Passive building is a set of design principles used to attain a quantifiable and rigorous level of energy efficiency within a specific quantifiable comfort level – or in other words maximizing gains, and minimizing losses. These principles can be applied to any type of structure, from single-family residences, to skyscrapers, to schools, to multi-family apartment buildings.
A Passive House standard window features a particularly high thermal insulation value. The heat transfer coefficient Uw has to comply with the European standards and be less than or equal to 0.8 W/m2K. Every window with an Uw-value less than or equal to 0.8 W/m2K is therefore a Passive House window and suitable for installation in Passive Houses, and is eligible for support through corresponding programs.
Passive House windows are not restricted to installation in Passive Houses only. Windows complying with the Passive House standard can be used in refurbishment projects for older buildings, as well as in a new building. These windows greatly enhance living comfort, and help reduce heating costs substantially, and therefore dramatically cut a building’s carbon footprint.
Passive House Advantages
- High level of coziness – no “pockets of cold air” developing in the proximity of the window
- No temperature swings caused by different temperature layers in the proximity of the window
- Inside surface temperature of Passive House windows do not drop below 17 degrees centigrade, even in winter
- As a result of the window’s efficient insulating properties it is no longer essential to install heating elements near the window area, allowing for additional design and furnishing freedom
- Extra costs for a Passive House are now minimal, and amortization is realized quickly due to extremely high energy cost savings
The outstanding thermal insulation properties of a Passive House window are first and foremost due to superior quality frame technology, in combination with triple glazing, and then the spacer installed for the edge seal. The windows also feature a high solar energy transmittance – the natural heat from the sun’s radiation can be utilized more effectively, and enhances the energy balance of the building. Beyond the comfort and draft-free environment the windows offer, they significantly reduce energy, thus creating substantial savings on heating and air conditioning costs.
Why Build With Passive House Principles?
- Protection for owners from future energy price increases
- Excellent return on investment (ROI)
- Reduced overall cost of ownership due to improved energy efficiency
- Reduced total net monthly cost of living
- Resale property value increases as demand for zero energy buildings (ZEB) grow
- ZEB building’s value increases exponentially compared to conventional buildings as energy costs increase
- Savings from avoiding expensive retrofits due to future restrictions, and carbon emission taxes/penalties
- Increased comfort from balanced interior temperatures (demonstrated with comparative isotherm maps)
Passive House principles are today’s highest energy standard, with the promise of slashing the heating energy consumption of buildings by a whopping 90%. Widespread application of Passive House designs equates to a dramatic impact on energy conservation. Data from the U.S. Energy Information Administration shows that buildings are responsible for 48% of greenhouse gas emissions annually, and 76% of all electricity generated by U.S. power plants goes to supply the Building Sector [Architecture2030]. It has been made abundantly clear that the building sector is a primary contributor of climate-changing pollutants. Passive House principles are the solution, as they meet building energy needs, and are affordable with an excellent ROI.
A movement toward the construction of highly efficient houses originated in the late 1980’s, when a rigorous energy standard for new buildings was established in Sweden. Then Swedish professor Bo Adamson and German physicist Wolfgang Feist designed a building system that exceeded this standard – the Passive House. The standard is based on research first started in North America in the 1970’s and 1980’s. The first prototype, a four-unit row house structure, was built in 1990 in Darmstadt, Germany. Since then, the Passive House movement has grown with more than 15,000 certified buildings in Europe, and 1,200 in the United States (since 2017).
The Passive House concept is a comprehensive approach to cost-effective, high quality, healthy, sustainable building, and the world’s most rigorous standard for energy-efficient construction. Heating and cooling related energy savings are up to 90% compared with typical building stock, and over 75% compared with average new builds. To gain Passive House certification, very exact quantifiable and rigorous levels of energy efficiency are measured, unlike some more vague green building standards.
Passive House Principles
- Employ continuous insulation throughout building’s entire envelope without any thermal bridging
- Create an extremely airtight building envelope to prevent infiltration of outside air, and loss of conditioned air
- Employ high-performance windows (typically triple-pane) and doors
- Use some form of balanced heat and moisture-recovery ventilation, and minimal space conditioning system
- Manage solar gain to exploit the sun’s energy for heating purposes during colder temperatures, and minimize overheating during the cooling season
Passive House Requirements
1. The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand.
In climates where active cooling is needed, the Space Cooling Energy Demand requirement roughly matches the heat demand requirements above, with an additional allowance for dehumidification.
2. The Renewable Renewable Primary Energy Demand (PER, according to PHI method), the total energy to be used for all domestic applications (heating, hot water and domestic electricity) must not exceed 60 kWh per square meter of treated floor area per year for Passive House Classic. .
3. In terms of Airtightness, a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50), as verified with an onsite pressure test (in both pressurized and depressurized states).
