It seems fair to say the Passivhaus standard will be a source of debate for the foreseeable future.
Many people like its simplicity. Some believe its one-standard-fits-all approach to performance isn’t practical. Some argue that Passivhaus criteria—the 0.6 ach at 50pa airtightness requirement, say, or the 15kWh per sq. meter per year heating and cooling limits—are arbitrary and, relative to their potential energy-saving benefits, unnecessarily expensive to meet in extremely cold climates.
Others say the criteria not only are worth meeting, but are actually reasonable starting points that can eventually be surpassed, in almost any climate, as building techniques and materials advance.
So in January, when Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Institute U.S. director Katrin Klingenberg blogged that the PHIUS Tech Committee would examine data from 100 PHIUS projects certified so far and would field comments from the building community about possibly relaxing the Passivhaus standard for some projects in extremely cold climates, responses to the idea were predictably vigorous.
Fine tuning, or unnecessary alternations?
Mike Eliason, a certified Passive House consultant at Brute Force Collaborative in the Seattle area, told Environmental Building News that relaxing the standard “is not really going in the direction that we need to be going. I feel like we should be aiming for a set level of consumption that’s even more conservative than most Passive House houses that are certified.”
In a recent GBA blog post on the subject, Eliason added that “relaxing the standard in extreme climates also seems to give blessing to maintaining the status quo instead of addressing the structural problems of said extremes. Maybe any single-family home, Passivhaeuser included, in isolated, über-cold climates can’t truly ever be sustainable.”
Marc Rosenbaum, cofounder of Energysmiths, responded to Klingenberg’s blog by pointing out that adapting cost-benefit models to Passivhaus certification might not be practical because we can’t know the future cost of energy, and that cost would vary significantly from region to region.
Many others seem energized by the possibility that cost optimization could in some way factor into Passivhaus criteria and that refining the criteria (more than one person suggested combing the heating-and-cooling-demand criteria) could yield positive results without weakening the standard.
The Tech Committee isn't expected to have a proposal ready for release until spring. The discussion, in any case, certainly won’t end if PHIUS does eventually modify its approach.