Usually, yes. Since December 16, 2024, Denver has allowed one accessory dwelling unit on residential lots citywide, so most Sunnyside homes can add a backyard ADU or convert a basement into a garden-level unit if the project meets zoning, building code and permit rules.
Sunnyside has a lot of the ingredients people look for when they think about an ADU: alleys behind many blocks, detached garages at the back of the lot, and older homes with basements that already have a separate stair. For years, though, the answer depended on the zone district printed on your lot, and many blocks needed a rezoning before an ADU could even be designed.
That changed in late 2024, when Denver allowed ADUs in all residential areas. The question in Sunnyside now is less about whether an ADU is allowed and more about which kind fits a particular house and lot, and what it takes to make a basement legal living space.
Jason Sirois is a Denver Realtor with FORM at Compass, working out of our office at 1900 W 32nd Ave in Northwest Denver. This post covers what Denver allows, how a garden-level unit differs from a backyard cottage, how Sunnyside’s zoning and conservation overlays fit in, and what an ADU means when you sell or buy.
Can I build an ADU on my Sunnyside lot?
In most cases, yes. Denver City Council passed the citywide ADU change on November 18, 2024, and it took effect December 16, 2024. According to the city’s Citywide ADUs page, it opened about 70% of Denver’s land to ADUs, up from 36%, and removed the need to rezone a lot first.
Sunnyside runs from West 38th Avenue north to I-70, and from Federal Boulevard east to the rail line. Its residential blocks are mostly in Urban single-unit districts such as U-SU-C and U-SU-B1, with some two-unit U-TU-C blocks. An ADU is a smaller, self-contained home on the same lot as the main house, with its own kitchen, bathroom and sleeping area. In Denver it can take several forms:
- A detached backyard cottage or an apartment over a garage
- An attached addition to the house
- Converted space inside the house, such as a basement or attic
An ADU is not a separate property and cannot be sold on its own. In single-unit districts, the limit is one ADU per zone lot, and it must be smaller than the zoning allowance for the main house.
Can I turn my basement into a garden-level unit?
Often, and for many Sunnyside homes it is the more practical route, because the structure already exists. A garden-level unit is an interior ADU, so it follows the same zoning rules on number and use. The harder part is usually the building code, because a basement has to meet the standards for a separate dwelling, not just a finished rec room.
The main items a designer will check are set by the International Residential Code, as adopted and amended by Denver:
- Emergency escape. Sleeping rooms need an egress window or door. The model code calls for a net clear opening of at least 5.7 square feet, at least 24 inches high and 20 inches wide, with the sill no more than 44 inches above the floor, plus a window well large enough to climb out of.
- Ceiling height. Habitable rooms generally need at least 7 feet, with limited allowances for beams and ducts.
- Fire separation. Two dwelling units in one building need a fire-rated separation between them, which affects the ceiling, stair and any shared mechanical room.
- Utilities and sewer. New living space needs a sewer use and drainage permit, and an older sewer line sometimes has to be replaced.
Low ceilings, small window openings and a furnace room in the middle of the floor plan are the usual reasons a basement conversion costs more than expected. A site visit from an architect or contractor familiar with Denver ADUs will tell you quickly which of these apply.
How big can a backyard ADU be in Sunnyside?
Size and shape come from the zone district’s building form standards. The city’s Constructing Accessory Dwelling Units guide summarizes the main limits:
| Standard | What the city’s summary says |
|---|---|
| Location on the lot | Detached ADUs go in the rear 35% of the lot |
| Floor area, zone lot 7,000 sq ft or less | Up to 864 sq ft |
| Floor area, zone lot over 7,000 sq ft | Up to 1,000 sq ft |
| Height, Urban neighborhood context | Two stories and 24 feet |
| Vehicle access | From the alley if one exists |
Source: City and County of Denver, Constructing Accessory Dwelling Units (updated June 13, 2023). The Denver Zoning Code controls; confirm your district on the city’s zoning map.
Sunnyside also has two conservation overlays that City Council adopted in February 2023, which the Denver Gazette covered at the time. They apply to new construction, cap house size on smaller lots, adjust side bulk planes and, in one overlay, call for brick. They do not change which uses are allowed, but they can affect the design of an addition or a new structure, so ask your designer to check whether your lot is in one.
Do I have to live there, and can I rent the ADU?
Under Denver’s current rules, the owner must live in the main house when applying for ADU permits, unless the house and ADU are built at the same time. After that, the ADU can stay in use even if the owner later moves. That follows Colorado’s 2024 ADU law, House Bill 24-1152, which limits owner-occupancy requirements to the permit application and short-term rental licensing.
Long-term rental of an ADU is allowed. Short-term rentals are licensed separately in Denver and are tied to the host’s primary residence, so check those rules before counting on nightly rental income. Parking is rarely the obstacle it used to be: the state law generally bars covered cities from requiring a new space for an ADU, and Denver eliminated minimum parking requirements in 2025.
On U-TU-C blocks, zoning also allows two-unit homes, which gives some owners a different path than an ADU. The rules for that route differ, so it is worth comparing both with a designer before committing.
What does an ADU mean when you buy or sell in Sunnyside?
A permitted ADU is part of the property and transfers with it. When a listing mentions a garden-level unit, carriage house or “in-law suite,” the questions that matter are about permits and the structure:
- Is there a certificate of occupancy for the unit, or was it finished as a family room or studio?
- Do the basement bedrooms have code-compliant egress windows?
- Does the unit share meters, a furnace or a water heater with the main house?
- When was the sewer line last scoped?
Our Berkeley post on building a backyard ADU under Denver’s citywide rules covers the detached-ADU permit steps in more detail, and our Sunnyside community page has neighborhood context and current listings. If you are weighing an ADU, a sale or a purchase in Sunnyside, Jason Sirois and the FORM Team at Compass Denver are glad to look at a specific address with you.
Frequently Asked Questions
Are ADUs allowed in Sunnyside, Denver?
Yes. Since December 16, 2024, Denver has allowed ADUs in all residential areas, so most Sunnyside lots no longer need a rezoning. Each project still has to meet the zone district’s form standards and pass permit review.
Is a basement apartment an ADU in Denver?
A self-contained unit inside the house, with its own kitchen, bathroom and sleeping area, is an interior ADU. It needs permits and has to meet building code for a separate dwelling, including egress and fire separation.
What does a basement need to become a legal garden-level unit?
Typically an egress window or door for sleeping rooms, adequate ceiling height, a fire-rated separation from the main house, and permitted plumbing and sewer work. An architect or contractor can confirm what your basement needs.
How big can a detached ADU be in Sunnyside?
The city’s summary allows up to 864 square feet on zone lots of 7,000 square feet or less and up to 1,000 square feet on larger lots, up to two stories and 24 feet in the Urban context, placed in the rear 35% of the lot.
Do I need to live on the property to build an ADU?
You need to live in the main house when you apply for permits, unless the house and ADU are built together. The ADU can stay in use if you later move.
Can I use an ADU as a short-term rental in Sunnyside?
Denver licenses short-term rentals separately and ties them to the host’s primary residence. Check the city’s short-term rental rules for your situation before planning on nightly rentals.
This article is general information based on City and County of Denver, State of Colorado and news materials available as of November 9, 2026. It is not legal, tax or financial advice. Zoning, building code and permit rules change and vary by lot; confirm requirements for your address with Denver Community Planning and Development and a licensed design professional.
