The Passive House (PH) concept—slashing heating and cooling of buildings by up to 95% over a conventionally constructed home—represents one of today’s highest energy standards for homes.
The PH concept is a comprehensive approach to cost-effective, high-quality, sustainable construction. Two goals are targeted: minimize energy losses and maximize passive energy gains. Achieving these goals has led to extraordinary results—a PH uses up to 95% less energy for space heating and cooling than a conventionally constructed house.
What makes a PH so special? Mostly, its extreme attention to detail—using highly insulating materials, as well as high-performance glazing; eliminating thermal bridging; establishing an airtight envelope; and balancing heat/energy recovery ventilation. These strategies can keep a house warm passively—by using existing internal heat sources (people, lights, and appliances) and solar energy admitted by the windows. Even the fresh air supply can be warmed without mechanical intervention by using an earth tube—a passive geothermal heating-and-cooling system.
According to the Architecture 2030 campaign, an average, conventionally built, single-family home in the Midwest uses 14.5 kWh per square foot per year site energy for space conditioning, domestic hot water, and household electricity. A new home built to code has a site energy use of approximately 12 kWh per square foot per year. Homes built to Energy Star standards are about 20% more efficient, at 9.6 kWh per square foot per year. The PH design principles require that a building use no more than 1.39 kWh (4.75 kBtu) per square foot per year for heating and cooling, and that its total source (primary) energy for space conditioning, water heating, and electricity not exceed 11.15 kWh (38 kBtu) per square foot per year based on “treated floor area”—the discounted net-usable conditioned floor area. To achieve these energy savings, designers and builders work together to systematically implement seven principles: 1) superinsulate; 2) eliminate thermal bridges; 3) make it airtight; 4) specify ERVs or HRVs; 5) specify high-performance windows and doors; 6) optimize passive solar and internal heat gains; 7) evaluate and optimize energy gains and losses.
The insulation applied to a house slows heat transmission and helps maintain the contents at a relatively constant temperature. Warm contents stay warm and cool contents stay cool, even when the temperature on the outside hits the opposite extreme. In a PH, the entire envelope of the building—walls, roof, and floor or basement—is well-insulated. How well-insulated? That depends, of course, on the climate. To achieve the PH standard, the Tahan House, in Berkeley, California, required only 6 inches of blown-in cellulose insulation, while the Skyline House, in the far harsher climate of Duluth, Minnesota, needed 16 inches—almost three times as much. Often, the first feature of a PH to catch a visitor’s attention is the unusual thickness of the walls, needed to accommodate the insulation.
PH designers choose from a wide range of materials to create superinsulated buildings, including conventional lumber or masonry construction, double-stud construction, structural insulated panels (SIPs), insulated concrete forms (ICFs), truss joist I-beams (TJIs), or straw-bale construction. Similarly, designers can choose from different types of insulation including cellulose, high-density blown-in fiberglass, polystyrene, spray foam, and straw bale.
Green building goes beyond the energy factor. For example, spray foams have a high R-value and are easy to apply, but they are petroleum-based products and some of the foaming agents contribute significantly to global warming. Manufacturers are seeking to develop spray foams that do not have these disadvantages. Vacuum-insulated panels (VIPs) are a relatively new and pricey option with an exceptionally high R-value per inch. VIPs allow thinner walls, for situations when that is a consideration.
No matter which insulation is selected, it needs to be installed correctly. The application can be inspected and performance measured using thermographic imaging. All objects emit infrared radiation (IR), and the amount of radiation emitted increases with the temperature of the object. Thermographic cameras can measure heat loss, identifying areas where insulation is insufficient, incomplete, damaged, or settled. Thermal images of properly constructed PHs show little heat loss.