Passive House long ago broke out of the single-family house typology and has demonstrated its applicability to new construction at a huge variety of scales (from small schools to a 20+ story, glass office tower in Vienna) and typologies (from residential to commercial to institutional and everything in between.)  Still, since European communities consist of relatively high-density but not very tall buildings, every certified project that represents an increase in size or scope is greeted by Passive House enthusiasts with unconstrained glee.  Conversations can begin to feel like a game of one-upmanship.  10-stories in Belgium, you say? Pshaw- we’ve got a 50 unit project in Vienna.  Energy bill so low you don’t need a BMS? Whatever, our project doesn’t even have a heating system!  And so it goes, with each conversation revealing some new frontier entered, some old barrier surmounted. Though I had to spend lots of time nodding sagely as if I knew what everyone was talking about- it is clearly an exciting time to be a building science geek.  There remains, however, a frontier not entirely sorted by the Passive House crowd- and it is the one most pertinent to NYC: applying Passive House concepts to incremental retrofits.


Understanding the scale of the retrofit challenge, the European Union funded a program to develop a Passive House standard for retrofits- dubbed EuroPHit.  The language can get a little confusing, with EuroPHit the title of the whole program of research, demonstration projects and reporting, while the energy performance standard that will come out of it is called EnerPHit.  And the program has been been extensive, including a series of about a dozen demonstration projects around Europe, several years of research, and the collection of appropriate construction details.

The basic outcome of the program is a standard, EnerPHit, that provides two pathways to Passive House certification for the renovation of existing buildings; one based on a primary heating demand limit, and one based on the specification of Passive House certified components.   Those familiar with the Passive House standard will know one of it’s core performance metrics is a strict limit on the energy used to provide heating.  The EnerPHit standard simply raises that limit by 60%, acknowledging there are things existing buildings won’t be able to modify, like insulating their foundations, that are important elements of meeting the original PH standard.  60% sounds like a lot, but it’s important to note that this looser metric of roughly 7.6 kBTU/sf/yr is still a very difficult target. Similarly, the standard loosens airtightness standards by increasing the allowable air-changes-per-hour from 0.6 to 1.0.


In addition to the loosened primary heating demand requirement, EnerPHit also offers certification for projects that use all Passive House certified components throughout a building.  These include:

  • Building envelope insulation
  • Windows & doors
  • Ventilation (volume and electricity use)

Although the standards remain high, as they must to produce the most comfortable interior and ultra low energy use, these all seem like reasonable modifications to the original standard.  Meeting them will rely, as with the original standard, on an almost maniacal focus on the careful installation of high quality components.  There is a lot of education to be done amongst real estate sector decision makers (primarily building owners, who often do not have technical backgrounds), design professionals and trades people.  But one of the really important impacts of Passive House thinking is that it forces building owners, and everyone else involved, to acknowledge that money spent on things which do not ever require replacement (like insulation) or which only require refurbishment every 40-50 years (like windows) are a much better investment than mechanical equipment that will typically need refurbishment in less than 20 years, and whose performance significantly degrades over that period.


But what if you can’t really renovate all the components required by EnerPHit at one time?  This is the situation that almost every building owner finds themselves in, especially as we work our way down the food chain from highly capitalized real estate ownership firms in Class A office and market rate residential, to those with limited resources.  Most owners are not in a position to fully renovate their facades or windows or heating & cooling systems in a single project- and even if they had the funds would not even consider doing it while the building was occupied because of the disruption to the occupants.  This is an issue everywhere, but it is even more acute in NYC where our vacancy rate is incredibly low (and likely always will be.)  The EuroPHit team considered this carefully and later next month will outline a pathway for partial certification.  This will acknowledge that, say, just replacing your windows with Passive House certified versions is significant and owners that do so should receive an interim certification that allows them to market this commitment to potential tenants, investors and others.  Owners will need to submit a step-by-step plan to full EnerPHit certification over, say, 20 years, and will receive this partial certification when they’ve completed something like 20% of the full renovation measures.  In other words, you lay out your step-by-step plan to meet the looser EnerPHit criteria over time, and then demonstrate that you have completed measures that get you 20% of that energy performance goal.  For instance, replacing the roof insulation and the windows of one facade (but not yet insulating all the facades, or replacing all the windows.)  It’s a smart acknowledgement of the constraints felt by owners of existing buildings, as well as the fact that the marketing cycle of buildings is much faster than their life-cycle.

Mies told us, “God is in the details”, and if that’s true than the EuroPHit team has been in direct conversation with the almighty since about 2010.  We’re looking forward to the full rollout (in English!) of the EnerPHit standard and figuring out how we can apply their lessons here in NYC.

I’ll have more reflections on the conference in further blog posts later this week.

– Yetsuh Frank


  • Passive House / High Performance

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