According to NABERS, the Australian building rating system, buildings worldwide “use 40 per cent of the world’s energy, emit 40 per cent of the world’s carbon footprint, and use 20 per cent of the world’s available drinking water.”
In addition, the U.S. Environmental Protection Agency says buildings are responsible for 30 per cent of raw materials used, and account for 30 per cent of the waste stream.
“Green” or “sustainable building” aims to improve those metrics through changes to material selection, siting, energy efficiency, waste reduction, and indoor air quality, while creating healthy and efficient structures.
Many builders and building owners have worked to make their structures greener, caulking air leaks, adding insulation, and upgrading HVAC equipment with more efficient units. Over the last two decades, the field of building science has played an increasingly important role in improving energy efficiency. Best practices are now tested and evaluated, and rating systems such as LEED and Green Star provide a checklist for new construction to adhere to.
Since LEED was created in 2000, more than 20,000 LEED for Homes projects have been certified. Green Star has certified more than 600 projects in Australia since its inception in 2003. And while both standards can demonstrate efficacy, both still carry the stigma that they increase costs beyond their value, making them appropriate only for high-end projects.
The Passive House standard, in contrast, is focused almost exclusively on minimizing each building’s energy use. It dispenses with the lengthy checklist in favor of standards for the building’s overall energy use, air leakage, and heating and cooling. It’s effective, cutting energy use by 80 to 90 per cent, but has also been labeled as overly expensive, and inflexible with design. Many Passive Houses are boxy modern designs.
Evidently, some builders are able to make the Passive House standard work with a traditional architectural design, at a cost comparable to more traditional and less energy-efficient building methods.
Adam Cohen runs Structures Design/Build in Roanoke, Virginia. One of his recent projects, a Craftsman-style home for Jason and Stephanie Specht of Thaxton, Virginia, has garnered considerable acclaim. The Specht home received the GreenBuilder Home of the Year Award for 2013 in the Best Mainstream Green category.
The Specht home, at 1800 square feet, with three bedrooms, two bathrooms, and attached garage, looks completely standard but is a certified Passive House and earned a HERS (Home Energy Rating System) score of 38. In comparison, a standard new home scores 100, and an Energy Star home scores 85 or lower.
Perhaps most surprisingly, the Specht home cost just $150 per square foot, thanks to extreme attention to detail and precise energy modeling software that almost exactly predicted the home’s annual energy use. Passive House certification, as mentioned, requires that a building meet strict standards for air leakage, energy for heating and cooling, and total energy use.
Meeting those standards has proven challenging for builders, but best practices include a super-insulated envelope, energy-recovery ventilation, high-performance windows and doors, and eliminating thermal bridging. Because Passive House buildings are so well insulated and air tight, heating and cooling systems can often be downsized for cost savings. In fact, some Passive Houses have even replaced the furnace altogether in favor of small, wall-mounted plate heaters totalling about 1500 watts.
Cohen’s approach makes use of all those elements while minimizing the use of non-standard materials. Some parts of the home are high end products, such as the imported windows and doors from Klearwall Industries, but Cohen says most of the house makes use of readily available components.
“What really is my secret sauce, it’s not the product, it’s the process,” Cohen said. “We take 100 per cent responsibility for everything, design, construction, commissioning, and monitoring.”
By designing and building the home, therefore, Cohen’s team can control more construction details to maximize performance and minimize costs.
At $150 per square foot, the Specht home compares favorably with a standard home. The National Association of Homebuilders 2013 survey results peg the average newly built US home at just under $400,000 and 2607 square feet.
In addition to building energy efficient homes and other buildings, he serves the Passive House Institute US as vice-chair of the technical committee, and trains other architects and builders in energy-efficient design and construction.