Green Achievements

Historically, culturally responsive design reflected the local environment and climate. This was a natural occurrence in the days before the mass-produced housing development with no regard to solar access, prevailing winds, or other local, natural features. The Nageezi House design reflects both the local climate and culture. The building materials can withstand the harsh climate yet high winds, and require little maintenance. Materials and colors fit within the local context and include native stone pavers in the courtyard and wood beams from nearby forests. The reddish stucco tint echoes the reddish hue of the local soil.

Climatically and Culturally Responsive Design: The building design encourages passive heating and cooling and maximizes natural ventilation and daylighting.

Navajo homes or hooghans traditionally face east, to welcome the sunrise and to protect inhabitants from prevailing western winds. Here, the hooghan-inspired courtyard faces east, as does the main entry. This courtyard design provides cross-ventilation and daylight on two sides of all rooms. Thick, aerated concrete blocks on the building's exterior provide mass and insulation, modulating temperature and reducing the need for mechanical heating and cooling.

Minimal windows on the north and west faces assist passive cooling, while large windows maximize light from the southern exposure and heat capture in the winter. A well-insulated building envelope keeps indoor ambient temperatures stable. Radiant floor heating supplements the passive solar heating.

The building design encourages passive ventilation. Operable and motorized ventilation windows allow for an efficient and controlled air flow throughout the house. A thermostat regulates the clerestory windows to release hot air early on summer evenings and bring in nighttime cooling. A continuous trellis shades south-facing windows, reducing heat gains in the summer months. In the summer, brush also covers the trellis in the local tradition.

Locally Sourced Materials: One of the most interesting aspects of this project is its use of local materials, promoting local economic development and job creation. The design team is most proud of their use of Navajo FlexCrete in the building's interior and exterior concrete walls. FlexCrete is a building product that contains 60 percent reclaimed fly ash, a by-product of coal mining, instead of cement.

The Nageezi House was the first home ever to be built out of Navajo FlexCrete. The designers planned to use straw bale until they learned that the Navajo Nation had recently invested in a new plant that uses fly ash to make concrete blocks. After analyzing various materials, including straw bale, FlexCrete, structural insulated panels, and stick frame, they discovered that FlexCrete performed the best in this climate. The designers valued FlexCrete's combination of mass and significant R-value—as well as the fact that it is a locally sourced material that reuses a waste product while simultaneously supporting economic development on the reservation.

"Our challenge is to create modern homes that strive to come close to the extraordinary symbiosis of climate and culture that is inherent in indigenous dwellings."

Daniel Glenn

ASU Stardust Center

Given the particulars of this community, the designers viewed sustainability as an economic issue as well as an environmental one. The Navajo Housing Authority owns and operates the FlexCrete plant, and intends to use its product for housing on the reservation. The Housing Authority also hopes to use it to generate income for the tribe by selling it for use in homes in the greater area.

The Nageezi House also used other locally sourced and recycled products. Doors and windows came from demolished homes in the Phoenix area. The seven large juniper logs that make up the house and the native stone used to pave the hooghan courtyard were gathered locally. The roof's structure is comprised of local timber culled from Arizona forests via local fire prevention programs. Too small in diameter to use as conventional lumber, millers consider these timbers a waste material, and typically use them for compost. The designers used these 8-inch round timbers spaced on 4-foot centers, supporting a composite roof comprised of two layers of oriented strand board (OSB), with 5 inches of rigid insulation in between and metal roofing on top.



• Building oriented to take advantage of passive cooling and heating strategies and to protect it from prevailing winds


• Roof collects rainwater through inverted-shed design. Hand pump used to provide water for plants and animals

• Minimal landscaping uses traditional gravel skirt to transition from surrounding non-landscaped area


• Energy-10 and DOE II modeling

• Electricity use greatly decreased through daylighting strategies

Passive solar heating supplemented with radiant floor heating

• Passive cooling achieved with the use of natural cross-ventilation and night-time cooling of thermal mass

• 12-inch-thick aerated concrete exterior walls and 8-inch-thick interior walls provide both mass and insulation to reduce the need for heating and cooling (R-value of 35)

