Usually, yes. Applewood Knolls sits in unincorporated Jefferson County, where a detached ADU needs a lot of at least 7,500 square feet. A quarter-acre lot (about 10,890 square feet) qualifies for a detached ADU of up to 600 square feet or 40% of the home, whichever is less, with a 500-square-foot floor.
Applewood Knolls is the 1960s neighborhood around West Applewood Knolls Drive, West 27th Drive and West 26th Avenue. The homes carry Lakewood 80215 mailing addresses, but the neighborhood sits in unincorporated Jefferson County, so the county, not the City of Lakewood, sets the zoning rules that decide whether a backyard cottage can go in.
That distinction matters for accessory dwelling units, or ADUs. Colorado’s 2024 ADU law changed the rules in Lakewood, Wheat Ridge, Golden and Denver, but not in unincorporated Applewood, where Jefferson County’s own standards tie the size of a detached unit to the size of the lot.
Jason Sirois, a Realtor with FORM at Compass Denver and an Applewood resident, walks through what the county’s current rules allow on a quarter-acre lot, where Applewood Knolls lots tend to land against the county’s size thresholds, and what else has to line up before a permit is issued.
What Jefferson County allows on a quarter-acre lot
Jefferson County’s Accessory Dwelling Unit guide (revised February 4, 2025) sets three detached size tiers by lot size. A quarter acre is 10,890 square feet. That is above the 7,500-square-foot minimum for a detached unit, but below the 12,500-square-foot step that unlocks a larger one.
| Lot size | Roughly in acres | Detached ADU allowed? | Maximum detached ADU size |
|---|---|---|---|
| Under 7,500 sq ft | Under 0.17 acre | No | Attached or basement ADU only |
| 7,500 to 12,499 sq ft | About 0.17 to 0.29 acre | Yes | 600 sq ft or 40% of the home, whichever is less |
| 12,500 sq ft to under 1 acre | About 0.29 acre to under 1 acre | Yes | 800 sq ft or 40% of the home, whichever is less |
| 1 acre or more | 1 acre or more | Yes | 1,200 sq ft or 40% of the home, whichever is less |
Two footnotes in the guide change the math. First, any ADU may be at least 500 square feet regardless of the percentage cap. Second, a basement converted to an ADU is exempt from the size and percentage limits entirely. Attached ADUs follow a separate cap of 1,200 square feet or 40% of the home, whichever is less, on any lot that meets the zone district’s minimum.
How the 40% rule plays out on a real house
The percentage cap is measured against the primary home’s living space, so the same quarter-acre lot can support different ADU sizes depending on the house already on it. Here is the guide’s formula applied to three home sizes on a 10,890-square-foot lot:
| Primary home living space | 40% of the home | Tier cap | Largest detached ADU |
|---|---|---|---|
| 1,100 sq ft | 440 sq ft | 600 sq ft | 500 sq ft (the guide’s floor) |
| 1,400 sq ft | 560 sq ft | 600 sq ft | 560 sq ft |
| 1,800 sq ft | 720 sq ft | 600 sq ft | 600 sq ft |
Two more limits apply. All accessory square footage, including the ADU, garages and sheds, cannot exceed the home’s square footage, and no accessory structure’s footprint may exceed 75% of the home’s footprint. With a large detached garage already on the lot, those totals can bind before the ADU tier does.
Where Applewood Knolls lots fall against the 12,500-square-foot line
Applewood Knolls lots are not uniform, and the 12,500-square-foot threshold sits at about 0.29 acre. That means two neighboring homes can face different detached caps. A lot listed at 0.28 acre is roughly 12,200 square feet and stays in the 600-square-foot tier; a lot at 0.30 acre is roughly 13,070 square feet and moves into the 800-square-foot tier.
Listing sheets round acreage, so check the recorded lot area in Jefferson County’s property records, or a survey, before paying for design work on a lot close to 12,500 square feet.
Also confirm the jurisdiction: nearby blocks inside Lakewood or Wheat Ridge city limits follow those cities’ ADU codes instead, and the county’s property record shows which applies. For how Applewood addresses, cities and ZIP codes relate, see our post on whether Applewood is a city.
