Cost of accessory dwelling unit — 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
The total investment for an ADU depends on several moving parts, including your property’s site conditions, the complexity of your site plan, and the high-end finishes you select. Whether you are building a detached cottage or converting a garage, costs vary based on utility connections and local labor rates. Exact pricing confirmed free on the call.
Frequently asked in Longmont
What is the process for obtaining an ADU permit in Longmont?
How do I find an ADU builder in Longmont?
What makes an ADU the 'best' option for homeowners?
What is involved in accessory dwelling unit construction?
What are homes with mother-in-law suites like in Longmont?
What influences accessory dwelling unit construction cost in Longmont?
How do I find an ADU near me 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: Old Town, Mountain View, Coleraine, Dry Creek — and every surrounding area.
Areas we serve
Browse by state, then city.