How Does a Passive House Work?
IA Passive House is an integrated building system for the management of location, environmental factors, design, construction, materials, insulation, airtightness, thermal bridging, windows, shading, mechanical components, ventilation, humidity, lighting and appliances, renewable energy and other factors towards achieving the highest standard of energy efficiency. The Passive House Planning Package (PHPP), available for sale from the Passivhaus-Insitut, is the key design tool used when planning and building a Passive House.
It also serves as the basis of verification for the Passive House Standard.
Annual Heat Requirement:
Space heating or cooling demand of less than 4.75 k BTU / square foot / year [BTU = British Thermal Units]
Primary Energy Demand [total energy demand]:
Less than38 k BTU / Square Foot / Year
Airtight Building Shell:
Less than 0.6 air changes per hour at 50 Pascal [a Pascal is a unit of pressure] with a blower door test
Using the Passive House Planning Package (PHPP), energy balances can be calculated to an accuracy of
+/- 0.5 kWh [kWh = unit of energy equal to 1,000 watt-hours]. Originally based on European norms, the PHPP makes use of numerous tested and approved calculations to yield a building’s heating, cooling and primary energy demand, as well as its tendency to overheat in the warmer months. While the PHPP was developed specifically for Passive Houses, it is a design and modeling tool that may also be used for other types of buildings and projects, including retrofits of historical buildings.
The thermos bottle may serve as a useful analog for how a Passive House works. Regardless whether the contents of a stoppered thermos are cold or hot, because of the effectiveness of its insulation, heat transfer between the inside and outside is negligible and the interior of the bottle tends to retain a constant temperature. But the residents of a well insulated building need to breathe, and the higher the quality of the air the better. For this the Passive House depends on continuous ventilation.
Passive Houses employ Heat Recovery Ventilation (HRV) for dry conditions and Energy Recovery Ventilation (ERV) [heat and humidity recovery] systems to meet the need for good quality interior air where humid conditions are encountered. Energy/Heat recovery is a process of exchanging the energy contained in building air exhaust and using it to treat (precondition) the incoming outdoor air for Heating, Ventilation and Air Conditioning (HAVAC) systems as needed. During the warmer seasons, an ERV system pre-cools and dehumidifies while humidifying and pre-heating in the cooler seasons. The benefit of using energy recovery is its ability to meet ventilation & energy standards, while improving indoor air quality and substantially reducing HVAC equipment needs. For example, in the VOLKsHouse 1.0 project in Santa Fe at 7,000 feet with a dry, temperate climate, Heat Recovery Ventilation is employed and the heating and cooling requirements are met by a mini-split system about the size of a hair dryer.
Passive House also functions well in hot and humid climates. In such conditions, many of the same general components and passive strategies, optimized for local conditions, are employed. In areas where active cooling is necessary, the application of Passive House principles can dramatically reduce cooling needs. In more humid climates, ERV systems allow for the indoor environment to maintain a relative humidity in an appealing 40% to 50% range, under essentially all conditions. The only energy requirement for Passive House ventilation is the minimally low energy demand of the continually powered exchange system blower.
Principles of Passive House ventilation: moist, stale air is extracted from the kitchen and the bathrooms (extract air) while fresh air (supply air) flows into the living areas. As a result, the hallways are automatically ventilated. As a general rule, the ventilation system should be designed to provide 30 m3 [1 cubic meter = 1.308 cubic yards x 30 = 39.24 cubic yards] of fresh air per person per hour. For a living space of 30 m3 per person, this equates to a supply air volume of 1 m3/(m2h). The maximum temperature to which this supply air can be heated is limited to 50 degrees C [122 degrees Fahrenheit] to avoid odor problems resulting from burnt dust particles. The resulting maximum heating load amounts to 10 W/m [watts per minute], which can easily be met by the supply air. [International Passive House Association]
In some cases, a Ground-Coupled Heat Exchanger, sometimes referred to as an air well or earth tube, can capture heat from and/or dissipate heat to the ground using the earth’s near constant subterranean temperature to warm or to cool air. Earth tubes can be used effectively to pre-treat the intake air for Passive House ventilation.
Using Heat or Energy Recovery Ventilation and the principle of thermal conduction [the transfer of energy through microscopic diffusion], plus the automatic extraction of moisture through the system where needed, a Passive House provides an extremely comfortable home without draughts or cold corners, and enjoying a constant supply of fresh air. Further, fine filters are integrated into the ventilation system to keep dust, pollen, and other particulate materials out and to maintain an exceptionally healthy interior environment.
It’s a recurring myth that you can’t open windows in your Passive House. Please do.

Airtightness/Thermal Bridging
The performance of a Passive House is highly dependent on a superbly insulated envelope. The insulation of the structure must be continuous and completely airtight. There must be no thermal bridging or breaks in the insulation.
Airtightness controls the internal environment of a building. It is one of the most economical measures possible in achieving energy efficiency. Fortunately, it is relatively straightforward to construct buildings in an airtight way, although careful planning and good craftsmanship are essential. For each certified Passive House building, an airtightness air pressure test is carried out to ensure that the stringent Passive House airtightness requirements have been met. The airtightness Blower Door Test is performed to determine whether the total air leakage in the building meets the standard of less than 0.06 air changes per Hour @ 50 pa (Pascals [a unit of air pressure]) while under positive pressure and then again under negative pressure. This procedure often turns up problems to be corrected.
