So you think you want to build an ADU in Denver?

First look at the Denver Zoning Standards & Requirements

Often referred to as a Carriage House, the acronym “ADU” is becoming part of the Denver residential vernacular. The abbreviation stands for “Accessory Dwelling Unit” for those who are not familiar with the term. It simply means a secondary living space or apartment that occupies a portion of the primary zone lot in addition to the primary house.

What do the composite of the words intend to mean: A residential structure that is subordinate to the primary home – Definitions from Denver Zoning Code (Chapter 13):

Structure, Accessory: A subordinate structure located on the same zone lot with the primary building, structure, or use, and which is incidental and customary to the primary building, structure, or use.

Dwelling: Any building or portion of building that is used as the residence of one or more households

In the Denver area, and Denver city proper in particular, the desire for property owners to build an ADU (secondary living space) has increased significantly. A couple scenarios in which this smaller additional dwelling makes sense:

It can be purposed as a long term or short term rental, in the sense that you have a full time tenant, or offer the space to visitors on one of the popular vacation rental websites like VRBO or Airbnb.
The classic use is to set the living space up as an independent, ancillary “apartment for members of the family, aging parents, or young “fresh on their feet” adults.
Other approaches we’ve heard of are where the primary home owners travel frequently, or want to simplify so they occupy the ADU as their primary home, then rent out the property’s primary home to full time tenants.

Denver Zoning Requirements

For the purposes of this article, we want to address some specific Denver Zoning requirements that you will need to consider for the potential addition of an ADU to your property. Following are key items to first check (and understand as you contemplate the possibility of an ADU building):

Zone Lot District
Lot Size
Lot Coverage

Zone Lot District

The very first thing to do is to look up your Zone District to find the assigned zoning for your property. A reliable online resource is: https://www.denvergov.org/property. Referencing this website you can identify your zone district. This should help you verify whether or not an ADU is a permitted building form.

Some of the districts that allow for an ADU structure are:

S-MU-3	E-SU-D1(x)	U-SU-A1	G-MU-3
S-MU-5	E-TU-B	U-SU-B1	G-RH-3
S-SU-F1	E-TU-C	U-SU-C1	G-RO-3

For an accurate review, please check the Denver Zoning Code, or contact ArcWest for assistance to determine the feasibility of an ADU addition to your specific property.

Lot Size

We have found in some rare instances that a property has the appropriate designation which permits the addition of an ADU structure, then review the minimum lot size requirements to find that the ADU is not permitted. For instance the minimum lot size in a U-TU-B district is 4,500 SF, and 5,500 SF in a U-SU-C1. These particular standards can be found under Denver Zoning Article 5, Division 5.3.

Lot Coverage

Now that we’ve confirmed the property lies in a district that permits ADUs, and the lot size of the property meets the standards, the next step is to review lot coverage. The zoning standards outline the maximum allowed coverage by both the primary structure and accessory structures such as a garage or ADU. There are a couple of details to calculating the total lot coverage that can make it a bit tricky. There are exceptions for front porches up to 400 SF, and the 50% exemption for the garage area provided the ADU is separated from the primary house by 15 ft or more.

Once you review and confirm these initial zoning standards, you very well may be in a position to design and build an ADU for your property. For the development of an ADU in the City and County of Denver, there are other requirements that must be considered as you continue to explore the feasibility of the ADU addition. These zoning standards will most likely apply: