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Accessory Dwelling Unit (ADU) Permit in Lyons, Colorado

Required for construction of an Accessory Dwelling Unit (basement/attic apartment, addition, detached structure, or certified Tiny Home on Wheels) in the Town of Lyons. ADUs are approved through the standard building permit process (no separate use permit) in all zone districts that allow single-unit dwellings, subject to the Town's ADU Standards and Rules.

Verified 2026-07-06 · Source

When you need this permit

  • Permitted in all zone districts allowing single-unit dwellings: R-1, R-2, R-2A, E, E-C, and any other zone district permitting single-unit homes
  • Minimum size subject to applicable IRC requirements; maximum size equals the principal dwelling unit's size, or up to 800 sq ft if the principal unit is 800 sq ft or smaller (no size cap for a basement ADU)
  • Maximum height per the underlying zone district: 30 ft (R-1, R-2, R-2A, E, A-1, A-2) or 35 ft (E-C)
  • Subject to principal-building front/side setbacks and accessory-building rear setback requirements (or principal-building rear setback if the ADU is attached/internal)
  • One ADU permitted per lot; two permitted if the lot exceeds 0.5 acres (21,780 sq ft); more than two on lots over 1 acre requires Community Development Department guidance
  • No off-street parking requirement, no owner-occupancy requirement, no deed restriction required
  • Short-term rentals (under 30 days) are prohibited in an ADU
  • Detached ADUs under 800 sq ft do not require fire sprinklers; internal/attached ADUs do not require fire separation if smoke/CO alarms are interconnected with the principal dwelling
  • Mobile homes, manufactured homes, and RVs may not be used as ADUs (certified Tiny Homes on Wheels may qualify with Community Development Department guidance)
  • If the ADU does not meet these standards, a variance may be requested through the Community Development Department

Required documents

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Fee schedule

Building Permit Fee (same valuation-based schedule as new construction)
$135 minimum, scaling per the valuation tiers in the Town's fee schedule
Plan Review Fee
65% of the Building Permit Fee
Utility connection feesADUs are not required to pay water tap, sewer tap, or electric community investment fees per the Town's ADU Standards and Rules
$0

Review timeline

Plan review
Not published — contact the department

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

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

Inspection process

  1. 1

    Foundation

    Before concrete pour (new detached ADU only)

  2. 2

    Framing

    Structural framing complete before cover

  3. 3

    Rough Electrical / Plumbing / Mechanical

    Trade rough-ins before concealment

  4. 4

    Final Inspection

    All work complete per approved plans, including interconnected smoke/CO alarms for attached/internal ADUs without fire separation

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

Tips

  • Lyons explicitly waives water tap, sewer tap, and electric community investment fees for ADUs — a meaningful cost advantage compared to a standalone new dwelling unit.
  • A basement ADU has no maximum size cap under the Town's rules, unlike an addition or detached ADU, which are capped at the principal dwelling's size (or 800 sq ft if the principal unit is smaller).
  • Short-term rentals under 30 days are explicitly prohibited in a Lyons ADU — plan for long-term/workforce housing use only, though the Town notes incentives may be available for offering affordable rental rates.

Frequently asked questions

No. ADUs are approved through the standard building permit process. If a proposed ADU does not meet the Town's published standards, the property owner can pursue a variance through the Community Development Department instead of a separate use-permit track.

In Lyons, the published Building Permit Fee (same valuation-based schedule as new construction) is: $135 minimum, scaling per the valuation tiers in the Town's fee schedule. Additional published fees: Plan Review Fee — 65% of the Building Permit Fee; Utility connection fees — $0. These are the jurisdiction's own published figures — see the fee schedule table and source citations on this page.

Lyons does not publish a plan-review timeline for this permit. Contact Town of Lyons Planning and Building Department (permit processing, plan review, and inspections contracted to SAFEbuilt) at 303-823-6622 ext. 25 (Town Planning and Building Director); 970-545-3512 (SAFEbuilt Permit Technician); 970-545-3555 (SAFEbuilt Chief Building Official); 303-774-0454 (Inspection Request Line) for current turnaround.