Height, setbacks, parking and utilities
Jefferson County’s ADU questions page and the guide add more requirements:
- Height: an ADU may be no taller than the primary home or 25 feet, whichever is less. Behind a single-story ranch, that generally rules out a second-story unit over a garage.
- Setbacks: a detached ADU must meet the accessory structure setbacks of the lot’s zone district.
- Driveway and parking: the ADU must share the home’s driveway, and one additional off-street parking space is required for each ADU bedroom.
- Bedrooms and occupancy: an ADU is limited to two bedrooms and no more than three occupants.
- Water and sewer: the water district and sanitation district must each provide a letter approving two dwelling units on the property.
- Design: the ADU’s architectural style must be compatible with the main house.
Zone districts and subdivision plats can add restrictions beyond the guide, and older plats sometimes carry recorded covenants. A title commitment or a call to Jefferson County Planning and Zoning at 303-271-8700 will show whether anything recorded against a specific lot limits a second unit.
Owner occupancy, renting and the permit
Jefferson County requires the owner to live in either the main house or the ADU as a primary residence. Under the county’s FAQ, the ADU can be rented, and an owner can live in the ADU and rent the main house for terms of 30 consecutive days or more, but both units cannot be rented at once. Short-term rentals fall under a separate section of the zoning resolution.
The ADU cannot be sold separately from the house without going through the county’s subdivision process. When the permit is approved, the county records a document in the property records noting that the second dwelling was permitted under its ADU rules, which is something a future buyer’s title work will show.
If a project meets the criteria, the county says only a building permit application is needed, with no public hearing.
Why the state ADU law does not apply here, and what could change
Colorado’s HB24-1152 bars many cities from requiring owner occupancy or new parking for ADUs. It covers cities within a metropolitan planning organization and, for counties, only unincorporated areas within a census-designated place of 40,000 or more. The Colorado Division of Local Government’s subject list includes Lakewood, Wheat Ridge and Golden but not unincorporated Jefferson County, and the Applewood census-designated place counted 7,833 people in 2020.
The county’s own rules are in motion, though. Jefferson County is folding its zoning resolution and land development rules into a single Unified Land Use Code, and the county has said the new code will set out specific ADU requirements, with a goal of finishing by the end of 2026. We covered the draft in what the Unified Land Use Code means for Applewood properties. Until the new code is adopted, the February 2025 guide is the standard that applies.
If you are weighing an ADU against selling, or checking whether a listing’s lot supports one, the Applewood community page is a good starting point, and Jason Sirois and the FORM Team at Compass Denver are happy to help you read the numbers.
Frequently Asked Questions
How big can a detached ADU be on a quarter-acre lot in Applewood Knolls?
Under Jefferson County’s guide, up to 600 square feet or 40% of the main home’s living space, whichever is less. If 40% works out to less than 500 square feet, the county still allows 500 square feet.
What lot size do I need for an 800-square-foot ADU in Applewood?
At least 12,500 square feet, or about 0.29 acre, and the main home has to be at least 2,000 square feet for 40% of it to reach 800. On lots of an acre or more, the cap rises to 1,200 square feet or 40%.
Do I have to live on the property if I build an ADU in unincorporated Jefferson County?
Yes. The owner must live in either the main house or the ADU as a primary residence. Colorado’s state ban on owner-occupancy rules does not apply to unincorporated Applewood.
Can I convert my basement into an ADU instead?
Yes. Jefferson County exempts basement conversions from the ADU size and percentage limits. The unit still needs utility approval letters, the parking space per bedroom and a building permit.
Can I build a two-story garage ADU behind a ranch house?
Often not. The ADU cannot be taller than the primary home or 25 feet, whichever is less, so a single-story ranch generally limits the ADU to about the same height.
This article is for general information only and reflects Jefferson County’s published ADU guide (revised February 4, 2025) as of October 2026. It is not legal, tax or construction advice. Zoning rules, plat restrictions and the county’s pending Unified Land Use Code can change what applies to a specific lot; confirm with Jefferson County Planning and Zoning before you design or build.
