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Accessory Dwelling Unit (ADU) Permit in Lone Tree, Colorado

The City of Lone Tree does not publish a dedicated ADU ordinance, zoning allowance summary, or standalone ADU permit page. RE-CHASED 2026-07-23 directly against the live, current (May 22, 2026 codified version) Lone Tree Municipal Code on Municode: Chapter 16 (Zoning), Article VII (SR Suburban Residential District, which governs virtually all single-family residential zoning) lists 'Principal Uses' (Sec. 16-7-20, limited to one single-family dwelling per lot), 'Accessory Uses' (Sec. 16-7-30), and 'Accessory Buildings and Uses in SR-E, SR-L and SR-M Subzoning Districts' (Sec. 16-7-300) in full, and none of these lists include 'accessory dwelling unit,' 'ADU,' or a second dwelling unit as a permitted use — accessory uses are limited to private garages, home occupations, satellite dishes, small water/wastewater facilities, and swimming pools; accessory buildings in the SR-E/L/M subzones are limited to detached garages, home occupations, maintenance buildings, private pools/greenhouses, storm shelters, and tennis courts/BBQ pits/water features. Separately, Sec. 6-6-40(b) of the Municipal Code ('Short-term rental of non-primary residences and accessory dwelling units prohibited') confirms the City's code does recognize 'accessory dwelling unit' as a term, but only in the context of banning its short-term rental — not as an established zoned use. An ADU project (where the parcel's zone district happens to allow a second dwelling, e.g. via a Planned Development zoning overlay under Article XV, or via a variance/rezoning) would be processed as a standard Residential Addition/New Construction building permit through the Accela portal, subject to the same Design Criteria, soils-test amendment, and shared valuation-based fee table as other residential work — but the standard SR-district zoning does not permit a second dwelling unit by right.

Verified 2026-07-23 · Source

When you need this permit

  • No dedicated ADU permit type, ordinance summary, or standalone process page could be located on the City's Building, Planning, Permits-and-Applications pages, or via a site search for 'accessory dwelling unit'
  • RE-CHASED 2026-07-23: the live, current Lone Tree Zoning Code (Chapter 16, Article VII, Secs. 16-7-20/16-7-30/16-7-300) does not list an ADU or second dwelling unit as a permitted principal, accessory, or special-review use in the SR Suburban Residential District — the principal-use list caps residential lots at one single-family dwelling; an ADU is NOT a use-by-right under the standard residential zoning as currently codified
  • Zoning allowance for a second dwelling unit, if achievable at all, would require a case-specific zoning review with the Planning Division (720-509-1180) — e.g. via a Planned Development (PD) zone district (Article XV), rezoning (Article XXV), or variance (Article XXVI) — prior to any building-permit application
  • If a zoning path is secured, the construction itself would be processed as a standard building permit (new construction or addition scope) subject to the same 2021 IRC/IBC-based requirements, soils test (Section 105.3.8 amendment), and Design Criteria as other residential construction
  • Colorado Wildfire Resiliency Code mitigation may apply if the ADU adds 500+ sq ft or the parcel is in a mapped fire-intensity zone

Required documents

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Fee schedule

Permit Fee (same valuation-based schedule as new construction/additions)No ADU-specific fee line exists in the published fee schedule; billed under the general Building Permit Fee table
$23.50 minimum, scaling per the valuation tiers in the 2026 Building Fees schedule
Plan Review Fee
65% of Permit Fee, minimum $100.00

Review timeline

Plan review
Not published — contact the department

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

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, if new footings are required

  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

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

Tips

  • Confirm ADU zoning eligibility with the Planning Division (720-509-1180) BEFORE assuming a building permit can be filed — the City's zoning code (Chapter 16) and specific zone district (not the Building Division) govern whether an ADU is allowed on a given parcel at all.
  • This permit type is modeled from the standard residential building-permit process since Lone Tree publishes no dedicated ADU program; treat it as a starting-point estimate, not a confirmed ADU-specific fee or process.
  • Confirmed 2026-07-23 against the live Zoning Code: an ADU is NOT a listed permitted use (principal, accessory, or special-review) in the standard SR Suburban Residential District — do not assume a second dwelling unit is achievable by right on a typical single-family lot; it would require a Planned Development, rezoning, or variance route reviewed case-by-case by Planning.

Frequently asked questions

Lone Tree requires an accessory dwelling unit (adu) permit for: No dedicated ADU permit type, ordinance summary, or standalone process page could be located on the City's Building, Planning, Permits-and-Applications pages, or via a site search for 'accessory dwelling unit'; RE-CHASED 2026-07-23: the live, current Lone Tree Zoning Code (Chapter 16, Article VII, Secs. 16-7-20/16-7-30/16-7-300) does not list an ADU or second dwelling unit as a permitted principal, accessory, or special-review use in the SR Suburban Residential District — the principal-use list caps residential lots at one single-family dwelling; an ADU is NOT a use-by-right under the standard residential zoning as currently codified; Zoning allowance for a second dwelling unit, if achievable at all, would require a case-specific zoning review with the Planning Division (720-509-1180) — e.g. via a Planned Development (PD) zone district (Article XV), rezoning (Article XXV), or variance (Article XXVI) — prior to any building-permit application; If a zoning path is secured, the construction itself would be processed as a standard building permit (new construction or addition scope) subject to the same 2021 IRC/IBC-based requirements, soils test (Section 105.3.8 amendment), and Design Criteria as other residential construction; Colorado Wildfire Resiliency Code mitigation may apply if the ADU adds 500+ sq ft or the parcel is in a mapped fire-intensity zone. If your project isn't listed, confirm with City of Lone Tree Community Development Department, Building Division at 720-390-5211 before starting work.

