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Accessory Dwelling Unit (ADU) Permit in Windsor, Colorado

Required for construction of an ADU in Windsor, a two-step process: first a Planning Department land-use application/approval (Municipal Code Sec. 14-2-100 zoning eligibility, Sec. 16-3-40 ADU regulations), then a standard building permit once the ADU land-use application is approved and recorded.

Verified 2026-07-06 · Source

When you need this permit

  • ADUs are permitted as an accessory use in conjunction with all single-family detached dwellings in all zoning districts that permit single-family dwelling units
  • ADU living space must be between 500 and 950 square feet, and the ADU's living space may not be larger than the living space of the principal dwelling
  • A single-family dwelling must already exist as the principal dwelling on the lot, or be constructed in conjunction with the ADU; a Certificate of Occupancy will only be granted to the ADU after it has been granted to the principal dwelling
  • An existing off-street parking space (driveway, garage, tandem parking, other off-street space, or on-street parking) must be available for designation to the ADU
  • ADU must be compatible in design with the principal dwelling; photos of the principal home plus proposed ADU elevations (front and side) are required
  • Type I (detached), Type II (attached/internal, locked off from the principal dwelling, considered a separate dwelling unit under the building code), and Type III (attached/internal, NOT locked off, considered part of one dwelling unit under the building code) are the three defined ADU types
  • A Declaration of Restrictive Covenants must be recorded: the property owner (Declarant) must reside on the property as their primary residence (with a short-term-rental exception allowing residence in either the principal dwelling or the ADU while an STR permit is active); ADU ownership cannot be transferred separately from the principal dwelling, nor may the property be subdivided; the ADU is restricted to its approved size
  • Two (2) sets of architectural/floor plans, engineered foundation plans (wet-stamped by a Colorado-licensed engineer for new detached structures), electrical plans, mechanical plans, fire separation assemblies (a listed 2-hour fire-rated horizontal/vertical assembly separating units per the IRC), and (if applicable) stamped fire protection plans are required
  • Two (2) copies of Manual J and Manual D compliance calculations, plus IECC energy code compliance documentation (ResCheck or an energy rating company report), are required
  • A soils report and Site Grading Certificate must be approved by the Town before a Certificate of Occupancy is issued
  • Once the ADU land-use application is approved and recorded with the county, the applicant may then submit for the actual building permit
  • Type I ADU site plans must be prepared and signed by a Colorado Licensed Surveyor or Engineer

Required documents

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Fee schedule

ADU Application FeeFee amount not legible in the Town's own Fee Schedule PDF extraction for this specific line item (Planning Fees section, '14-2-100 Accessory Dwelling Unit'); contact the Planning Department directly for the current dollar figure. Genuinely could not extract a clean number despite direct PDF review — flagged rather than guessed.
Per the Town of Windsor Fee Schedule (Code Section 14-2-100)
Building Permit Fee (for the subsequent building permit stage)Standard Building Permit Fee + 25% Windsor Administration Fee + 3.65%-of-half-valuation Use Tax apply once the ADU proceeds to the building permit stage
Equal to SAFEbuilt's own valuation-based fee

Review timeline

Plan reviewWindsor’s published plan-review target
30–90 business days

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

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

Inspection process

  1. 1

    Foundation

    Wet-stamped engineered foundation plan verified before concrete pour (new detached structures)

  2. 2

    Framing / Fire Separation

    Framing complete; 2-hour fire-rated horizontal/vertical assembly separation verified for Type I/II ADUs

  3. 3

    Rough Electrical/Mechanical

    Panel locations, receptacles, 50% efficiency lighting plan, mechanical equipment/ductwork verified before concealment

  4. 4

    Final Inspection

    All work complete; Certificate of Occupancy withheld until the principal dwelling itself already holds a Certificate of Occupancy

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

Tips

  • Windsor's ADU process is two distinct stages: a Planning Department land-use application/zoning approval FIRST (1-3 months per the Town's own page), THEN a standard building permit through SAFEbuilt — budget for both stages sequentially, not concurrently.
  • The ADU size window (500-950 SF, and never larger than the principal dwelling's own living space) is a two-sided cap unlike some jurisdictions that only cap the maximum — check both bounds.
  • A Certificate of Occupancy for the ADU will not be granted until the principal dwelling itself already holds one — relevant if you're building both simultaneously as new construction.
  • The Declaration of Restrictive Covenants is a real recorded legal instrument, not just a checklist item — it binds successors in ownership and restricts the ADU from ever being sold/subdivided separately from the principal home.
  • An optional no-fee concept-plan review is available before the formal application — worth using given the two-stage process and the value of catching zoning issues early.

