A Green Builder’s Dream Come True

At long last, plans for my first Passive House—a new home in Derwood, Maryland for Anne and Elliot Grant—are ready to submit for a building permit.  It is truly exciting to have clients who are committed to what is possibly the highest standard for sustainable design:  the Passive house standard.  Completing our Design Build team on this project is Joseph Klockner and Company of Takoma Park, Maryland.

Passive House Planning Package

The design includes preparation of the Passive House Planning Package (PHPP), an extensive energy modeling program that analyzes every important element of the house and its mechanical systems.  The program also considers characteristics of the site including micro-climate, tree cover, and exposure to wind.  Our PHPP was submitted to Passive House Institute United States (PHIUS) for pre-certification, and after some serious review and refinement, is nearly ready for approval.

Achieving Passive House Pre-Certification Requirements

To be granted pre-certification the completed passive house planning package must demonstrate a house that will use

  • a maximum energy for heating no greater than 4.75kBtus per square foot per year
  • a maximum total energy for all purposes no greater than 38kBtus per square foot per year.

To achieve these energy efficiency requirements, the house will be insulated to the following levels:

  • roof: R-69  (code minimum is R-49)
  • walls: R-54 (code minimum is R-20)
  • floor: R-37 (code minimum is R-19)
  • windows: triple glazed U-0.16 to U-0.21  (code minimum isU-0.35)

Further, the house must achieve an extremely high degree of air tightness.  During construction, the house will be inspected several times with particular emphasis on air tightness.  Passive House requirements permit no greater than 0.6 air changes per hour (ACH) measured at standard test pressure.  Conventional building code allows up to 3.0 ACH.  That would be five times higher than the Passive House value.

Using Natural Assets of the Site to Achieve Passive Standard

The lovely 3 acre wooded site is adjacent to Rock Creek Regional Park and Lake Frank.  The actual building location is in a small clearing, surrounded by tall tulip poplars and other hardwoods.  Although the dense tree cover will help keep the house cool in summer, it created a challenge in making the numbers work for the Passive House heating requirements.  Every window and door opening had to be individually analyzed to determine potential for net heat gain (or net loss) over the course of the season.  By trial and error, each opening was adjusted in size and glass type for higher or lower solar heat gain coefficients (SHGC) until optimum modeled performance was achieved.

Currently, International Energy Conservation Code prescribes a solar heat gain coefficient maximum of 0.40, to limit overheating in summer.  Passive Houses–no surprise here–must be in the 0.50 to 0.60 range.  The Grant Residence windows range from 0.53 on the east, north, and west, to 0.62 on the south.  To use code compliant windows would have a severely detrimental effect on the modeled performance.

NEXT POST:  Does a Passive House have to look weird?

For those who love decimal points, grid lines and spread sheets, please feel free to geek out on the statistical breakdown of our passive house planning package in the chart below.

passive house planning package chart by Abrams Design Build Passive House energy modeling figures for new green home in Maryland

The short answer is, no.

The “Tyranny” of Passive House

In his Discourses, Plato has Hippias The Sage assert that

“…law is the tyrant of mankind, and often compels us to do many things which are against nature.”

The Passive House system is truly rigorous.  Often it requires modifying a decision or restraining an impulse that would be natural in another context.  Specifying an open masonry fireplace in your design program would be a triple nightmare for the Passive House Consultant to deal with.

  1. The flue damper.  The darn thing would leak so much it would be nearly impossible to reach the air tightness level required to satisfy the energy models.
  2. The mass of the chimney would constitute a significant thermal bridge.
  3. Stoking up a blazing fire would probably very quickly overheat the super insulated space, forcing the occupants to open doors and windows.

Never fear.  The passive house occupant need not forfeit the vision of a cozy winter’s evening by the fire.  There are a few wood stoves and prefabricated fireplaces on the market that are virtually airtight.  They can maintain a fire at a low enough output to provide the cozy atmosphere that we naturally seek, without the disadvantages noted above.

The point is, that Passive House limits some decisions, but it does not dictate them.

Passive House Likes Traditional Home Styles

There are a number of architectural characteristics of a Passive House that facilitate performance.  To keep warm here in our Mid Atlantic winters, Passive Houses like to spread out in the sun, and look to the south.  At the same time, they like generous overhangs and shutters to avoid overheating in summer.  Provision for cross flow ventilation, such as windows on two exposures in each important room, and operable skylights, can reduce the need for mechanical air conditioning during the shoulder seasons.  In other words, it could easily look like a traditional bungalow or cottage.

