ADU Regulations in Longmont, Colorado
In Boulder County, Longmont has an established ADU program under local ordinance. Colorado's lack of a statewide mandate means Longmont's municipal code sets all requirements for accessory dwelling units.
Below is a summary of the key zoning rules applicable to Accessory Dwelling Units in Longmont as of 2026. Regulations are governed by local zoning ordinances, as Colorado has no statewide ADU mandate (HB 24-1152 addresses transit density).
| Regulation | Requirement |
|---|---|
| Maximum Size | 1,000 sq ft |
| Property Setbacks | 5 ft rear, 5 ft side |
| Extra Parking Required | Required (1 space) |
| Owner Occupancy | Required |
Additional Local Requirements for Longmont
- Minimum lot size may apply
- Minimum 200 sq ft
- Owner occupancy may be required
- ⚠️ CO has NO statewide ADU mandate — verify with city
📥 Download the Complete Longmont ADU Cheat Sheet
Get the step-by-step permit checklist, official government forms, direct planning department contacts, and estimated fees — all in one printable PDF for Longmont, Colorado.
Download the Complete Longmont ADU Cheat Sheet — $12Frequently Asked Questions About ADUs in Longmont
Can I build an ADU in Longmont?
This Colorado city regulates ADUs through local ordinance. Confirm the minimum lot size and owner occupancy rules with the planning department.
How big can my ADU be in Longmont?
What is the maximum ADU size allowed in Longmont? ADUs in Longmont can be up to 1,000 square feet, subject to the property's zoning and lot coverage limits. Always confirm the exact allowed size with the Longmont planning department before designing your project.
What about setbacks and other requirements in Longmont?
What are the setback requirements for an ADU in Longmont? ADUs in Longmont generally require setbacks of 5 ft rear, 5 ft side. California state law (AB 68) limits local setback requirements to 4 feet for existing structures, but always verify with local zoning.
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