What is Passive House ?
- The passive house standard represents the highest level of energy efficiency and “green building”. - The passive house standard is where state and municipality energy codes are headed. - Public housing groups such as Habitat for Humanity and regional housing authorities and land trusts are starting to require new housing units to be built to the passive house standard as these groups tend to prioritize overall cost of ownership over initial cost of construction. - The roots of Passive House trace back to the 1970s, when the concepts of superinsulation and passive solar management techniques were developed in the United States and Canada. - More than 25,000 buildings have been built to the Passive House standard in Europe. The standard is especially common in multi-family housing where it often makes little financial sense not to build to this level of energy efficiency.
Concept “Maximize your gains, minimize your losses”. These are the basic tenets of the Passive House approach. A Passive House project maximizes the energy efficiency of the basic building components inherent in all buildings; roof, walls, windows, floors and the utility systems: electrical, plumbing & mechanical. By minimizing a building's energy losses, the mechanical system is not called to replenish the losses nearly as frequently. This saves resources, operational costs and global warming related pollution. Unlike any other structures, Passive House buildings maintain occupant comfort for more hours of the year without the need for mechanical temperature conditioning of the indoor air. The opposite has been the norm in this country where we have a history of inexpensive fuel and construction techniques with little consideration for energy losses through thermal bridging, air-infiltration, and inadequate levels of insulation.
Passive House is both a building energy performance standard and a set of design and construction principles used to achieve that standard. The Passive House standard is the most stringent building energy standard in the world The Passive House approach focuses on the following:
Strategic Design and Planning: Passive House projects are carefully modeled and evaluated for efficiency at the design stage. Certified Passive House Consultants are trained to use the Passive House Planning Package (PHPP), a tool that allows designers to test “what-if” scenarios before construction begins. They are also trained to use other software tools to identify and address potential thermal bridges and moisture issues at the design stage. Specific Climate, Siting and Sizing: Passive House design uses detailed, specific annual weather data in modeling a structure’s performance. Orientation of the windows can maximize or minimize solar gain and shading. Passive House theory leans towards minimizing the surface area to interior volume ratio, favoring an efficient shape to minimize energy losses. Super-Insulated, Air-Tight Envelope (But Diffusion Open): To keep the heating/cooling in, wall assemblies require greater insulation values to “stop the conditioned air” from leaving. Walls are typically much thicker than today’s standard construction. Passive House takes great care in designing, constructing and testing the envelope for an industry-leading control of air leakage. Blower door testing is a mandatory technique in assuring high performance. Walls are designed to be virtually air tight, while allowing water vapor to dry out. “If moisture gets into the wall, how does it dry out before damage can occur?” is a fundamental tenet of modern building science addressed in Passive House design. Wall assemblies are analyzed to allow for proper water and moisture management to make a long lasting and an exceptionally healthy building. Thermal Bridge-Free Detailing: Breaks in the insulation layer usually caused by structural elements and utility penetrations in the building envelope create a “thermal bridge,” allowing undesirable exterior temperatures to migrate to and “un-do” expensive interior conditioned air and creating colder interior surfaces that encourage the growth of mold. Passive House design attempts to minimize thermal bridges via progressive mindful architectural detailing. Advanced Windows and Doors: Historically these items are the weak link of a building’s envelope and thermal defense system. Passive House places significant emphasis on specifying high performance windows and doors to address concern. To meet the high performance needs of various climate zones, windows must meet strict performance standards regarding: component insulation, air tightness, installation and solar heat gain values. Energy Recovery Ventilation: The “lungs” of a Passive House come from a heat (or energy) recovery ventilator (HRV/ERV). It provides a constant supply of tempered, filtered fresh air 24/7 and saves money by recycling the indoor energy that is typically found in exhaust air. The heat from outgoing stale air is transferred to the unconditioned incoming fresh air, while it is being filtered. It provides a huge upgrade in indoor air quality and consistent comfort, especially for people sensitive to material off-gassing, allergies and other air-borne irritants. HRV's are fast becoming standard equipment in all new houses in Vermont. Heating: One of the best benefits to implementing Passive House design is the high performance shell and extremely low annual energy demand. This allows owners to save on operational costs as they can now significantly downsize a building’s mechanical system. Passive solar gains, plus heat from occupants and appliances supply most of the needed heat. Radiant floor, baseboard, or forced hot air heating systems are unnecessary! Alternative Energy: Considering alternative energy systems on your project? Building to meet the Passive House Standard is the smartest starting point. The significant reduction in energy use, allows alternative energy to power a greater percentage of a buildings demands. Likewise smaller demand equates to smaller and more affordable alternative energy systems providing higher cost-benefit value. Passive House design puts a project within reach for achieving true “Net Zero” performance (the building generates as much energy as it consumes over the course of a year), making use of alternative energy systems smaller thus more affordable and attainable.