You'll need: Building Permit Application; Submittal Requirements for New Detached Residential Structures (checklist). See the required-documents checklist on this page for details on each.

Lyons requires 4 inspection(s) for an accessory dwelling unit (adu) permit, in order: Foundation, Framing, Rough Electrical / Plumbing / Mechanical, Final Inspection. Schedule each through Town of Lyons Planning and Building Department (permit processing, plan review, and inspections contracted to SAFEbuilt) (303-823-6622 ext. 25 (Town Planning and Building Director); 970-545-3512 (SAFEbuilt Permit Technician); 970-545-3555 (SAFEbuilt Chief Building Official); 303-774-0454 (Inspection Request Line)).

Apply through Town of Lyons Planning and Building Department (permit processing, plan review, and inspections contracted to SAFEbuilt) at 432 5th Avenue, Lyons, CO 80540 (PO Box 49). Phone: 303-823-6622 ext. 25 (Town Planning and Building Director); 970-545-3512 (SAFEbuilt Permit Technician); 970-545-3555 (SAFEbuilt Chief Building Official); 303-774-0454 (Inspection Request Line), email: Lritchie@townoflyons.com (Lisa Ritchie, Planning and Building Director); dtoberman@safebuilt.com (Danielle Toberman, Permit Technician); tmoroney@safebuilt.com (Tim Moroney, Chief Building Official). Office hours: Monday-Thursday 8:00 a.m.-4:30 p.m.; Friday 8:00 a.m.-noon; closed holidays. Town of Lyons main line 303-823-6622.. Official information: https://www.lyonscolorado.com/834/Building-Department.

Lyons, Colorado has adopted: 2021 International Building Code (IBC) — currently in effect per the Town of Lyons Building Department page and the Town's published Adopted Codes flyer; 2021 International Residential Code (IRC); 2021 International Plumbing Code (IPC); 2021 International Mechanical Code (IMC); 2021 International Fuel Gas Code (IFGC); 2021 International Energy Conservation Code (IECC) — the Town's 2025 Residential Submittal Checklist explicitly requires '2021 IECC Energy Code compliance for the specific home being proposed' via REScheck or an Energy Compliance Report; 2021 International Fire Code (IFC); 2021 International Property Maintenance Code (IPMC); 2021 International Existing Building Code (IEBC); 2023 National Electrical Code (NEC); Transition note: the Town of Lyons Building Department page (fetched 2026-07-06) states the 2021 ICC series and 2023 NEC apply 'until July 1, 2026,' with a 2024 ICC series adopted to take effect July 1, 2026. As of this file's lastVerified date (2026-07-06, five days after that effective date), the Town's own Adopted Codes flyer (townoflyons.com/DocumentCenter/View/932/Lyons-Design-Criteria) and Building Department page still list the 2021 series/2023 NEC as the current codes with no updated flyer found reflecting the 2024 series live — recommend confirming directly with SAFEbuilt/the Building Department (970-545-3555) whether the 2024 ICC series has been operationally rolled out before finalizing a code analysis for any permit filed on or after 2026-07-01.; State of Colorado Wildfire Resiliency Code (Ordinance 1210) — effective July 1, 2026, adopted townwide for Class 1 and Class 2 requirements applicable to new commercial/residential construction and qualifying alterations to existing structures (roof replacement 25%+, exterior wall replacement 25%+, additions adding 500+ sq ft, and new/replacement fences or decks); per the Town of Lyons Wildfire Resiliency Code Requirements page.. Local amendments apply — see the Lyons overview page for the full list.

One ADU is permitted per lot by default. If the lot is larger than 0.5 acres (21,780 sq ft), two ADUs are permitted. Requests for more than two ADUs on lots over 1 acre require contacting the Community Development Department for guidance.

Sources & verification

Verified against official sources. Last reviewed 2026-07-06.

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 Lyons building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.

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