What Is an ADU?

         Accessory Dwelling Unit is the term that planning and design professionals (urban planners, architects, engineers, etc.) use to describe a second, smaller house on a homeowner's residential lot. ADU's add value and financial stability to the property. The create a greater availability of small, affordable rentals for young adults or elderly residents with fixed incomes.

          Whether you're looking for a mother-in-law home or extra office space, Carriage Home Builders is here to guide you through the process from concept to completion. Our design process. We specialize in building ADUs that respond to your unique site and your aesthetic values. If you have any questions about putting and ADU on our property and would like to discuss the possibilities dont't hesitate to contact us.

                                                              (303) 618-1790


ADU Development overview

          Carriage Home Builders principles have over 70 years of experience. in the real estate industry. We understand that the process of building an Accessory Dwelling Unit can be confusing and stressful. ADUs, although small in size, represent a significant investment of time and money. Our goal is to make these projects as easy and painless as possible. 

        Our design process leads to ADUs that respond to your unique site, your aesthetic values, and the style of the main house. Each design meets the restrictions within the zoning codes and takes into account years  of creative experience to deliver a finished product  that our clients are proud of.


ADU Development Process

Second units provide homeowners many benefits when construction is complete, however getting to project completion requires multiple steps:

1. Initial meetings to determine ADU feasibility on your property.

2. Establish project budget and select ADU model.

3. Arrange financing

4. Sign Contract, submit deposit, and Carriage Home Builders will handle everything from design to delivery including:

          •  Engineering and warranties

          •  Zoning regulations, surveys and permitting

          • Order your ADU

          •  Site Prep (foundation and utility hook-ups)

          •  Oversee construction and delivery

          •  Set and stitch

          •  Complete servies contracted at purchase (landscaping, decks, etc.)


Zone Lot Depth Percentages

          The Zoning Code uses percentages of lot depth to define the front and rear areas of residential lots. These area definitions regulate height, setbacks, unit location, and bulk plane (explained below). The regulations for the Rear Lot typically are more limiting regarding height and bulk plane and usually have requirements regarding the use of alleys.


Second Unit Location


          There are requirements specific to ADU and tandem house building forms that determine where to locate a second unit. ADUs typically are located in the rear 35% of a lot. Also, lot orientation, ADU height, and amount of stories can affect where an ADU can be constructed to maximize outdoor light and views.


Building Coverage

               Building coverage is the ratio of structure footprint area (footprint). All structures include a primary house, garage, or an ADU. The % of building coverage is limited and varies by lot size and zone district. Refer to the zone district and building form of an existing house for specific building coverage maximums For example, in many zone districts the

footprint area of all structures may not exceed 37.5% of the zone lot area.


Side & Rear Setback

          Side and rear setbacks determine the required distance between the side and rear property lines and an allowed building. Generally, no part of a structure can be placed between the setback and property lines (in yellow, Figure F), however there are exceptions to setback requirements in the Design Standards division of each Zoning Code article (example: chimneys, overhangs, HVAC equipment, etc.)



           Height is how tall a second unit can be built. For ADUs and tandem houses, height can vary by zone district and location on a lot. For ADUs in many zone districts, height can affect where the structure is constructed for the purpose of maximizing sunlight

for surrounding property owners. If applicable, an ADU exceeding 17’ or one story in height must located the southern most setback line. Refer to your municipality's rules of measurement and the zone district’s ADU Building Form section for specific requirements.



           Generally, ADUs are limited to 1.5 stories but story requirements vary by zone district.

A half-story is a story that is limited in size (square footage). ADUs can be a 1-story unit or be built over a garage as a half or full story depending on its zone district. The number of stories may affect where the structure is constructed for the purpose of maximizing outdoor light and views.


Bulk Plane

          A Bulk Plane is the series of planes that form an invisible three-dimensional building envelope/volume on the property. Any new unit must be built within the bulk plane (see Figure K) and may limit a second unit’s height near the side setbacks. Bulk plane requirements will likely limit a building more than height requirements.


Bulk Vertical Plane Height

          This dimension defines how tall the side bulk plane can be. Specifically, it is the vertical distance measured from the side lot lines. This dimension influences the height of structures near the side setbacks. Bulk Plane Vertical Height varies based on Lot Depth Percentage.


Minimum Spacing between Units

           This is the amount of distance required between a primary house and a second unit. There are spacing requirements and building coverage exemptions for ADUs and primary houses. Building codes may also require specific spacing between units. This dimension is taken from the face of the second unit overhang to the face of primary house overhang



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