Building envelopes consist not only of “unbroken” construction elements like walls, roofs, and ceilings, but also include edges, corners, connections, and penetrations. Owing to breaks in the airtight insulation, energy can pass though these points much more easily than throughout the rest of the building envelope. Passive House stresses thermal bridge free construction whenever possible. The aim is to reduce thermal bridge effects to the point that leakage is so insignificant, it no longer needs to be accounted for in calculations.
It is often said that buildings or walls need to “breathe.” Actually, it may be more correct to say that assemblies need to be able to dry. The insulation of a Passive House is “vapor-open,” airtight but able to dry. Vapor-open insulation plus a highly efficient heat or energy recovery ventilation system are key to preventing moisture damage and mold growth.
Passive House insulation also provides an acoustic advantage –– even on a busy street, a comfortably quiet place to live.
High Performance Windows
Daylight and view are the two most fundamental attributes of a window. High performance windows must be clear and well positioned. They need to help reduce unwanted heat gain while still allowing light to enter a home. Insulated and insulating windows create warm interior glass surfaces and reduce frost, condensation and uncomfortable drafts. Energy efficient windows can substantially lower the costs associated with heating and cooling, help minimize peak loads and shrink the need for HVAC equipment.
As the weakest part of the building envelope, windows merit special attention in Passive House buildings. It is essential that the windows installed are of very high quality. Window frames play a particularly important role in insulation. Frames should not only be slim, they must be insulated; heat losses through conventional window frames are much higher than those through insulated ones. Significant thermal bridges can occur if a window is installed incorrectly in the wall. Windows in Passive Houses must be skillfully placed within the wall’s insulation layer to minimize thermal bridge effects. This generally includes extending the insulation so that it overlaps connections in the window frame. During warm periods in any climate, solar gains must be limited to keep the indoor environment comfortably cool. With large windows often forming an integral part of contemporary architecture, shading is crucial. In hot climates where heating is not needed, solar protective glazing effectively reduces solar heat load.
Triple Paned Windows:
Three layers of glass can deliver up to 50% greater energy savings than single-pane windows and up to 20% savings on top of double pane. While triple pane windows certainly provide the best energy performance, their biggest advantage is improved occupant comfort. Eliminating cold surfaces and generating very even temperatures throughout a room provide significantly higher comfort. The improved insulation of triple-pane windows also leads to other benefits like better soundproofing. The more layers the light waves and sound waves have to go through, the more insulated and quiet a home will be.
Low E-Coating:
Once the solar energy shining through a window is absorbed by surfaces inside a house ––
say by a tile floor or plaster wall –– the energy warms the surface which in turn begins radiating
its own energy. The energy radiated by the floor or wall is long-wavelength electro-magnetic
radiation. The suspended film with the low-e coating absorbs heat radiation (rather than
transmitting it), and greatly limits the re-radiation –– or emission –– of that energy. Thus the
term low-emissivity. In warm climates the absorbed heat is reflected outdoors, and in cold
climates the absorbed heat is reflected indoors.
Argon-Filled Windows:
Argon gas windows are a sealed units that are filled with argon between panes of glass to increase
energy efficiency. Argon is an inexpensive, safe, odorless gas that is used in residential windows to
prevent frost from occurring at the bottom of window and at the same time to increase sound-proofing
characteristics of the window. Combining low-e coatings with a low-conductance argon gas filling
boosts energy efficiency by nearly 100% over clear glass. Although gas will leak from the window over
time, studiessuggest that a 10% loss over the course of 20 years will only reduce the insulating value
of the unit by a few percent.
Renewable Energy Sources
While achieving energy efficiency is the foundation of the Passive House Standard –– in 2014 that standard was expanded to include renewable sources. “A building that produces more energy than it consumes is not only possible, it is often very sensible,” says Dr. Wolfgang Feist, Director of the Passive House Institute. The way in which this is calculated, however, is of critical importance when it comes to setting criteria for a standard. “A building that produces an energy surplus in summer doesn’t necessarily have a good energy balance. Photovoltaic systems typically yield very little energy in winter, which is exactly when the most energy for heating is used. Therefore, the calculation only works when the energy demand itself is also very low.”
Taking the example of a single family home, the new “Passive House Plus” label confirms that about as much energy is produced as is consumed, whereas the “Passive House Premium” seal denotes production of an energy surplus.
“The new classes view energy production in relation to the potential of the particular building in question,” emphasizes Dr. Benjamin Krick, senior scientist at the Passive House Institute. “A single family home built to the Passive House Standard can achieve an energy surplus relatively easily. Efficient buildings can do more with less, meaning that renewables placed on small surface areas suffice to affordably cover any remaining energy demand. For an apartment building it is much more difficult to fully meet primary energy demand, as such buildings have a far smaller roof area available per square meter of living space. It is for this reason that the new classes calculate energy production in relation to the ground area occupied by the building.” A future-oriented scenario in which only renewable energies are used throughout the electrical grid serves as reference for the evaluation. Passive House offers an attractive solution for the energy revolution while also serving as the basis for the “Nearly Zero Energy Building,” code which will be mandatory for all new builds throughout the European Union as of 2021.
If it costs less to construct and uses less energy,
why not live in a VOLKsHouse?