Accessory dwelling unit permit — Longmont, CO
Last updated: September 24, 2026
What affects the price
Building an ADU is a custom project, so costs vary based on your specific choices. Site conditions are the biggest factor; if your land requires significant grading, utility extensions, or foundation work, those expenses add up quickly. Choosing high-end finishes, custom cabinetry, or complex roof lines will also push the budget higher compared to a standard design. Prefabricated units often offer predictable costs, while custom site-built structures allow for more flexibility but can be harder to estimate upfront. Exact pricing confirmed free on the call.
About this service
An accessory dwelling unit permit is the mandatory approval required by your city to ensure your project meets local zoning and safety codes. You need this whenever you plan to add a secondary living space to your property. Factors affecting the cost include municipal filing fees and the level of engineering detail required for your plans. Exact pricing confirmed free on the call.
Frequently asked in Longmont
What's included in an ADU quote for Longmont homeowners?
What are the rules for a detached accessory dwelling unit in Longmont?
Where can I find accessory dwelling unit builders near me in Longmont?
What does accessory dwelling unit mean in Longmont?
How much does accessory dwelling unit construction cost in Longmont?
What are the benefits of backyard accessory dwelling units in Longmont?
Also serving nearby: Boulder · Thornton · Westminster · Arvada · Greeley
More on this: HUD ADU resources — ADU policy and financing research.
Service area details
Serving all of Longmont — population 98,630; about 3,396 residents per square mile across 29.0 sq mi. ZIP codes covered include 80501, 80502, 80503, 80504.
Neighborhoods served in Longmont: Downtown Longmont, Mountain View, Parkside, Old Town, The Peaks — and every surrounding area.
Areas we serve
Browse by state, then city.