More and more clients come to us at deZZign using words like "zero," "passive" or "active" house. Behind them is one wish: that the cost of running the house should approach zero. But these terms mean different things and come with different criteria, and not every "energy-efficient" home actually is one. This article is a plain-language glossary of energy efficiency: how consumption is measured, how a passive house differs from a net-zero one, and where these standards came from.
Construction isn't the final investment. It's followed by decades of heating, cooling and electricity bills, and over 20 to 30 years those costs often outweigh the difference in construction price. That's why it pays to understand the terms before design begins.
How a Home's Energy Efficiency Is Measured
The core metric is energy use per year per unit of floor area - in Europe, kWh per square meter. For a home you live in year-round, count the whole year, including summer cooling, which is growing even in mild climates.
Serious standards add two more measures. One is primary energy: how much energy "at the source" goes into heating, hot water, ventilation and appliances. The other is airtightness: how many times per hour air leaks through the envelope under a test pressure difference. Without airtightness, even thick insulation underperforms.
Energy-Efficient, Passive, Net-Zero: What's What
Based on these measures, homes fall into several categories. The lines between them aren't always sharp, but the logic is simple: from "uses less" to "produces more than it uses."
- Energy-efficient. A home that meets or beats the energy code where it's built. In Washington State, that code is among the strictest in the US.
- Low-energy. A home that uses several times less energy for heating than a typical one. There's no single international threshold, so it's worth asking how the claim was calculated.
- Passive House. The best-known standard, with clear criteria from the Passive House Institute: heating demand of no more than 15 kWh/m² per year (or a peak load of no more than 10 W/m²), very high airtightness and a cap on primary energy. In North America, PHIUS offers a climate-specific variant. More in our article What Is a Passivhaus?
- Nearly zero-energy (nZEB). A term from European law: a very efficient building whose small remaining demand is largely covered by renewables on site or nearby.
- Net-zero energy. Over a year, the home produces as much energy as it uses, usually with solar panels and a heat pump.
- Net-positive, or "active." Produces more than it uses, with the surplus exported to the grid.
Worth noting: when people say "energy-saving house," they usually mean a house that uses energy sensibly, not one that stores it. And a smart-home system is a control tool, not an efficiency class - it helps, but it can't replace good architecture and a good envelope.
Where the Passive House Standard Came From
The first passive house was built in 1990-1991 in the Kranichstein district of Darmstadt, Germany. It was a multi-family building that used less than 10 kWh/m² per year for heating, a fraction of what typical buildings of the time needed. In 1996, the concept's author, Professor Wolfgang Feist, founded the Passive House Institute in Darmstadt, which defined the standard's criteria.
A passive house places specific demands on windows, doors and wall assemblies. The core principles:
- Continuous insulation of the whole envelope, keeping heat in during winter and out during summer.
- High-performance windows: typically triple glazing in insulated frames, oriented to gain winter sun without summer overheating.
- Heat-recovery ventilation (HRV or ERV), supplying fresh air while recovering heat from the exhaust.
- Airtightness: no drafts and no uncontrolled losses.
- Thermal-bridge-free design, so temperatures stay even and cold corners don't collect condensation and mold.
A common myth: a passive house must have solar panels. In fact, the standard is about the house barely losing energy. Solar is a separate decision that turns a passive house into a net-zero or net-positive one.
