What Is Passive House Design
Passive House design is extremely powerful because it achieves so much by doing so little. The power of this approach comes from its stillness. There aren’t a lot of moving parts demanding energy consumption. So inhabitants enjoy year-round barefoot indoor comfort on a dime. In the 1970’s we referred to this type of house as “passive solar”. This would be a home designed and sited to make use of energy from the sun, natural wind currents and regional climate conditions. The 21st century Passive House is that and more.
The Passive House is built to maintain a near constant indoor temperature. It requires little or no assistance from heating, cooling and ventilation systems to offset seasonal temperature fluctuations. The small amount of energy it does require can be easily handled by renewable energy technologies.
What’s a Passive House Look Like
It can blend or it can stand out—your choice. Because the passive design standard takes a performance-based approach to energy efficiency, the house can look like any other house as long as it achieves the performance standard. That standard prescribes that a home will use less than one-tenth the energy allowed by the most efficient requirements set forth in the International Residential Code and Energy Star Programs.
The particular details of a given design program are adjusted to match the prevailing characteristics of a site and climate region.
How It Works
There are three requirements for a Passive House. The rules are simple and very strict. They focus on air infiltration, gas usage and electricity usage. If you dislike wonk-speak, skip the bullets below and go to the next paragraph. You may find it less irritating.
- Air Infiltration may be no greater than .6 air changes per hour (ACH) at 50 pascals (Note: International Residential Code allows 7 and Energy Star 6 air changes per hour)
- BTU Consumption for heating and cooling uses can be no greater than 4,755 BTU per sq. ft. (= 1.39 kwh per sq. ft.) annually (Note: International Residential Code average is higher by 10x and Energy Star by 8x)
- Total Energy Usage including appliances cannot exceed 11.1 kwh per sq. ft. – or 38039 BTU per square foot per year (Note: International Code allows 30-kilowatt hours per square foot and Energy Star 20 kwh/sf)
What’s Inside the Box
The PH is a comprehensive system. It employs high performance triple-glazed windows, super-insulation, and a nearly airtight building envelope to equalize temperature changes via radiation and convection. So, temperature variations from room to room would be minimal or non-existent. Building techniques applied to the structure prevent thermal bridging (temperature change via conduction). So, no more frigid floors or cold spots on exterior walls. Heat recovery systems capture and redirect internal heat gains from people and appliances. All of this, combined with mechanical ventilation, makes possible extraordinary reductions in energy use and carbon emissions.
High Performance = Low Cost
Again, the PH standard is based entirely on performance. If the house performs to standard, it is considered a Passive House. The intention is to achieve net zero energy usage. This challenges us to redefine how we think about our energy needs. We are saying that you can live in comfort while using little or no “produced” energy (renewable or otherwise). Obviously, this drastically lowers the operating costs of home ownership over time