Model Plan Library 

There is a specific substance, quality of light, and simplicity to Tucson’s historic buildings. It has always been a city with limited resources and a simple vernacular, and those limitations have created an honest and beautiful collection of buildings and neighborhoods.

Thick mass walls and exposed wooden ceilings defined early Tucson construction and have been applied to our ADU with current materials available within the city today. This house has been designed to fit into the majority of lots with varying levels of engagement or privacy with the existing residence. The house can be facing the existing residence to create a courtyard-style typology, the street on a corner lot facing the neighborhood, or creating a new life in alleyways. From the exterior, this house feels in place within the historic fabric of Tucson. In the interior, however, we have stripped the building down to the least steps and processes in a building and embraced quality standardized materials. The interior feels like the old and original Tucson, but in a new and contemporary way. In the 1800’s the available materials were mesquite beams, saguaro ribs, and adobe. Currently, the most available materials are Insulated Concrete Foam Blocks (ICF), dimensional fir lumber, pine plywood, and concrete. This design embraces the new materials, accepting them for what they are to create a fresh feeling of an old aesthetic: Heavy walls, solid floor, and wood ceiling.

Understanding sustainable architecture as responding to its natural environment, we designed the strategic placement of windows to maximize the quality of light but limit the sun exposure, a sloped roof to most easily collect the rainwater and route to ground basins, and an electrified house with the opportunity to run fully on solar. Our intention is a house built sustainably, made to last generations, and balancing a low impact during construction as well as through the lifespan of the structure.

We have tried and tested building in Tucson, and our ultimate affordability/quality/ease of building comes from self-building with Insulated Concrete Foam (ICF), specifically the locally produced ICF Blocks. We created a scalable plan with our ICF grid (everything on 1’x1’ dimensions) with the opportunity to expand modularly over time from a 460sqft studio to a 650sqft 1 bed/1bath to a 780sqft 2 bed/1 bath. This design offers flexibility and adaptability. Either the studio or the one-bedroom can be scaled up in the future. Framing doorways and cladding in insulation at points of future openings allows for a seamless building and an easy expansion as owners change family size, are able to save money, or have more equity in a home.

Our total design is based on what can most easily be built in part or in full by a homeowner. We would want the full process to be accessible and have chosen all processes to be as few and as easy as possible. However, a homeowner can subcontract any portion of the house or the full construction.

What is an ADU

A Casita, or Accessory Dwelling Unit (ADU), is a small, secondary home located on the same lot as an existing residence.

Since January 2022, Tucson has permitted ADUs in zones that allow residential uses. An ADU is generally tied to the existing house utilities like sewer, water, and electricity; however, it functions as an independent residence with its own address.

We generally see ADUs permitted to house elderly parents, expand livable space for smaller homes, and become income-generating rentals. 

How Much Do ADUs Cost?

The total cost can vary widely depending on how you approach the build, and we have multiple units built both as a DIY approach and as a full contractor build:

Plan Licensing: Studio / 1B 459 SF $2,500, 1 BD / 1 BA  646 SF $3,000

DIY/Owner-Builder Construction Costs: Around $100,000 + (depending on the amount of labor you do). We designed this unit to be self-buildable because one of the biggest ways to access affordability is to put in your own time or labor. To build, you sign an owner/builder affidavit that allows you to take on the build yourself. This will allow you to either work as a contractor to organize schedules and trades or to perform all or part of the labor.

-We personally built the unit to test the affordability, and our build was approximately $100,000. We hired a concrete crew, plumber, electrician, tiler, and plaster crew. The rest of the labor we put into the build.

Contractor Build Construction Costs: (no involvement): Typically between $185,000 and $230,000+. Estimates for our ADU with no modifications and no other work start at around $185,000, and people have chosen to add site walls, demo, and extra concrete pours for pads. All of the additional asks from a contractor will raise the price. The average pricing we are seeing is around $200,000.

What does a Detached Sonoran ADU include?

We’ve been designing and building in Tucson for nearly a decade and have put a great deal of thought into every aspect of this design. Our goal was to balance construction costs, long-term ownership costs, and efficient systems. 

While some elements may have higher upfront costs, we’ve carefully considered their long-term value. For example, a metal roof may cost around $2,000 more than a typical roll-on roof, but the difference pays off over time. Roll-on roofs often require recoating every 5-10 years under Tucson’s intense sun, whereas a metal roof can last 40-70 years with little to no maintenance.

That said, we were incredibly careful in balancing higher cost items with low cost and simple solutions to create an overall competitive cost ADU, while maintining a premium experience.

Insulated Concrete Form (ICF) Construction
Modern ICF construction — using foam insulation blocks filled with concrete — was developed in the 1970s and has since been used around the world. We chose this method because it offers several key advantages:

• ICF blocks are locally available and made in Arizona
  
• The blocks provide excellent insulation (standard insulation is R-13, while ICF is R-28) and lower energy costs in the long term. 
• The blocks are less vulnerable to pests, rot, or damage.
• The blocks are lightweight and easy to stack for DIY.
  

Cabinetry and Casework
We standardized the sizes of the kitchen and closet systems to allow easy choices of product like Ikea or reform, salvaged cabinets and closets, or custom fabricated casework. We wanted a guarantee that an easy product is available, while also allowing the space to customize or upgrade however you would like.

Metal Roof
We locally source a metal roofing system and recommend a Galvalume® finish, which meets Tucson’s Cool Roof Ordinance for accessory dwelling units (ADUs). The Galvalume finish provides a Solar Reflectance Index (SRI) of approximately 65, exceeding the city’s minimum requirement of 60. Compared to elastomeric-coated roofs, metal roofing offers superior long-term durability, often lasting 40 to 70 years with minimal maintenance. Additionally, the high SRI value reflects more solar radiation, helping reduce cooling loads and keeping the ADU comfortable during Tucson’s hot summers.

Quality Windows and Doors
We selected windows with either wood interiors and exteriors, or wood interiors with aluminum-clad exteriors. This allows us to balance historic preservation requirements where required, ease of maintenance, and cost-effectiveness. This, while maintaining a durable, beautiful, and repairable window system.

Plumbed for Graywater
We run all plumbing along one wet wall to consolidate water and venting into one area of the house. This allows two systems: blackwater (toilet and kitchen sink), and graywater (bathroom sink and shower). As both plumbing lines exit the house, a diverter valve allows water to be directed to an underwater percolation system that will water trees and landscape. 

Lime Plaster
We clad our ADU both inside and out with Lime Plaster. Lime plaster sequesters carbon, cleans air, and provides a durable finish. The finish of the plaster is determined by technique and can be smooth, sanded, dashed, or any other texture. 

Solar Ready
Our unit is designed with both electrical capacity for the addition of solar panels, but also an easy system for installing the solar panels on the ADU roof.