Passive House (Passivhaus) represents today’s highest energy standard for building performance with the promise of reducing the operational energy consumption of buildings by up to 75% in California, while providing superior comfort and extreme indoor air quality – all with minimal additional upfront investment. When coupled with renewable energy systems, such as solar PV, Passive House puts zero net energy within easy reach. Passive House is a proven standard, already applied to more than 100,000 buildings in all climate zones and is growing exponentially.
Benefits of Passive House
Passive House reliably delivers approximately a 90% reduction in heating and cooling demand and up to a 75% reduction in overall operational energy use when compared to conventional construction. The same protocols that deliver the extreme energy efficiency provide a more comfortable and healthier indoor environment — also addressing the climate crisis by dramatically reducing the operational carbon.
The benefits fall into five categories:
- Comfort – Constant desired temperature in all rooms, upstairs and down – no drafts, quiet, peace of mind, and tranquility;
- Healthy Indoor Air Quality – Continuous fresh and filtered air with up to a 95% reduction of airborne allergens and pollutants, including smoke and ash from wildfires;
- Energy Efficiency – The 90% and 75% reductions, mentioned above can dramatically lower bills and/or reduce the renewables required to reach zero net energy;
- Resilience – A Passive House building maintains the desired temperature much longer if power is lost – and doubles the impact of battery storage;
- Environmental Responsibility – Reducing energy demand from the built; environment is a major lever in reducing carbon and addressing the climate crisis.
Passive House Begins with Passive
A “passive” solution delivers desired performance naturally, as a function of design, and continues to deliver that performance, over time, with little or no intervention other than normal maintenance. Passive solar design orients a building to take advantage of what nature provides. For example: A building with windows on the south side, that allow the winter sun (lower in its arc) to shine through and warm the floor during the day, will require less energy to keep the building warm at night. The warm floor is acting as a heat source through the evening and into the night. An eave above those windows, positioned to block the sun in summer (much higher in its arc) from shining through and onto the floor, will prevent the solar heat gain and make it easier to keep the building cool during the days of summer. The siting and the eave are passive solutions and will reduce heating load in winter and cooling load in summer, naturally, and for as long as the building is in operation.
Many of the elements of Passive House design are indeed passive solutions. When you construct a building to be airtight, it stays airtight and maintains the desired temperature with a much smaller requirement for heating and/or air conditioning. Adequate and properly installed insulation reduces the loss of heat through conduction in winter and slows the intrusion of heat through conduction in the summer — and does so for the life of the building. Well-designed passive solutions work in the beginning and over time, and they do so naturally.
A Passive House is a very well insulated, virtually airtight building and a substantial portion of the heating is from passive solar gains and internal heat gains from occupants, cooking, bathing, appliances, etc. Add strategically located windows and skylights and you can provide appropriate daylighting, thereby reducing the need for artificial lighting. Employ LEDs and further reduce the already lowered energy demand.
Buildings don’t need to breathe. But occupants do, so a source of fresh air is required. A heat recovery ventilation system provides a continuous and balanced air exchange by exhausting stale inside air while bringing an equal amount of fresh air from outside. Both air streams flow through the heat exchanger but remain separate and do not mix. Since maintaining the airflow does require a minimal amount of energy, the air exchange is, at least partially, an active rather than a passive solution. Within the heat exchanger, heat from the outgoing air is transferred to the incoming air with up to 90% efficiency, so if it is 70 degrees inside and 40 degrees outside, the fresh air comes in at 66 degrees. The heat exchange process itself works naturally, is therefore passive, and requires only the human energy to change the filter periodically and perform occasional maintenance.
The natural order of sustainability is Passive — Active — Renewables. First, design to take advantage of all that nature and building science provide to lock in performance naturally. Second, add “right sized” active systems to provide fresh air, desired temperature, hot water, and resilience. Third, incorporate renewables to meet or exceed the dramatically reduced demand for energy. Ultimately, enjoy the comfort, healthy air quality, durability, and peace of mind that comes from your environmentally responsible choices in support of an all renewable, carbon free future.