• Double-paned windows

• Reinforced concrete floors offer good thermal storage

• Rigid insulation roof with an insulation value of R-38

• All appliances are ENERGY STAR® rated

Materials and Resources

• Interior and exterior walls utilize aerated fly ash concrete walls (60% reclaimed fly ash content)

• "Waste timber" (from Arizona forests, too small to use for conventional lumber) used for roof framing

• Existing slab from previous home reused

• All reusable lumber from demolition utilized on-site or given away to locals

• During construction, cut blocks were stacked and reused whenever possible for the project, and all remaining blocks and cut blocks of usable size were retained on-site for use by the owner and their sons for future construction efforts

Health and Comfort

• Offgassing from paint was eliminated by using no interior paint. Exterior color comes from the stucco's integral colors, and interior concrete floors are stained

• Airflow maximized through use of operable windows; motorized, thermostat-controlled ventilation windows; and cross-ventilation design

• Solid aerated concrete block walls used to eliminate wall cavities where moisture can penetrate; each block is sealed from the outside with a water-based latex-base stucco to prevent moisture penetration

Durability and Ease of Maintenance

• Concrete walls and floors are durable and can easily be maintained at little cost

The builders reused materials wherever possible on this project, starting with the original house. Once dismantled, its usable lumber became the new home's decking and trellis, as well as the framing for doors and windows. The new house went up over the existing slab.

Energy Performance: Energy performance was simulated using both ENERGY-10 and eQUEST software. For a year after completion of the home, the designers monitored its actual performance around the clock, comparing it to a computer model containing the same characteristics via twenty "thermal couple sensors" placed throughout the house. Every thirty minutes, the sensors measured interior and exterior temperatures, heat flow through the walls, outside wind speeds, and solar radiation.

Energy performance during the first winter. Winter energy use performed close to the model's predictions. In January 2006, the Nageezi House used an average of 182,000 Btu/day, compared to nearly 400,000 Btu/day for heating a conventional home of the same size—a 52 percent reduction in a month that featured temperature lows of 4 degrees Fahrenheit.

Initially, the designers predicted that heat loss during the night would trigger the need for the radiant heating sys-

The home's roof design collects rainwater through inverted shed design, and it is then stored in a buried water tank.

© ASU Stardust Center for Affordable Homes and the Family.

tem to heat the house during the morning. However, it turned out that the thermal mass of the concrete floor played a role in keeping the indoor temperature stable throughout the night, retaining enough energy to continue to passively heat the house for over five hours in the early morning. Then, throughout the day, the glazing on the south façade brought in enough warmth that passive heating alone kept indoor temperatures within the thermal comfort zone. According to eQUEST, passive heating reduced overall mechanical heating by 15 to 20 percent. Reduced gas consumption for space heating saves the residents nearly 50 percent, or $3.50 daily compared with conventional homes.

Energy performance during the first summer. Computer simulations forecast zero cooling need, thanks to the concrete block's mass, as well as nighttime flushing through the automatic thermostat-controlled ventilation windows. On the hottest day of the summer (which reached 96 degrees F), the air temperature inside the home rose two degrees beyond the recommended thermal comfort zone for four and a half hours, reaching 85 degrees F. (ASHRAE

55, the adaptive thermal comfort model calculation, recommended a maximum indoor temperature of 82.76 degrees F.) On the coolest day of the same month, the outdoor temperature dropped to 54 degrees F. However, energy stored in the house's thermal mass helped to maintain a comfortable temperature of 76 degrees F. During this month, the passive solar design of the home kept temperatures within the comfort zone for over 90 percent of the time.

Based on feedback provided by the monitoring, the design team has been able to observe how behavioral changes affect energy performance. For example, they observed that the number of days the house remains within the ASHRAE 55 comfort zone parameters in the summer improves when the homeowners keep their windows open longer during the night.

As of August 2006, the home used 70 percent less electricity than a conventional home—even less than predicted. For example, in July 2006, the model predicted the house would use 1.10 kWh/month, yet it only used 0.601 kWh/month. Gas use was nominal—for cooking and water heating only—and the residents used no gas at all for heating between April and October. It is worth noting that the Navajo couple living here uses fewer resources than their average American counterpart.

0 0

Post a comment