The architectural portion of the plans for the new Passive House in Derwood, MD has been approved by the Montgomery County building authorities.   Site plan review is on going.

Concurrently, PHIUS‘s review of the project is nearly complete.   Ryan Abendroth and Lisa White have scrutinized nearly two dozen, densly detailed Excel worksheets that comprise the Passive House Planning Package (PHPP), and have identified several items that needed refinement.   Final revisions should be complete later today.

The long and short of the process is, our initial design was extremely close to meeting the Passive House Standards .  To make the nut, we will have to improve the thermal performance of the building envelope–so for simplicity and economy, we have chosen to add 1/2″ of insulation under the floor slab.

If you are ever suffering from insomnia, call me, and I will tell you all I learned about WUFI-Passive.  It is the blessing (or curse?) of geekdom that led me enroll in a three day long WUFI-Passive training class (sponsored by PHIUS—the Passive House Institute of the United States) in downtown Chicago last week.
passive house geeks

A room full of Passive House geeks — left brains are throbbing  PHOTOS BY DAVID RITTER

Don’t get me wrong—I love Chicago, and I got there a day early to wander the fabulous architectural canyons, and visit a few old friends at the Art Institute, like El Greco, Rodin, and Picasso.  And the class itself was conducted at the nexus of the universe of architecture, in the exquisite High Modern Equitable Building.  One can stand in its plaza at Michigan and Wacker Avenues, and from that single vantage point scan the history the skyscraper—from its inception in the days of Burnham, Jenney, and Sullivan, through its exuberant celebrations of the Wrigley and Tribune Buildings, to the megalomaniac culmination of the Trump Tower.  Fine art and architecture—and Passive House—the perfect concordance of right brain and left.

What is WUFI-Passive?  Simply put, it is the next generation of energy modeling, on track to supersede PHPP (the Passive House Planning Package), which only 3 years ago I had imagined was its apotheosis.  Previous posts tell more about Passive House, so I will leave it to the non-geeks to come up to speed here.  What WUFI-Passive adds to the mix is a comprehensive analysis of the behavior of water vapor as it passes through walls, ceilings, and floors, over a period of years, and modeling of the energy consumed in removing water vapor from a given space.  It then combines this information with another interface that includes all the inputs required for PHPP.  The result is a real-time, dynamic energy modeling system that factors in the full costs of dealing with cooling loads.  This is a marked improvement over PHPP, which could only summarize thermal loads by month or year, and dealt with latent loads in a cursory fashion.


This all goes to the heart of the split between PHIUS and its mother organization, the Passive House Institute.  As Passive Houses began to come on line in the United States, it became clear that PHPP—which was developed in the milder climates of Germany—was not ideally suited for the range of extreme climates here at home.  In class, it was noted that a recent Passive House project in New Orleans disappointed its planners—and occupants—because it failed to provide adequate comfort for its extremely humid climate.  It was telling to hear from Katrin Klingenberg, the founder and guiding light of PHIUS, question some of the fundamental propositions of Passive House.   WUFI-Passive will be the tool that gets us over that considerable hump.


WUFI-Passive—in its present state— is still a bit of a kluge.  Our instructor, Prudence Ferreira, who is likely to be the smartest-person-in-the-room wherever she goes, struggled with the idiosyncrasies of the program, and with class input, came up with a significant list of proposed refinements.  I stumbled through the fast paced class, often losing track of the lecture while I tried to correct some entry on our practice exercises.  Moreover, WUFI-Passive is an expensive piece of software, costing 460 Euros for a one year license.

For the near future, we can still use PHPP to certify our projects—but the future of Passive House is headed down WUFI lane.

After five rounds of revision, PHIUS has awarded the Grant Home project Passive House Pre-Certification status.  Youzza!  The reviewers delved into every detail of insulation, windows, and mechanical systems–even the amount of tree cover around the house site.

The easy part is over.  Now, all we have to do is build it.  Over to you, Joseph Klockner and crew…


Here are some piquant comments from John Straube, Ph.D., a professor of building science and principal of the Building Science Corporation. BSC is presently working with the Passive House Institute of the US (PHIUS) to develop energy performance standards and methodologies for residential buildings.

John Straube, Ph.D    John is among the top building scientists in North America.  His firm, Building Science Corporation, is the designer of the Net Zero Energy Test House, built on the campus of the US National Institute of Standards and Technology

John Straube, Ph.D     John is among the top building scientists in North America. His firm, Building Science Corporation, is the designer of the Net Zero Energy Test House, built on the campus of the US National Institute of Standards and Technology

The energy cost for a decent size IRC 2012 or EnergyStar v3 house is so modest, it is really hard to get any payback of almost any energy investment.  People buy $4 latte’s so they are hardly motivated by reducing the monthly energy bill from $120 to $100 by spending 10K on, say, good windows.  I have had a lot more success selling airtightness, windows, and insulation on the basis of improved comfort, health, disaster resilience, less dust indoors, and quiet, than I have had on direct payback.  Energy is cheap, and we are building new houses that are not expensive to run if you follow even modest energy standards.



Katrin Klingenberg (right) with a few of her students

Katrin Klingenberg, co-founder and executive director of the Passive House Institute of the US [PHIUS] is a visionary leader and inspiring teacher.  Since 2006, she and Mike Kernagis built the first Passive House in North America, established the Institute, and trained hundreds of professionals–myself included–in the Passive House system. During that period, at least 106 buildings have been built or precertified, using this system.

But it has become apparent that the Passive House system, developed in Germany in the 1980’s by Dr. Wolfgang Feist, did not translate seamlessly to  the wide range of N. American climates, and the actual performance of homes built in regions with extreme weather conditions failed to meet what had been modeled and certified prior to construction and occupancy.

Compounding the performance issue, the recent availability of cheap energy thwarted the rationale for the ponderous extra cost for thickened wall, roof, and floor assemblies, and other associated features. In some cases the pay-back for exceeding code standards is estimated to take a century.

So it is to her credit, and a testament of her courage and integrity, that Katrin and her associates are undertaking a serious reappraisal of Passive House methodologies and standards. What is most promising is PHIUS’s collaboration with Building Science Corporation, to develop a new set of climate specific, cost effective standards.

On the one hand, I can’t help but feeling a sense of disillusionment over what I had been taught. There is also the weird sense of validation, for the objections I encountered in studying–and implementing–the original methodologies. But that’s life on the bleeding edge–you bandage up your wounds and soldier on.

Read Katrin’s full report at: