Energy-Smart by Design
Building orientation, passive-solar design, and a radiant-barrier roof are key to energy efficiency in a hot-humid climate.
Synopsis: Controlling solar radiation and addressing infiltration of outside air are priorities when designing for a hot-humid climate. This contemporary home capitalizes on natural ventilation, with a radiant-barrier roof system that works efficiently in all climate zones.
This contemporary “farmhouse” is located in the booming urban hub of Central Austin, Texas. It belongs to an older couple whose objectives in having it built included downsizing from a much larger suburban home, reducing their carbon footprint, and living a more pedestrian-oriented lifestyle. To that end, they charged Barley & Pfeiffer Architecture with designing a comfortable, healthy, and resource-efficient house that would blend into the neighborhood of small-scale post-World War II homes.
Principals Peter Pfeiffer and Alan Barley have been designing high-performance homes in Texas’s hot-humid climate for over 30 years. Their projects commonly include metal roofing, deep overhangs, awnings, and other shading devices, as well as a combination of fiber-cement lap siding and locally sourced limestone veneer. Their intention is always to design energy-smart structures that rely most heavily on site orientation and passive-solar design and natural ventilation rather than HVAC systems. They also place great emphasis on good indoor-air quality. Peter’s ventilated radiant-barrier roof system is chief among their design strategies. It took 40 years to develop, and this house is the beneficiary of his decades-long research.
Two floors are better than one
The north-facing lot measures just 60 ft. wide by 96 ft. deep. To accommodate the desired volume of living space, they needed to build up rather than out, which has benefits in a hot climate. First, because roofs are a major source of solar gain, decreasing a roof’s size relative to the building’s volume reduces that gain. They advise clients to put the money saved by shrinking the roof surface into better building materials. Second, it minimizes the perimeter and interface between the wall system and the foundation slab, which is notoriously vulnerable to air infiltration—a major consideration when seeking to curb energy usage. “More house over less foundation is a more efficient house to build per square foot,” Peter says, adding that building up rather than out also means less impervious coverage, which helps with storm water management. Plus, a stacked, compact house with an air handler at the center supports shorter duct runs, which further reduces energy consumption by decreasing losses to friction along the ducts.
Cooler from the start
Energy demands can be mitigated right off the bat by correctly orienting the house on the lot. “A house should be inherently energy efficient without reliance on mechanical systems,” Peter notes. “You can get 10 times more out of your house by designing it to respond to the climate.”
This house is sited to be shut off to intense western sun and open to south-southeasterly breezes. To help capture those breezes, Alan says houses in this climate should try to incorporate screened porches and connected outdoor living areas. Come winter, the house shields those spaces from northwesterly winds, making them more comfortable. By adding fireplaces to screened porches, they can be used nearly year-round. The porch on this house not only takes in the prevailing breezes, it also works in sync with the stair tower, which acts as a passive-thermal siphon to draw warm, moist air up and out upper-floor windows. “Enhanced natural ventilation for homes in the south is becoming vogue again,” Peter says, “as people are becoming more and more aware of indoor-air-quality issues.”
Photos: Ryann Ford
From Fine Homebuilding #301
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- A Trombe Wall Solution for Passive-Solar Storage
- The Evolution of an Energy-Smart Roof
- Indoor-Air Quality and Ventilation for Homes in Hot-Humid Climates