The Passive House, or Passivhaus as it was originally named, is not a house but a concept through which buildings are designed to strict limits of energy consumption and air infiltration. (The old joke is that you can heat them with a hair dryer.) They are hugely popular in Europe but have had trouble gaining traction in North America. A few years back some of the American passive house consultants and designers split from the international Passive House Institute (PHI) and set up the Passive House Institute US (PHIUS) to address perceived problems in applying passive house standards in America. They claim that a system designed in northern Europe won't work in the United States where the climate is more extreme, with colder colds and hotter hots measured in Fahrenheit instead of Celsius. 

map of US by PHIUS

A snapshot from the PHIUS map, which helps homeowners can find the sweet spot for their area. (Graphic: PHIUS)

For the past three years, PHIUS has worked with the Building Science Corporation to develop a new standard that takes the differences in climate into account. The group's website explains the background:

The three-year study yielded a formula that has been used to generate cost-optimized performance targets for more than 1,000 locations. These metrics represent the "sweet spot" where aggressive carbon and energy reduction overlap with cost-effectiveness. PHIUS+ 2015 provides a cost-effective platform for attaining Net Zero and Net Positive buildings, and certified projects also earn U.S. DOE Zero Energy Ready status. 
In fact, they have pretty much thrown the whole Passive House dogma to the dogs, changing the air tightness requirements, the energy consumption limits and switching to climate-specific thresholds. There is some logic to all of this; sometimes the amount of insulation needed to meet Passive House standards in the colder states and in Canada border on ridiculous. However these changes are controversial, and the Passive House community in North America is divided into two camps, with many sticking with the original PHI system. 

PHIUS is formally announcing the new system on March 25 at the Bullitt Center (which MNN called the world's greenest office building) in Seattle, on the eve of the start of the Passive House Northwest Conference, which is studiously avoiding taking sides, but which I suspect will turn into a giant bunfight. I've been invited to deliver the keynote address on Thursday night, when I plan to avoid the issue and talk instead about smart homes vs dumb homes.

phi standards for houses

Soon to come in sugar-free too.(Photo: PHI)

Meanwhile the Passive House Institute has been busy too, taking a leaf from The Coca-Cola Company and introducing different flavors: Classic, Plus and Premium. When PHI started, solar panels were expensive and renewable energy was not on the group's radar. They preferred to reduce demand for energy instead of offsetting it with renewables. (This is one of the reasons that I think the Passive House concept has not caught on in America — people would rather add tech like a solar panel that increases supply than something invisible like insulation that reduces demand). As renewables dropped in cost there was growing interest in going net zero, and it has become a bandwagon that PHI couldn't (and shouldn't ignore.)  

But in fact, passive houses are perfect candidates for going net zero because they use so little energy in the first place, most of it going to making hot water and using electricity for lighting and appliances. Just going passive house reduces energy use by 90 percent; a few solar panels on the roof can take care of the remaining 10 percent. The new Passive House Plus. PHI explains:

 A building built to Passive House Plus is more efficient as it may not consume more than 45 kWh/(m²a) of renewable primary energy. It must also generate at least 60 kWh/(m²a) of energy in relation to the area covered by the building. In the case of Passive House Premium, the energy demand is limited to just 30 kWh/(m²a), with at least 120 kWh/(m²a) of energy being generated.
None of these changes touches the basic Passive House limit on energy consumption and heating demand; none of this climate-specific stuff for PHI; they remain resolutely universal, one standard for all. 

With its new standard, PHIUS is moving in a totally different direction from the idea of Passive House as it has been known; they are philosophically and practically different beasts, and should probably have different names. It should be an interesting conference; I suspect it might well be the last time they are both in the same room together. 

Related on MNN and TreeHugger:

Lloyd Alter ( @lloydalter ) writes about smart (and dumb) tech with a side of design and a dash of boomer angst.

Passive House changes: What flavor do you favor?
The Passive House Institute and the Passive House Institute US are making news this week as standards change and they diverge further.