Frequently asked questions

Windsor requires an accessory dwelling unit (adu) permit for: ADUs are permitted as an accessory use in conjunction with all single-family detached dwellings in all zoning districts that permit single-family dwelling units; ADU living space must be between 500 and 950 square feet, and the ADU's living space may not be larger than the living space of the principal dwelling; A single-family dwelling must already exist as the principal dwelling on the lot, or be constructed in conjunction with the ADU; a Certificate of Occupancy will only be granted to the ADU after it has been granted to the principal dwelling; An existing off-street parking space (driveway, garage, tandem parking, other off-street space, or on-street parking) must be available for designation to the ADU; ADU must be compatible in design with the principal dwelling; photos of the principal home plus proposed ADU elevations (front and side) are required; Type I (detached), Type II (attached/internal, locked off from the principal dwelling, considered a separate dwelling unit under the building code), and Type III (attached/internal, NOT locked off, considered part of one dwelling unit under the building code) are the three defined ADU types; A Declaration of Restrictive Covenants must be recorded: the property owner (Declarant) must reside on the property as their primary residence (with a short-term-rental exception allowing residence in either the principal dwelling or the ADU while an STR permit is active); ADU ownership cannot be transferred separately from the principal dwelling, nor may the property be subdivided; the ADU is restricted to its approved size; Two (2) sets of architectural/floor plans, engineered foundation plans (wet-stamped by a Colorado-licensed engineer for new detached structures), electrical plans, mechanical plans, fire separation assemblies (a listed 2-hour fire-rated horizontal/vertical assembly separating units per the IRC), and (if applicable) stamped fire protection plans are required; Two (2) copies of Manual J and Manual D compliance calculations, plus IECC energy code compliance documentation (ResCheck or an energy rating company report), are required; A soils report and Site Grading Certificate must be approved by the Town before a Certificate of Occupancy is issued; Once the ADU land-use application is approved and recorded with the county, the applicant may then submit for the actual building permit; Type I ADU site plans must be prepared and signed by a Colorado Licensed Surveyor or Engineer. If your project isn't listed, confirm with Town of Windsor Community Development / Building Permits (Building Division contracted to SAFEbuilt) at 970-674-2436 (Permit Technician); 970-674-2400 (Town main line, option 4 for Building Permits/Community Development); SAFEbuilt Inspections 970-674-1036 or 1-866-671-1036 before starting work.

In Windsor, the published ADU Application Fee is: Per the Town of Windsor Fee Schedule (Code Section 14-2-100). Additional published fees: Building Permit Fee (for the subsequent building permit stage) — Equal to SAFEbuilt's own valuation-based fee. These are the jurisdiction's own published figures — see the fee schedule table and source citations on this page.

The Town's own ADU page states the review period is one to three months, depending on review comments and how quickly the applicant responds; this covers the Planning Department land-use approval stage prior to the separate building permit.

You'll need: Accessory Dwelling Unit Application Packet; Site Plan Submittal Documents; SAFEbuilt Accessory Dwelling Unit Submittal Checklist; Recorded Deed. See the required-documents checklist on this page for details on each.

Windsor requires 4 inspection(s) for an accessory dwelling unit (adu) permit, in order: Foundation, Framing / Fire Separation, Rough Electrical/Mechanical, Final Inspection. Schedule each through Town of Windsor Community Development / Building Permits (Building Division contracted to SAFEbuilt) (970-674-2436 (Permit Technician); 970-674-2400 (Town main line, option 4 for Building Permits/Community Development); SAFEbuilt Inspections 970-674-1036 or 1-866-671-1036).

Apply through Town of Windsor Community Development / Building Permits (Building Division contracted to SAFEbuilt) at 200 N. 11th Street, Windsor, CO 80550 (Permit Technician); Planning Department at 301 Walnut Street, Windsor, CO 80550. Phone: 970-674-2436 (Permit Technician); 970-674-2400 (Town main line, option 4 for Building Permits/Community Development); SAFEbuilt Inspections 970-674-1036 or 1-866-671-1036, email: SAFEbuilt inspection requests: inspect@safebuilt.com. Town Permit Technician (Robin Volner, per the Multi-Family Building Permit Fee Estimate form): rvolner@windsorgov.com. Office hours: Monday-Thursday, 8 a.m. to 5 p.m.; online services available Fridays (Town offices are closed to walk-in service on Fridays per the Building Permits page). Official information: https://www.windsorco.gov/137/Building-Permits.

Windsor, Colorado has adopted: 2024 International Codes (I-Codes), adopted with an effective date of January 1, 2026 — Town of Windsor Building Permits page (verbatim: 'The 2024 I-Codes have been adopted with the effective date of January 1, 2026') states all new building plans, including master plans and energy code submissions, are reviewed under the 2024 I-Codes as of that date. Source: https://www.windsorco.gov/137/Building-Permits; 2023 National Electrical Code (NEC), effective for permit applications submitted on or after January 1, 2024 — per the Town's own '2023 NEC Adoption Letter — Windsor' PDF referenced from the Building Permits page; 2025 Colorado Wildfire Resiliency Code (CWRC), adopted by the Colorado Wildfire Resiliency Code Board (WRCB) effective July 1, 2025 (8 CCR 1507-39); the Town of Windsor's own Building Permits page states the CWRC 'will take effect in Windsor on July 1, 2026'; DATA-CURRENCY CONFLICT DISCLOSED: the Town's separately-hosted 'Design Criteria and Adopted Codes' PDF (last modified 2024-07-23, prior to the 2024 I-Codes' Jan 1, 2026 effective date) still lists a superseded code suite — 2018 IRC/IBC, 2018 IECC, 2018 IFC, 2020 NEC, 2018 IPC, 2018 IMC, 2018 IFGC, 2018 IEBC, 2018 ISPSC, all 'with Amendments' — and has evidently not been refreshed to reflect the 2024 I-Codes/2023 NEC transition confirmed directly and verbatim on the live Building Permits page. This file treats the live Building Permits page (2024 I-Codes eff. 1/1/2026, 2023 NEC eff. 1/1/2024) as the current governing code list, per the more-recent, directly-dated source. Source: https://www.windsorco.gov/DocumentCenter/View/16086/Adopted-Codes-and-Design-Criteria (PDF metadata ModDate 2024-07-23) vs. https://www.windsorco.gov/137/Building-Permits (live page, fetched 2026-07-06). Local amendments apply — see the Windsor overview page for the full list.

Between 500 and 950 square feet of living space, and never larger than the living space of the principal dwelling on the same lot.

Other permits in Windsor

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Accessory Dwelling Unit (ADU) Permit in other cities

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