The promise of Passive House is fairly well established.  From my perspective there is virtually no other standard that produces high quality, low energy buildings so reliably and cost effectively.  That it does so with a strict focus on interior comfort is critical.  Remember, the most “efficient” building is one with no doors, windows or occupants.  Passive House produces some of the most comfortable buildings in the world, and does so while solving the major riddle of efficient buildings: how to ensure reliable savings without spending too much money.  Implementing the standard in the US at scale represents some major challenges, but that is as it should be.  Things that are easy don’t usually have much impact.   My remaining thoughts from Leipzig:


The first challenge of Passive House is just getting the myriad stakeholders involved in buildings to think differently about them.  Actual building performance (as distinct from the anticipated performance our energy codes rely on) has been largely ignored for decades and, despite the market penetration of LEED and the major code improvements pushed forward by ASHRAE and ICC in recent years, changing this will take a concerted effort on all fronts.  On any given project there are a dozen or more stakeholders; from building owners, to property managers, facilities managers, equipment manufacturers and installers.  Each have methods that have become ingrained over decades and will be challenged dramatically by Passive House.  Some of our current processes are accidental, in place because nothing has challenged them for years.  Even these will be difficult to change, but at least logic will be on our side.  Other processes that might be in conflict with deep energy retrofits will be in place for very good reasons and our success will depend on the degree to which our industry can logically and capably address those concerns rather than expect them to get out of our way of their own accord.


Improving the performance of building exteriors is both critical and enormously challenging.  Because our codes take virtually no stance on air infiltration or thermal bridges, everyone from architects to engineers to manufacturers to contractors currently rely on details that produce buildings of very low quality.  What we consider “industry standard” is actually just the absolutely minimum we can get way without triggering a series of lawsuits.  One of the most common examples of this are “New York Lasagna” buildings- you know the ones, the many, many residential buildings that have exposed slab edges on every floor.  If your goal was a building with the most thermal bridges in the exterior they would look something like this- resulting in buildings that are uncomfortable (because of the cold spots on the floor), inefficient (because your heating and cooling is constantly fighting the heat loss of this thermal bridge), and frequently have moisture problems (due to the combination of thermal and air infiltration issues.)

Airtightness is another aspect of building science that has long been ignored by our codes but is directly engaged by the Passive House standard.  On one level, correcting leaky facades might seem as simple as sending an army into the building with caulk guns.  But doing airtightness right requires the air barrier be in placed in just the right position with regard to the insulation (a position that depends on the climate), and this requires that materials be constructed in a certain order, and with a certain care.  Needless to say, our current construction methods rarely consider these issues when the installation of materials are staged.  There’s no doubt our construction industry is up to the ask, but it will require significant education and not a little patience.  I would also argue for a steady ramp of new Passive House projects, to build trade capacity gradually, rather than a spike of new projects with everyone learning on the job at the same time.  The folks at Optiwin, one of the premier Passie House certified window manufacturers, estimated that there are 4000 PH certified designers in the US, but only 1,000 tradespeople.  When the market heats up we’ll need 10 tradespeople or more for every designer.

Airtightness and continuous insulation are labor intensive, and that’s a good thing.  As others have noted, you’re don’t send your house to China to have it insulated, and there is no airtightness aisle at Home Depot. Programs that fund or provide other incentives to insulate or tighten the envelope of buildings have a unique benefit, almost all the dollars stay within the community because most of the dollars are spent on people, not technology.  As the Mayor moves forward with his campaign to improve income inequality, it is worth noting that a significant amount of dollars spent on Passive House retrofits would go directly to the blue collar folks he aims to help.


While the envelope requirements and the limits to heating and cooling energy within Passive House are significant, the plug load energy limits might be even more difficult for our industry to absorb. Currently plug loads are totally unregulated in the US.  If you want to smelt aluminum in your office you just have to be ready to pay the energy bill.  But Passive House includes a strict cap on total primary energy use of 38 kBTU/sf/yr.  Instituting this in residential projects will be fairly simple, doing so in the commercial sector without a careful and gradual plan forward might lead to riots in midtown.


The cost of green buildings is one of the most hotly debated topics in the industry.  Despite study after study indicating that green buildings don’t have to cost more, that being green is a matter of priority and process rather than a reflection of the size of the budget- the perception still lingers that green is more expensive.  After all, if it didn’t cost more why wouldn’t everyone be doing it?  This sort of thinking misunderstands the role of inertia, which is probably the most powerful force in the universe, and the subconscious caution that pervades most decision making.  Both of these conspire, mostly silently but sometimes loudly, to keep things as they are.  The promise of Passive House is that it represents the nearest thing to a guarantee that you are spending your money wisely.  Certainly some Passive House components are more expensive than standard.  Triple pane windows with large thermal breaks, for instance, are going to be more expensive than a standard window without these features.  And, obviously, 12” of insulation costs more than 6”.  But fixating on these more expensive components ignores the whole point of the standard- you spend more on your envelope and a lot less on mechanical systems.

One of the most interesting case studies at Leipzig, presented by Nick Grant of Elemental Solutions, involved a series of schools in the UK which have demonstrated such low energy use that the next school in the series will not include a BMS system.  The math works something like this: the BMS costs $50,000 to install, and about $5,000 to service each year- but the school only uses about $1,500 in energy each year.  So how does the BMS “pay for itself”?  The more you learn about Passive House the more you find similar stories in which the “permanent” fixtures of a building (insulation, air barriers, windows) obviate the need for systems and technology that are often expensive, finicky and quickly obsolete.  As Lloyd Alter has put it, “A smart thermostat in a Passive House would be bored stupid.”

The financial performance of Passive House is not just about first costs and simple payback.  As a general rule, financial underwriters have not viewed energy efficiency as an asset value.  Meaning, your bank wouldn’t give you better loan terms because you have an efficient building.  Although banks do consider operating costs, savings from energy efficiency have varied so wildly that the financial underwriters couldn’t rely on them.  Passive House has the capacity to change all this.  The energy performance is so consistent that it might not be long before banks will favor projects that are certified.  This would have dramatic implications for individual projects, but also has the potential to significantly bolster the nascent market for “green” property investments, a long desired but slow to emerge transition.


Paradigms are not easy to shift.  But Passive House answers so many urgent questions in the built environment I have a hard time imagining it won’t have a huge role to play in the years ahead.  It promises to help us avoid disaster, but also dramatically improve our built environment for generations to come. Although the challenges of applying the Passive House standard to retrofits are considerable, the opportunity a successful program represents is far too great to ignore.  To reach the overall city target of an 80% reduction in carbon emissions by 2050, the Mayor’s office estimates the building sector has to reduce emissions by 60% over this period.  If that challenge is a mountain range, Passive House may represent the only passable road through the hills.  It may be a difficult road, full of heavy weather and dangers unknown, but we may have no choice but to make our way through it.


  • Passive House

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