What is a Passive House?
Updated: Oct 24, 2019
Introduced nearly 30 years ago in Germany, Passive House has emerged as one of the most rigorous, yet simple, energy efficiency standards in the building world. As you may guess from the name, the primary idea behind Passive House is designing and constructing buildings that require minimal levels of energy to heat and cool. Differing from other efficiency standards with prescriptive-based platforms, PH is largely performance-based, requiring extensive calculations and testing. The result is a house that not only looks green on paper, but performs in the real world.
What are some of the key design attributes of a Passive House?
Site and building design to optimize sun and shading. Before complex mechanical systems, even ancient builders knew to harness the power of the sun. Today's reliance on these systems has led us to not only take this natural source for granted, but often design against it. Passive Home design starts with orienting buildings to optimize solar gain in the winter, and provide shading protection in the summer. The building axis, strategic room and window locations, window g-values, and exterior material selections are just a few of the considerations that factor into efficient PH design.
Super-insulation and air tightness. Insulation is key to stopping heat transfer through the thermal envelope of any building. With a Passive Home's super-insulation, a significant amount of the heating needs are actually provided by it's occupants, appliances, and an HRV - more on that below. The insulation doesn't just stop at walls, floor, and roof - windows can account for 50% of your home's heat loss; Passive Homes utilize highly efficient windows (think triple pane and thermally broken frames). Another critical piece pf this puzzle is the buildings air tightness. Passive Homes achieve exceptional air tightness, keeping conditioned air where you want it. High efficiency HRV's are then utilized to exhaust stale air while transferring it's heat to fresh intake air. This not only helps with the energy efficiency but provides excellent ventilation and air quality.
Eliminate thermal bridges. Thermal bridges are weak areas in the thermal envelope of a building that provide the path of least resistance for heat travel. Areas like corners, wall to roof, and wall to foundation connections can serve as 'thermal superhighways' for heat loss. While energy efficiency might be the first concern that comes to mind, the surface temperatures of materials in these areas can lead to the most damage. Cold and warm air meeting is a recipe for condensation, leading to potential mold issues and deterioration/rot of the building. Passive Houses use not only better details at windows, corners and connections points, but efficient design to eliminate unnecessary corners, cantilevers, etc. The result is a longer lasting, healthier building.
Above: (Left) Comparison of heat gains and losses, (Right) A thermographic image from the street of rowhouses - can you tell which was built to PH standard?
So what can you expect from a Passive House?
Energy certainty and operating savings you can take to the bank. Passive House performance mandates consuming 15 kWh/m-squared annually or less. Compared to typical construction standards, this can be roughly an 80-90% reduction in energy consumption. Consider how the marketing of cars has changed in the last decade - gas mileage is now a primary concern when shopping for a new vehicle, listed on all new cars. Passive House allows you to build and buy with the same confidence. No matter what the cost of energy may be, you'll know that you not only have ultra high performance home, but furthermore can budget and calculate your operating costs.
The most comfortable and healthy house you'll live in. Hand in hand with energy efficiency, high performance Passive Homes also deliver unparalleled comfort to occupants. Temperature stratification (vertical difference, think at head level vs. your feet), hot and cold spots (like near windows), drafts, and room to room temperature fluctuations in typical construction methods negatively affect comfort, mood and health. Passive standards are designed with strict guidelines limiting fluctuations and providing uniform temperatures. These healthy homes also provide excellent air quality, with highly efficient ventilation regulating carbon levels, and filtering air with a minimum of F7 filter.
Healthier buildings, budgets, and a minimized carbon footprint make Passive a great choice when considering green options. With significantly reduced operating costs, the additional cost to a mortgage is often flat, or with surprisingly low pay back periods. Another great feature of Passive House planning is that financial considerations are calculated, helping you to make a fully informed decision on whether or not it works for you.
Questions about PH, or how to go Passive with your project? Contact Elevate to learn more today.