Passive House buildings can be houses, offices, fire stations, apartment complexes or schools. They can be tiny houses or skyscrapers. Yep, Passive Houses are not actually houses, they also aren’t passive! It’s not the best name but it is part of a lineage so it stuck around.
Their construction can be anything, there are no required techniques or materials. It is not a checklist or points based system like LEED or our local Austin version AEGB but instead is a series of low energy and air tightness targets tha must be met.
To further complicate things there are two sibling certifications with different organizations behind them. Without getting too deep into the family feud, the US based group Passive House Institute US (PHIUS) split off when it introduced climate specific standards to the varied climates of North America, while German based Passive House Institute (PHI) kept the standard static regardless of climate. We are certifying Theresa as a pilot project under PHIUS 2018+, the latest iteration of the US climate based standard. For something with such noble goals and a tiny market share, splitting hairs (and resources) seems crazy to me but such is life.
To build our house to the standard we First had to design our building and vet it through PHIUS and the energy modeling software they use - WUFI Passive. That process told us - based on the size and shape of our house, overhangs, window size and location, efficiency of our HVAC and appliances, and the climate of Austin - how much insulation we needed and where, how good our windows needed to be and how air tight our building had to be. The whole thing is a process - if we added more windows we might have to beef up the insulation or make things more air tight, if we deeper overhangs to shade those windows we might be able to be less airtight. We had all of these little levers to pull on that helped or hurt us in getting to the energy use targets required by the certification.
Insulation is pretty obvious - you add more of it and you lose thermal energy at a slower rate (and thus save money and have a more comfortable space). A couple caveats here though. First, continuous insulation is more effective than insulation with thermal bridging - putting insulation between steel studs can reduce its effectiveness by up to more than half making potentially it less valuable than the cost of installing it. Second, adding more insulation thickness gives diminishing returns - inches 1-3 may give you twice as much value as the 3-6, which will give you twice as much value as 6-9. In NH, where I grew up, the amount of hours below 20 degrees is roughly the same as the hours above 100 degrees in Austin. BUT if we want to keep our homes around 70 degrees, that is a 30 degree difference in Austin and a 50 degree difference in NH. In colder climates those extra 6-9 inches may be worth a lot more than in hot climates.