Building an ADU in Northern Colorado: What the Law Changed and What It Still Costs
- Aug 11
- 4 min read
The headline version of Colorado's accessory dwelling unit law is simple. You can build a backyard unit now.
The version you meet at the permit counter is more complicated, and the gap between the two is roughly twenty thousand dollars.
Who the Law Actually Binds
House Bill 24-1152 passed in 2024, and it applies to what the statute calls subject jurisdictions. Per the bill text published by the Colorado General Assembly, that means a municipality with a population of 1,000 or more sitting inside a metropolitan planning organization, plus certain unincorporated areas inside large census designated places within an MPO.
Fort Collins and Loveland both qualify. Most of unincorporated Larimer County does not, which surprises people who assume a state law lands everywhere at once.
On or after June 30, 2025, subject jurisdictions have to allow one accessory dwelling unit as an accessory use to a single-unit detached dwelling anywhere they already allow single-unit detached dwellings, and they have to approve it administratively. No public hearing. No neighborhood vote. The City of Fort Collins says the state law opened ADUs across all its zone districts starting February 2025.
The word doing the heavy lifting is "administratively." It does not mean easily, and it does not mean cheaply.
What You Can Actually Build
Fort Collins publishes hard numbers:
Detached ADU: up to 750 square feet if the main home is under 1,667 square feet. Up to 1,000 square feet or 45% of the main home, whichever is less, if it is larger.
Converting an existing accessory building: up to 800 square feet.
Attached ADU above grade: up to 750 square feet or 45% of the main home.
Basement ADU: up to 750 square feet or 100% of that floor.
Detached units sit behind the front wall of the house, at least 5 feet from other buildings, and follow the zone's setbacks.
A detached ADU cannot exceed the height of the main building.
Two rules people forget: a walkway has to connect the ADU's main door to the street, and the address has to be visible from the street. And per the city, no new units are allowed in the Poudre River 100-year floodplain at all.
Loveland went further than the statute required. The city has been certified by the state as an ADU Supportive Jurisdiction since February 2026. It waives capital expansion fees for ADUs, requires no off-street parking, allows an ADU on any property with a single-family home, and lets homeowners act as their own general contractor. Loveland has also signaled interest in extending ADUs to duplex and townhome lots.
That last provision is more generous than it sounds, and more dangerous. Acting as your own GC means you own the schedule, the subs, and every inspection failure.
The Fee Conversation Nobody Has Early Enough
Fort Collins lists a mandatory Basic Development Review flat fee of $6,925 for ADU projects. Add water, sewer and electric capacity charges, Larimer County road impact fees, city capital expansion fees, and a building permit priced off project value, and the city's own published estimate for total ADU fees lands between $20,000 and $25,000.
That is before a single stud.
Two more line items ambush budgets. ADUs need their own electric meter in Fort Collins, and depending on your street you may be paying for a transformer upgrade or trenching. Separately, if the project creates more than 1,000 square feet of new impervious surface, counting roof and pavement together, you owe stormwater quality treatment: a rain garden, permeable pavers, something. It is worth asking a fort collins concrete contractor early whether the required walkway and any driveway change push you across that line, because the answer moves your budget, not just your landscaping.
As for return, the 2025 Cost vs. Value Report from the Journal of Light Construction puts a national-average accessory dwelling unit at $166,406 in job cost against $68,656 in resale value, or about 41% recouped. An ADU is not a flip. It is a housing decision that happens to be attached to your house.
The Order Things Happen
Fort Collins offers a free Conceptual Design Review before you apply, and skipping it is a mistake. It is the cheapest hour in the project, because staff will flag utility connections and site-specific problems before you have paid anyone to draw the wrong thing.
Then:
Basic Development Review, decided by the Planning Manager or Community Development Director. No neighborhood meeting, though notice gets posted or mailed.
Building permit. This brings fire-rated separation for attached units, separate heating systems, separate exit doors, and minimum kitchen and bath standards.
Site work. Utility trenching first, then foundation and flatwork. Schedules quietly slip here, because the pad, the walkway the city requires, and any driveway change all have to be poured and cured before framing means anything. Ask any loveland colorado concrete contractor about scheduling a pour around a Front Range spring and you will get a longer answer than you wanted.
Framing, mechanicals, inspections, finish.
Utility separation rules bite in step three. Fort Collins requires 10 feet between water and sewer lines, 10 feet between storm drains and other utilities, 6 feet between trees and water or sewer lines, and 4 feet between shrubs and the same. If you have a mature tree where the sewer needs to run, you have a decision to make, and it is usually about the tree.
Before You Call an Architect
Three checks, in this order:
Confirm your zoning and your floodplain status. Fort Collins publishes both on public maps.
Confirm which desk you are actually dealing with. Fort Collins, Loveland, and unincorporated Larimer County are three separate regimes with three separate rulebooks, and a mailing address is not proof of which one you are in.
Get a real fee number before you fall in love with a floor plan.
The state opened the door. It did not pay the toll.
