In the summer of 2023, Logan Havens and Gustavo Silva restored a historic adobe in Tucson’s Barrio Kroeger Lane neighborhood. They learned by doing, developing an understanding of the structure and its materials, and how to update the modest home to meet their needs. But before the couple even finished the remodel, they were already plotting their next project. When the City of Tucson introduced a competition for an ADU model plan library, Gustavo, a designer, and Logan, a photographer, developed a design that adapts the adobe vernacular of the Sonoran Desert. Then, at the rear of their plant-filled lot, they built an example where Logan’s niece, an undergraduate at the University of Arizona, is currently living.

To stay within their $100,000 budget, the couple aligned material, aesthetic, and labor considerations. Building with insulated concrete form (ICF) blocks that were plastered and coated with lime wash, for instance, eliminated the need for drywall and painting crews. Visible materials such as wood, construction hardware, and troweled concrete floors are part of the design intent. Kitchen and storage systems are from Ikea. And, not least important, significant sweat equity, along with a tight-knit network of fellow designers and skilled tradespeople, made their financial planning realistic.

The plan for the 650-square-foot, one-bedroom unit, dubbed the Detached Sonoran ADU, is now part of the City of Tucson’s ADU plan library. For those interested in building one, Logan and Gustavo have compiled a step-by-step guide to go with the plan set, which includes a contractor list that can help with a build out. (The couple estimates that with professional help, a unit can be built for around double what they spent.) Here’s how Logan and Gustavo built their ADU, and how you can build one, too.

Home Depot Special

Gustavo: When Tucson opened up a competition for a model plan library, Logan reached out to all of his architect friends, and he was like, “Someone design something good. We just need to have good designs here.”

Logan: They were all too busy. And so I was like, “Gustavo, would you do it with me?”

Gustavo: When we were designing the ADU, the code was more stringent than it is now, so our whole thing was that it had to be something Logan could build. We were pushing for nothing to be custom—everything had to be available at Home Depot, or somewhere, so anyone could build one. We also designed it to be built as is. You can change a couple of things, but there is no way of modeling the design beyond that.

Logan: The building is 38 feet wide, and the average lot size is 50 feet, so that would give you the five-foot setbacks required by the city on both sides for the average lot. We designed one side of the house for privacy, and kept the plan as narrow as possible to have more yard space between houses. The ADU has a traditional Sonoran-style three-sided parapet, and then ten feet is the highest we could make the ceiling without having an engineer. So everything is within existing code, including materials and allowances.

Material Honesty

Gustavo: I would say the ADU was pretty much designed in the style of the house; they both have the step-down parapet, which is something you see in our house.

Logan: And wood beam ceilings, heavy walls, lime plaster. Our house was a good model to replicate with conventional materials because it is kind of the oldest freestanding style of house in the city. So if you replicate it in historic districts, it will pass historic review. You want something to fit in, but you want it to look new. So, it’s a little taller, it’s a little sharper, it’s got differences. Nobody is going to think that they’re in an old house.

Gustavo always says, “Why does every American house look like anything but wood when it’s made out of wood?” So we thought that any wood-framed wall should show that it’s made of wood, or at least visibly not be pretending to be masonry or something else. For the roof, we could have done tongue-and-groove, but it’s half the price to buy pine plywood. We chose a metal roof because we wanted something that doesn’t take a lot of maintenance. It has a solar reflective index of 66, meaning it reflects enough light to count as a “cool” roof to better regulate indoor temperature in extreme heat; it also helps with the heat island effect, reducing the general ambient temperatures of a city. And it’s a non-painted surface, so it’s honest.

One of our challenges with the house was to choose materials that also serve as finishes. There are no secrets. We decided against drywall because we could have one stucco crew do lime plaster for the interior and exterior. With our ADU, we used two bags of sand, one bag of lime, a half shovel of white Portland cement, and your pigment. And so your total material costs are about a third of what you might otherwise spend.

One Plan for All

Gustavo: The plan can be mirrored or rotated. That way, you can orient it to what makes more sense for your house. With our property, we positioned it according to our house. We kept windows relatively small, so if you have south- or west-facing windows, you don’t have big panes of glass letting in sunlight.

Logan: We were never building it for a single site. We were building it to work within potentially any lot in the city, in every orientation. All the glazing is less than 10 percent of the wall mass, which means the building will be comfortable and use less energy, while still getting good light. The wall mass is R-28 insulation, which is two-and-a-half times higher than what is required by the existing code. When you look at the 1920s bungalows throughout the city, it was about air flow and light, and less about reducing heat gain.

Sticking to the Vision

Gustavo: By building the model, we’ve been able to easily convey the design to people. Some have called us and said, Oh, I like the ADU, but it has to be bigger, or it has to have higher ceilings. And Logan’s always like, come see the ADU, and then we’ll have a chat.

Logan: During the build process, I was like, Wouldn’t it be cool if we kind of did this, and it’s like, no, everything has to be exactly to plan, so that if somebody follows it, they will end up with exactly the same ADU as ours. So that was kind of the exercise. We had written into the plan set: Daltile Arctic White, four-by-four, lime plaster in this color, three Ikea PAX wardrobes or salvage or custom, or Ikea kitchen at this width. Everything was planned, with tolerances to allow for some mistakes.

And I think people’s perception of 650 square feet is that it’s going to feel small. But everybody who comes in ends up being quite surprised.

You Can Do This

Gustavo: I don’t think we would change anything. We could have done things differently, but we wanted to guarantee everyone will have the same result. The goal was to have something universal that could be replicated and that could pass historic review without having to be changed. So whoever comes after us, there is just more and more information. With each person who builds the ADU, hopefully it is just easier and easier, and they all keep informing each other.

Logan: We probably would have, like, concealed the air conditioning or done something like that. But that’s not practical when you’re sending it out into the world and claiming some level of affordability. Every customization makes it harder for any home builder or individual to build it, and will raise the price. We needed to make sure there was no oversight needed.

Gustavo: One of my proudest things is that the plan is very simple. It’s a five-sheet plan set. Each material is called out with finishes we would recommend.

Logan: The really nice thing about having built it is that nobody can say what we’re doing is impossible. I’ve done it—and I’m a novice.

The Adobe Revival Is Here

Project Credits:

Builder/Interior Design/Landscape: Silva + Havens

Also Appears In

Construction Diary: How a Tucson Couple Built a $100K ADU—and How You Can, Too