4. Thermal comfort must be met for all living areas during winter as well as in summer, with not more than 10 % of the hours in a given year over 25 °C. For a complete overview of general quality requirements (soft criteria) see Passipedia. [Passive House Institute 2017]
How to Build a Passive House Building
Choose High-Performance Windows and Doors.
Windows in a Passive House are designed, oriented, and installed to take advantage of the free passive solar energy that can be gained through them. Passive House windows and doors are extremely well built incorporating, tightness, thermal breaks, minimal air infiltration and exfiltration, all of which lead to extraordinary high R-values. The R-value is further enhanced by using low-emissivity (low-e) coatings on the window glazing. Low-e coatings are microscopically thin, transparent layers of metal or metallic oxide deposited on the surface of the glass. The coated side of the glass faces into the gap between the two panes of a double-glazed window. The gap is filled with low-conductivity argon or krypton gas rather than air, greatly reducing the window’s radiant heat transfer. The Passive House window eliminates any perceptible cold radiation or convective cold airflow, even in periods of extreme weather. Intus’ Passive House Certified windows are available in an array of options for any Northern America climate zone, and have been beautifully integrated into a variety of designs and building types.
In a Passive House, the entire envelope of the building is well insulated: walls, roof, and floor or basement. The climate zone dictates the level of insulation needed. To achieve the Passive House standard in Berkeley, California only 6 inches of blown-in cellulose insulation is required, while a home in Duluth, Minnesota, might need 16 inches – almost three times as much. Thicker walls are needed to accommodate the required level of insulation; Passive House designers have a wide range of different types of insulation to choose from: cellulose, high-density blown-in fiberglass, polystyrene, ozone-friendly spray foam, vacuum insulated panels (VIPs), and straw bale. No matter which type of insulation is used, Passive House builders must make sure that the product is installed correctly. Technicians using thermographic imaging as shown below, can directly measure the application and performance of insulation. These cameras can readily detect heat loss; therefore they can help identify areas where insulation is insufficient, incomplete, damaged, or settled.
Eliminate Thermal Bridges
Heat flows out of a building by the easiest available path – the path of least resistance. It will pass very quickly through an element that has a higher thermal conductivity than the surrounding material, forming what is known as a thermal bridge. Thermal bridges can significantly increase heat loss, which can create areas in or on the walls that are cooler than their surroundings (cold spots). When warm, moist air condenses on a cooler surface, moisture and mold problems can easily arise. In a Passive House, there are few or no thermal bridges, which means negligible heat loss and a less moldy and therefore healthy environment. Passive House designers and builders reduce or eliminate thermal bridges by limiting penetrations, and by using heat transfer-resistant materials. Thermal bridge details are analyzed during the design phase through thermographic imaging (as shown above), and can be used to determine the effectiveness of eliminating thermal bridges.
Create an Infiltration-Free, Air Tight Building
Airtight construction helps the performance of a building by reducing or eliminating drafts, whether hot or cold, by reducing the need for space conditioning. Air tightness also helps prevent warm, moist air from penetrating the structure, condensing inside the wall, and causing structural damage, as well as potential air quality damamge. Airtight construction is achieved by wrapping an intact, continuous layer of airtight materials around the entire building envelope. Insulation materials are generally not airtight – the materials used to create an intact airtight layer include various membranes: tapes, plasters, glues, shields, and gaskets. The air tightness of a house provides a measurable dimension of the quality of construction. Testing air tightness requires use of a blower door, which is essentially a large specialized fan. A technician uses the fan to assess how much air is infiltrating the building through all of its gaps and cracks. Specific leaks can be detected during the blower door test by employing tracer smoke, which allows any leaks to be readily detected and addressed. Passive Houses are extremely airtight and are built from timber, masonry, prefabricated elements, and steel framing members.
However, air tightness does not mean that you can’t open the windows! Passive Houses have fully operable windows, and most are designed to take full advantage of natural ventilation or stack effect to help maintain comfortable temperatures in the spring, fall, and even summer, depending on the local climate. Depending on the user’s habits and behaviors, windows can be opened without dramatic loss of energy.
Properly Ventilate by Specifying Energy or Heat Recovery Ventilation
Perhaps the most common misconception regarding Passive Houses concerns airflow. “A house needs to breathe,” builders might say disapprovingly. A Passive House does breath, and exceptionally well in fact! Rather than breathing unknown volumes of air through uncontrolled leaks, Passive Houses breathe controlled volumes of air by mechanical ventilation that acts as the “lung” of the building. Through the use of an energy recovery ventilator (ERV) or heat recovery ventilator (HRV) in cold, dry climates, the Passive House constantly seeps fresh outside air, and quietly exhausts stale inside air back outside the house. All this is done with very little energy loss and creates an exceptionally healthy indoor air quality. The ERV constantly exhausts odors and moisture from the kitchens and bathrooms at a very controlled rate, while the ERV simultaneously brings in fresh outside air and delivers it to the various rooms. The ERV runs 24 hours a day – 7 days a week, but it is still extremely energy efficient by moving small volumes of air at all times, and exchanging energy while allowing for air flow. It is important to note that the exhaust air from the bathrooms and kitchens are not mixed with the incoming air supplied to the bedrooms and other living areas. The two streams of air pass each other, exchange energy, but do not touch or mix, making the Passive House one of the healthiest building standards in the world.