In Lone Tree, the published Permit Fee (same valuation-based schedule as new construction/additions) is: $23.50 minimum, scaling per the valuation tiers in the 2026 Building Fees schedule. Additional published fees: Plan Review Fee — 65% of Permit Fee, minimum $100.00. These are the jurisdiction's own published figures — see the fee schedule table and source citations on this page.

Lone Tree does not publish a plan-review timeline for this permit. Contact City of Lone Tree Community Development Department, Building Division at 720-390-5211 for current turnaround.

You'll need: Building Permit Application. See the required-documents checklist on this page for details on each.

Lone Tree requires 4 inspection(s) for an accessory dwelling unit (adu) permit, in order: Foundation, Framing, Rough Electrical / Plumbing / Mechanical, Final Inspection. Schedule each through City of Lone Tree Community Development Department, Building Division (720-390-5211).

Apply through City of Lone Tree Community Development Department, Building Division at 9220 Kimmer Dr., Suite 100, Lone Tree, CO 80124. Phone: 720-390-5211, email: building@cityoflonetree.com. Office hours: 7:00 AM - 4:00 PM, Monday-Friday, excluding holidays/weekends. Chief Building Official: Matt Archer. Community Development Director: Kelly First (kelly.first@cityoflonetree.com, 720-509-1274). General city line: 303-708-1818.. Official information: https://cityoflonetree.com/community-development/building/.

Lone Tree, Colorado has adopted: 2021 International Building Code (IBC), as amended — City of Lone Tree Design Criteria & Codes page; 2021 International Residential Code (IRC), as amended; 2021 International Fire Code (IFC); 2021 International Plumbing Code (IPC); 2021 International Mechanical Code (IMC); 2021 International Fuel Gas Code (IFGC); 2021 International Energy Conservation Code (IECC); 2023 National Electrical Code (NEC); 2017 ICC A117.1 Accessibility Code; Note on Chapter 18 (Building Regulations), Lone Tree Municipal Code: search-indexed content confirms the City has adopted the International Building Code, 2021 Edition, as amended, with a certified copy on file with the City Clerk; a local amendment adds Section 105.3.8 'Soils Test,' requiring a soils test prepared by a Colorado-registered professional engineer at building permit application, with an engineering geologist additionally required for hillside/geological-hazard/steep-slope sites at the Building Official's discretion. Full text of Chapter 18 could not be independently re-verified beyond this indexed excerpt because library.municode.com/co/lone_tree serves an Angular single-page app shell (empty of code text without JS rendering) and returned HTTP 403 to both a standard fetch and a full-browser-header curl retry — this is a partial-confidence caveat on the amendment-detail level only, not on the base code-edition list, which is independently confirmed on the City's own actively-maintained Design Criteria & Codes page.; HB22-1362 statewide energy floor (Colorado): as of 2026-07-06 (this review date), HB22-1362 requires that municipalities/counties updating their building code adopt an energy code achieving equivalent-or-better performance than the 2021 IECC + Model Electric and Solar Ready Code (effective window 7/1/2023-6/30/2026), stepping up to the Colorado Energy Code Board's Model Low Energy and Carbon Code (published 9/2/2025) as the new statewide minimum for any code update on or after 7/1/2026. Lone Tree's currently-published adopted energy code is the 2021 IECC (per its own Design Criteria & Codes page, most recent update not dated on-page) — this predates the 7/1/2026 Model Low Energy and Carbon Code trigger point and does not itself violate HB22-1362, since that stricter floor applies only when a jurisdiction next updates its code. Flagged honestly rather than assumed; confirm current status with the Building Division (720-390-5211) before relying on this for a 2026-cycle project, since Lone Tree could adopt updated codes at any time.. Local amendments apply — see the Lone Tree overview page for the full list.

No. The City does not publish a standalone ADU ordinance summary or permit page, and — confirmed directly against the live, current Zoning Code (Chapter 16, Article VII, Secs. 16-7-20/16-7-30/16-7-300) on 2026-07-23 — an ADU is not listed as a permitted use of any kind in the standard SR Suburban Residential District, which caps residential lots at one single-family dwelling. A second dwelling unit would require a case-specific zoning path (Planned Development, rezoning, or variance) reviewed by the Planning Division, and if approved, construction would be processed as a standard building permit through the Building Division.

Sources & verification

Verified against official sources. Last reviewed 2026-07-23.

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

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