Accessory Dwelling Unit (ADU) Regulations in Longmont

Max Size- 50% of primary structure

Max Height- Cannot exceed height of primary structure

ADUs are permitted in residential and mixed-use zoning districts where single-family detached homes are allowed. Before planning an ADU, homeowners should:

• Verify zoning eligibility using Longmont’s Zoning Map.
• Ensure that the lot meets minimum size and setback requirements.
• Check if the property is located in a Planned Unit Development (PUD), as some PUDs have specific ADU regulations.

Longmont has specific size limitations and design standards to ensure ADUs fit well within existing neighborhoods:

Maximum ADU Size

• ADUs must be no more than 50% of the finished floor area of the primary residence.
• The maximum size is determined by the square footage of the main home, ensuring the ADU remains subordinate in scale.

Architectural & Design Standards

• ADUs must be visually compatible with the main home, including:
  
  • Roof pitch and materials
  • Exterior siding and trim
  • Windows and doors
• Privacy considerations: If windows face neighboring properties, they must be strategically placed or screened with fencing or landscaping.

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• HB 24-1152 requires cities to allow ADUs without designated parking, except in these cases:
  ✔ If no parking is currently required for the primary home, parking cannot be required for the ADU.
  ✔ If the lot does not have an existing parking space for the primary home, no additional parking is required.

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• ADUs must connect to the primary home’s utility services; separate water and sewer taps are not permitted.
• If the ADU is detached, additional utility connection fees may apply.

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• HB 24-1152 prohibits cities from requiring owner occupancy meaning ADUs can be rented out separately from the primary home.
• ADUs cannot be sold separately from the main home—they must remain part of the same lot.

Short-term rentals (STRs) are still prohibited, except in Planned Unit Developments (PUDs) where STRs were previously allowed.

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Under HB 24-1152, all ADU approvals must be handled administratively—meaning there are:
✔ No public hearings
✔ No subjective design reviews
✔ No neighborhood approval required

Building an ADU in Longmont requires a building permit and compliance with local regulations. The approval process includes:

1. Zoning Verification – Confirm that your lot is eligible for an ADU.
2. Design Review – Ensure that the ADU meets size, design, and setback requirements.
3. Building Permit Application – Submit site plans, architectural drawings, and supporting documents.
4. Plan Review & Approvals – The city will review the application to ensure compliance with zoning laws and building codes.
5. Construction & Inspections – Once approved, construction must follow city regulations and pass inspections before occupancy is allowed.

Permit & Fee Information

• Fees vary based on the project scope and include:
  
  • Plan review and permit fees
  • City and county taxes
  • Community investment fees

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Navigating Longmont’s ADU regulations can be complex, but Kindred Tiny Homes makes the process easy by handling every step from zoning approvals to final construction.

• We specialize in Longmont’s ADU regulations ensuring compliance with all zoning and permitting requirements.
• We provide full-service ADU development from design and engineering to construction and project management.
• We maximize your investment—creating a high-quality ADU that enhances property value and meets your needs.

If you’re considering building an ADU in Longmont, contact us today for a free consultation, we’ll guide you through your options and help bring your vision to life!

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