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Fall 2019 – Workshop #4: How to Construct an ADU

The fourth workshop for our fall season was led by Curtis Florence, a Development Manager at Clayco-CRG. It was during this session that we furthered our research around ADU design, construction and urban development. Curtis lead the discussion by asking the group, “If ADUs became legal, what would be the most economical way to build them? Instead of building an entirely new structure, what if the tenant purchased the ADU from a corporate vender?” Exploring the construction market, Curtis proposed examining two precedent assemblies. The first was an expanded prefab container house from Amazon, and the second was a wood storage shed kit from Home Depot. To jumpstart the conversation amongst participants, Curtis began by comparing the two small scale housing typologies.

The prefabricated home under review was a compact expandable container house. Three to five weeks after purchase, Amazon delivers the 800 sqft modular house to your doorstep. The light steel frame sandwich wall panels, doors, and windows of this compact structure makes this product easily transportable. No structural assembly is required, paired with the ease of preselected bathroom fixtures, kitchen appliances, interior finishes and solar collection. The cost of construction for the prefab house is front loaded into the fabrication cost - approximately $37,000 with an additional Amazon shipment fee of $1,000. However, additional costs could arise during the construction of the housing foundation or with the addition of a reinforced concrete pad. The excavation to connect an ADU’s utilities to any existing utility lines or city network would create additional fees for the prefab selection.

In contrast to the prefab house, the Home Depot shed kit requires less front-end costs. Starting at only $11,000, an individual buying the Home Depot product is provided with the materials and instructions to build the shell of their home. Once the shell is completed, the tenant has the option of personally selecting the quality and cost for all their own plumbing fixtures, interior finishes, kitchen appliances, etc. Curtis mentioned that once assembled the Home Depot product is not only cheaper to build, but larger in square footage. The new tenant receives a more spacious home for a reduced construction cost.

After Curtis’s presentation, the group began to carefully weigh and consider the two purchased assemblies. At the root of the debate both time and money continued to dictate the potential of construction viability. Curtis then offered insight by proposing to the group that it is important to breakdown the scale of a project. Reexamine a project with the following question in mind: How will time and money be impacted during each phase of a project? Consider thinking through the time and cost of each of the following phases: site clearing and excavation, setting foundation walls and footings, rough framing/structure, location of weather barrier, rough MEP locations and interior finish selections.

Towards the end of the session we applied the lessons we learned about the Amazon prefab home and Home Depot product to how we might build a new ADU in Chicago. We broke the group into three sections to run through different scenarios of ADU construction. Each section concentrated on generating a proposed construction schedule, cost assessment, consultant list, and breakdown of sustainable features. The first section focused on building an ADU over an existing garage. The second section designed an ADU based around the Home Depot product. The final section examined constructing an ADU as a basement renovation. At the end of the section breakouts, the group collectively concluded that building an ADU as a renovated space within the main house, whether as a basement unit or attic conversion, was the most ideal in terms of material costs, construction timeline and utilizing existing utilities.


ANNE BALL is an architectural designer and artist devoted to design that transcends scales, systems and environments. She approaches her work as a listener first, as a means to activate attentive solutions for people, communities and places.

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