Optimize Passive Solar and Internal Heat Gain
Passive Houses designers must minimize energy loss, while also carefully managing energy gains. This is why the first step in designing a Passive House is to consider how the orientation of the building will affect its energy losses and gains. Windows should be positioned to allow for maximum sunlight when sunlight is wanted, and minimal heat gain when heat gain is not wanted. The more direct natural lighting there is, the less energy will be needed to provide light. To increase the building’s enjoyment and efficiency, designers can orient bedrooms and living rooms to the south, and put utility rooms and closets where sunlight is not needed – to the north. However, it is not always possible to site a house in this ideal way. There may be buildings, trees, or landscapes that cast shadows during short winter days, blocking out much of the low sunlight. The designer may also need to accommodate the homeowners’ demand for a certain view that may not be view-able for an ideal orientation. Although, windows are designed, oriented, and installed to take advantage of the passive-solar energy that can be gained through them, the goal is not to simply allow for as much solar gain as possible. Some early super-insulated buildings suffered from overheating because not enough consideration was given to the amount of solar gain that the house would experience. The designer of the Passive House should balance and match solar gain within the home’s overall conditioning needs, and within the window budget.
In the Northern hemisphere, windows facing north allow for no direct solar gain, while those on the south allow for a great deal of it. In summertime, and in primarily cooler climates, it is very important to prevent solar heat gain. This can be accomplished by shading the windows. Roof eaves of the proper length can effectively shade south-facing windows when the sun is higher in the sky during summer, while still allowing for maximum solar gain in the winter when the sun is lower in the sky and the days are colder. Deciduous trees or vines on a trellis can also block out sunlight in the summer and admit it in the winter. In climates that have significant air conditioning needs, the designer will limit un-shaded east and west facing windows, and specify windows that have low solar gain, and low e-coatings. During the morning and late afternoon, low angled sunlight can generate a great deal of heat in such windows.
Another, perhaps less obvious source of heat gain is internal. Given the exceptionally low levels of heat loss in a Passive House, heat from internal sources can make quite a difference. Household appliances, electronic equipment, artificial lighting, candles, and people – all can have a significant effect on the heat gain in a Passive House. Passive House designers play an active role in what appliances and lighting systems are selected and they must take into account the heat gain from those sources when they calculate overall internal heat gain.
There are many elements of Passive House design that need to be integrated with one another. These include wall thickness, R-or U-values, thermal bridges, air tightness, ventilation sizing, windows, solar orientation, climate, and energy gains and losses. The PHPP is a powerful and accurate energy-modeling tool that helps a designer to integrate each of these elements into the design, so that the final design will meet the Passive House standard. The PHPP starts with the whole building as one zone of energy calculation. The designer inputs all of the basic characteristics of the house – orientation, size and location of windows, insulation levels, and so on. The PHPP can even be used to model such advanced features as solar water heating for combined space and water heating, or the contributions of natural ventilation for night time cooling. The PHPP then computes the energy balance of the design. If needed, the designer can change one or more elements – like the size or location of a window. Experienced Passive House designers often work with drawing programs and PHPP software simultaneously.
The developers of the Passive House concept mastered the integration of all these developments into a functional system to create a highly energy-efficient building. This concept can reduce heating energy consumption as much as 90% or more.
The number of inhabited Passive Houses in Europe today is in the tens of thousands, and popularity in America continues to grow. These buildings are not limited to homes. Schools, office buildings, health facilities, and large-scale housing projects have also been built to the Passive House Standard. These numbers, and the variety of designs, proves that the Passive Houses are not exotic research projects, but completely normal homes. Passive Homes are not full of complicated technology, but instead feature intuitive and simple devices, devices that any occupant can easily manage.
Contact us to learn how our Passive Certified windows and doors can be used in your next home, whether you decide to seek Passive House Certification or simply use a few of the design principles.
References & Excerpts
Passive House Institute US
Passive House Case Study
Passive Houses Directory
Homes for a Changing Climate
Excerpts from paper compiled by David Gano and Professor Laura Briggs
Passive Houses in the U.S. by Katrin Klingenberg, Mike Kernagis, and Mary James. ©2009 Aspen publishers