The Five Principles of Passive House
Passive House performance is primarily achieved by optimizing the building envelope and incorporating the right, and right-sized, mechanical systems. Working together, they deliver the ideal combination of efficiency, comfort, health and resilience that will last for generations.
Optimizing the building envelope
- Air tightness: Eliminate, to the maximum extent possible, the unplanned leakage of indoor air that has been conditioned (warmed, cooled, filtered) for comfort and health — and at the same time prevent the unwanted infiltration of outside air that is too cold, too hot, and/or contains unwanted airborne pollutants, allergens, or moisture.
- Climate Specific Insulation: Once the air-leaks are eliminated, the primary way that heat escapes in winter or intrudes in summer, is conduction through the floor, roof and walls — strategic insulation of the envelope, based on expected temperature variations, can minimize this conduction, and as a result, reduce the energy needed for heating and/or air conditioning.
- Thermal Bridge Free Design: Any wood, metal, or concrete that spans through the envelope’s insulation from inside to outside will conduct far more heat than the insulation, and is called a thermal bridge — the envelope should be designed with as few thermal bridges as possible. Any thermal bridges that remain should be “broken” by inserting or adding a less conductive material somewhere along the conduction path.
- High Performance Windows and Doors: Occupants appreciate daylighting and views as well as the ability to come and go, so windows and doors are necessary components of the envelope. When closed they need to be airtight, free of thermal bridges, provide sufficient insulation value, and, depending on orientation, appropriate shading and solar heat gain properties.
Mechanical systems
- Continuous Ventilation with Heat Recovery: Continuous fresh and filtered air is provided by a balanced ventilation system — equal streams of outgoing and incoming air pass through a heat exchanger that transfers up to 90% of the warmth from the outgoing air to the incoming air. (The streams remain separate and do not commingle.)
(Note: Though not considered a Passive House Principle, depending on the climate, a small heating and/or cooling mechanical system may also be employed.)
Passive House is Flexible and Scalable
Many people think of a Passive House as a free-standing home, and it can be, but it can also be a multifamily building, a school, a hospital, a business, a supermarket — nearly any type of building. Regardless of building type, Passive House protocols will deliver the benefits described above.
A Passive House building can be designed and constructed with almost complete design flexibility. It can be modern, classical, historical, minimalist, contemporary, craftsman, and almost anything in between. Passive House performance is achievable with little or no aesthetic compromise.
Because of the health and environmental benefits of Passive House protocols, you will find Passive House structures from single family homes to multifamily buildings with hundreds of units, to a 26-story dormitory, and even an entire city block.
Evidence-Based Performance
A high-performance building incorporates countless products, systems, and controls that need to function in harmony in order to deliver expected performance. Many building standards are based on point accumulation, where points are awarded in different categories. Categories and the points available are based on the products, systems, and controls selected, the management of resources and/or waste, as well as various construction practices. This approach incorporates a broad range of positive products and/or practices and it generally delivers better performance. However, because it is prescriptive (do these things) rather than performance based, it is difficult to accurately predict and achieve specific levels of measured performance.
Passive House protocols and certification are based on actual performance and detailed modeling, rather than point accumulation. In simple terms, the three performance measures required are airtightness, energy required for heating/cooling, and total operational energy required. Airtightness can be measured part way through construction and again at completion. Detailed modeling using the Passive House Planning Package (PHPP) accurately predicts the actual performance of the completed building because PHPP incorporates the performance specifications of all products and systems to be utilized, climate, shading (based on building plans and natural shading on site), thermal bridge analysis, and myriad other factors. Rather than doing a lot of right things in the hope of getting the desired results, Passive House and PHPP provide “evidence-based performance” so you can know with confidence that the Passive House requirements for air tightness and energy usage will be met, and more importantly, that the building, large or small, will perform as expected from completion through decades of operation.
You can know in advance that your Passive House home, multifamily project, school, commercial or office building, etc. will deliver the efficiency, comfort, health and durability you are expecting. This is a primary reason that Passive House is growing exponentially and that all-electric, net zero Passive House design and construction is being recognized by cities across North America as the future of the built environment.
