What is Passive House?
With a company goal of achieving net zero energy performance on all our projects, Passive House is the way we get there. Achieving Passive House performance requires a tremendous commitment to quality construction -- something we'll write more about in future blog posts.
The Passive House standard is a proven method for the design and construction of energy-efficient, quiet, comfortable, healthy and durable buildings. It is the only internationally recognized performance-based energy standard in construction and is often considered the most rigorous voluntary standard in the industry today. Buildings that are Passive House-certified consume roughly 90% less heating and cooling energy and 80% less total energy when compared to typical building stock. Because of this dramatic reduction in the energy consumption of Passive House buildings, achieving Passive House is the most straight-forward way to achieve net zero energy performance.
The Passive House standard prescribes an energy “budget” per square foot (or Energy Use Intensity), and a maximum amount of air leakage. How to meet the rigorous requirements of Passive House is up to the project team. The flexibility of the Passive House standard enables it to be applied to any construction type, anywhere in the world.
Here's a great video that explains how Passive House works:
The fundamentals of Passive House design are as follows:
• Proper Insulation: Passive Houses dramatically lower energy needs by increasing the insulation levels in the building to ensure conditioned air is not lost to the outside. This can be cost effectively-achieved in new construction by increasing the thickness of wall and roof assemblies. For example, a code-built wall for a new home in Maryland is R-19, while a Passive House requirement is significantly higher. For the Perry Street Townhomes our insulation levels are more than twice code requirements.
• No Air Leakages: A building’s air tightness measures the amount of indoor air that “leaks” outside. Air leakage reduces efficiency and creates what’s commonly known as a “drafty” house. Air tightness requirements under Maryland’s current Energy Code requires homes to lose or “exchange” its outdoor air no more than 3.0 times per hour (3.0 ACH). In other words, under the current building code the air in the average new Maryland home leaks out every 20 minutes. Passive House requires air leakage to be less than 0.6 ACH, five times more stringent than code.
• No Thermal Bridging: Thermal bridges are elements within a building’s envelope (walls, ceiling, and floor) where energy is easily transferred between the inside and outside of the building. For example, in the average new home’s walls where the 2x6 studs touch both the exterior sheathing and the interior drywall, the 2x6s act as a conduit, radiating out heat in the winter and coolth in the summer. In many Passive House walls, including those built by Flywheel Development, 2x4 studs are staggered on a 2x8 or 2x10 base plate, creating a thicker wall and eliminating thermal bridging from studs. In the thermal image above, the Passive House clearly stands out from the other row houses as the only one that appears “blue” because it is not radiating any heat.
• High-Performance Windows: Passive House projects typically use high-performance, triple-paned windows that are airtight and have no thermal bridges.
• Orientation and Shading: Passive House design utilizes shading and solar orientation to optimize energy performance. In the Northern Hemisphere, large windows are designed to face south, taking advantage of solar heat gain in winter months to “passively” warm the home’s interior and lower heating demand. In the summer, trees (or shading devices) are used to dramatically lower solar heat gain into these same windows. On Perry Street this goal was met by retaining the oak tree in front of the houses and planting new trees.
• Energy Recovery Ventilation: Due to the air tightness of Passive Houses, these houses rely on Energy Recovery Ventilators (ERVs) to mechanically exchange indoor air for fresh outdoor air. These are the same air handlers used in commercial buildings, just on a smaller scale. In traditional homes, air simply leaks in through gaps within a home’s envelope. By contrast, in Passive Houses, the ERV recovers the heat (or coolth) of the indoor air when exchanging indoor and outdoor air. For example, in winter months, the ERV’s heat exchanger uses warm exhaust air to warm cold outdoor air before the air is brought into the building’s interior. The reverse is true in the summer, when the indoor air is cooler than the outdoor air.