than 1,000 sq ft of new impervious surface; Mandatory Basic Development Review (flat $6,925 fee) precedes the building permit — decision made administratively by Planning Manager or Community Development Director per HB 24-1152 (no public hearing/subjective design review); Building Code requirements: fire-rated separation between units (attached ADUs), separate heating systems (attached ADUs), minimum kitchen/bathroom standards, separate exit doors; Short-term rental of ADUs is prohibited, except in Planned Unit Developments (PUDs) where STRs were previously allowed. If your project isn't listed, confirm with City of Fort Collins — Building Services at 970-416-2740 before starting work.

The City of Fort Collins estimates total ADU development fees (Basic Development Review, utility capacity charges, transportation fees, and building permit fees) in the range of $20,000–$25,000, with the mandatory Basic Development Review alone costing a flat $6,925.

Plan review for an accessory dwelling unit (adu) permit in Fort Collins typically runs 0–0 business days. This is an estimate, not a published figure — confirm current review times with City of Fort Collins — Building Services at 970-416-2740.

You'll need: Basic Development Review Application; Residential Building Permit Application (PDF, 558KB); Residential Mechanical Systems Design Submittal; Residential Energy Code Compliance Form. Depending on your project, Fort Collins may also ask for: Residential Demolition Permit (PDF, 441KB). See the required-documents checklist on this page for details on each.

Fort Collins requires 4 inspection(s) for an accessory dwelling unit (adu) permit, in order: Setback and Footing / Foundation, Rough Frame / Rough Plumbing / Rough Electric / Rough Mechanical, Insulation, Final Building. Schedule each through City of Fort Collins — Building Services (970-416-2740).

Apply through City of Fort Collins — Building Services at 281 N. College Ave., Fort Collins, CO 80524. Phone: 970-416-2740, email: BuildingServices@fortcollins.gov. Office hours: Monday–Friday, 8 a.m. to 5 p.m.. Official information: https://www.fortcollins.gov/Business/Building-and-Development/Building-Services.

Yes, long-term. Colorado HB 24-1152 (effective Feb. 2025) prohibits Fort Collins from requiring owner-occupancy, so ADUs can be rented separately from the primary home. However, short-term rental (STR) of an ADU is prohibited except within Planned Unit Developments (PUDs) that previously allowed STRs.

As of February 2025, ADUs are allowed on any lot zoned for a single-family dwelling, duplex, or triplex citywide, per Colorado HB 24-1152 — a significant expansion from Fort Collins' prior Old Town-focused ADU zoning.

Sources & verification

Verified against official sources. Last reviewed 2026-06-30.

Fees, timelines, and adopted codes are researched from each jurisdiction's published records — see how we verify. Requirements change and vary by project, so always confirm the current details with the Fort Collins building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.

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Accessory Dwelling Unit (ADU) Permit in other cities

Arvada, ColoradoAurora, ColoradoBoulder, ColoradoColorado Springs, ColoradoCommerce City, ColoradoCortez, ColoradoDenver, ColoradoFruita, Colorado

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