UA News

It's one thing to build high-tech energy-and-water efficient homes. It's another to build them affordably for lower-income families.

The masonry block walls rose quickly on a Saturday morning as dozens of apprentices, high school students and University of Arizona architecture students studied the masons’ technique at a home site about a mile south of the UA campus.

This was to be the third water- and energy-efficient low-cost house built by the Drachman Design-Build Coalition, a nonprofit corporation formed by UA architecture faculty to introduce sustainable design to the Barrio San Antonio neighborhood of Tucson.

As saws droned in the background, Mary Hardin, an architecture professor, pointed out the first DDBC-built house, which went up beside the current work site. The second house in the series was built in back of the work site. A fourth house will go next door and a fifth will rise around the corner. Each has its own design that incorporates different sustainable building techniques and water-saving strategies.

“We were for years in the design-build studios building houses of alternative materials, one every year just to explore the use of alternative materials in this climate,” said Hardin.

They experimented with materials like straw bales and rammed earth that have high thermal mass. Then the city of Tucson approached them to build these sorts of model homes on five building lots in the neighborhood. 

“There are a lot of really high-tech ways to save energy and water, but lower-income people can’t get there,” Hardin said. The idea was to develop designs for efficient, modestly priced houses that could be duplicated around the city.

Step 1 was to identify workable strategies with architecture professor Nader Chalfoun and figure out how to keep them affordable.

“By the time we get through all of those we’ll know which of these strategies really work well and we’ll also have the utility bills and stuff from the families that are living in them,” Hardin said.

The first house, occupied by a family since January, has a hollow wall built out beyond the structure. “It’s a vented cavity,” Hardin explained as students cut lengths of steel siding with a table saw. Cool air is pulled in from below and warm air is vented above, cooling off the insulated wall behind it. “On the south side, you get a venturi effect where the air keeps moving,” she said. Sliding screens along the south side control sunlight exposure. Inside, sliding panels open two bedrooms to form one large room to maximize space.

The second house also uses super-insulation strategies to counter its placement, like a lot of Tucson houses, on a long, thin lot oriented east-west, the directions that are exposed to the most intense heat of the sun. The east and west walls are eight inches thick, filled with insulation and windowless. A courtyard brings light and ventilation into the house. “You’re not getting a lot of solar gain from the west and the east,” Hardin said.

The third house will employ a thermal mass strategy using an open-ended masonry block that is injected with insulating foam. “That will take advantage of winter solar gain and hold it inside the living parts of the house,” she said.

The city finds lower-income buyers for the houses. The donation of many building materials and the free labor of architecture students all help to keep the price down.

“We need to keep the mortgages at around $100,000,” Hardin said, “so we have to look for materials and strategies that will come in under that. We would have chosen to do the whole house out of insulated masonry, but it’s just a lot more expensive than framing. So instead we used the insulated masonry on the north and the south, which allows it – it’s got thermal mass.” They will place the windows on the north and south, so that in winter, the sun will heat the slab and the inside of the walls. “It adds to the heat gain in the house, and in the summer, we have overhangs so it can’t gain heat.”

Because of the lag from design to construction, students generally work on construction of a house designed by an earlier class, but will design details like shade overhangs. Then they will design the next year’s house.

Architecture undergrad Heidi Grimwood spent most of the morning moving block into place for the masons, cleaning grout after the walls went up and cutting lengths of steel siding. 

“You get a better idea about how things go together rather than looking at a book,” she said. On this day, she learned how electrical outlets are cut out of masonry.

“For our program, I think we focus more on sustainability,” Grimwood said. “In our designs, we’re always trying to incorporate sustainable elements, materials or building methods such as putting windows on the south facade instead of the east and west.”

Daniel Armenta and his wife, who is pregnant, moved into the second house in August.

A horticulturist with the Arizona-Sonora Desert Museum, Armenta is busy landscaping the yard, which benefits from three cisterns that collect water from the roof for irrigation. “The yard is also contoured to collect water and prevent it from running off,” he said.

“The house is built to deal with the desert heat mostly and sun,” he said. In addition to the measures to contain heat buildup on the east and west walls, he said, “We have deep windowsills to prevent the sun from going in when it’s at its highest angle.” The walls and ceiling are heavily insulated and the framework is built to minimize thermal bridging. 

The floors are concrete, he said, which retains the coolness of the night and prevents heat buildup. “That actually works really well, we’re finding.”

A Crowning Achievement in Green >