Passive House also likes simple massing—corners, offsets, and projections present challenges to achieving airtightness, and inevitably introduce thermal bridges.  In this sense, it could also be a cape cod or colonial style house.

Some features fight against the grain.  Our clients, the Grants of Derwood Maryland, wanted mulled windows—but the muntin bars reduce the amount of light passing through by as much as 5%.  Passive House cares deeply about this—when this amenity was factored into the Passive House Performance Package (PHPP), the performance fell off perceptibly.

But there was always a solution somewhere, by enlarging south facing windows, or adding additional insulation to compensate for the loss of solar gain.

Are you wondering what this house is going to look like when it’s done?  Here’s a rendering of the Grant House.  Not too weird looking, is it?

rendering of custom built passive house by abrams design build in maryland

The Passive House cuts a strictly simple silhouette on the landscape.

SOME FOLLOW-UP on the “classic bungalow” project. It’s difficult enough to build a new Passive House–at least for someone (like me) who hasn’t built one yet –but to remodel an existing house to Passive House standards is, well, infernally difficult.  And to take a house in a historic district, where there are limitations to changes can one make to the exterior of the house–like wrapping the walls and roof with several inches of insulation and installing new cladding, or ripping out vintage double hung windows and replacing them with euro-style triple glazed windows–that pretty much stabs the idea in the back.  2L3V6411

Regardless, I wanted to see how the bungalow stacked up against the Passive House standards.  Without submitting the house to the full blown analysis, which might take 20-30 hours, I took a shortcut to determine what Passive House calls the Primary Energy Load.  The PE value includes all the fossil fuel based energy that comes into the house, including the gas line and the electric service lines.  As mentioned in the previous post, however, electrical energy is evaluated in terms of how much wattage was produced at the power station–of which, only about a third actually arrives at a typical home.  The other two thirds is lost to resistance in the lines and transmission equipment.

PASSIVE HOUSE ALLOWS an annual maximum of 38 kBtu’s per square foot of “treated floor area,” which is a German convention that takes the overall area of the house, and deducts or de-rates the portions of the area that are not usable–like walls, the underside of stairs, and such.  It works out to be somewhere around 70% of the overall area of the house, measured on each level.

So for the bungalow, the overall 2836 SF becomes 1985 SF of treated floor area.  Gas usage of 316 therms becomes 31,621 kBtu’s, and 33,236 kWh’s becomes 99,709 kBtu’s of generated electricity–for a sum of 131,330 kBtu’s for the year 2012.  That sum, divided by the treated floor area is 66kBtu’s/SF for the year–or about 74% greater than what Passive House permits.

This is not something to pat ourselves on the back over.  The original house, using this methodology, used over 80 kBtu’s/SF for the years 2007-2009.  The project is still a significant improvement, but in the context of reducing our impact on the environment, it is not a staggering achievement.

THE BOTTOM LINE IS–referring back to the previous post–how we live within our homes is as important–energy-wise–as how we build them.




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.

Getting back to the core question:  “Is sustainable affordable?”

The answer first requires a definition of sustainability—and offers an opportunity to distinguish sustainability from “Green.”  A sustainable method or material—or more importantly—a sustainable project, is one that can be produced in a way that does not significantly compromise other’s ability to produce the same thing in the future.  It looks forward to our offspring, not yet born.  “In every deliberation, we must consider the impact on the seventh generation… even if it requires having skin as thick as the bark of a pine.”[1]


A green method or material—or project—meets a set of standards.  It is flooring that comes from rapidly renewable sources, or wood from well managed forests, or a toilet that uses less water per flush.  It may be a Passive House project, which uses only so many Btu’s per square foot of floor area.  Each of these green attributes contributes to sustainability—but in itself, does not guarantee it.

So sustainability—as a working force—depends on a state of mind, as much as a checklist, or point system, or a certification.  Sustainable decisions and actions begin with objective considerations, but since our crystal balls are smudged and cloudy, our judgments must ultimately rely on intuition and faith.

From this point, sustainability must consider two things:  the resources that we take from the earth to create our built environment, and to maintain it—and the impact on the natural environment from these creations and activities.

[1] Attributed to the Great Law of the Iroquois


In my last post, I mentioned that sustainabililty is a mindset.

Ann Edminster, in a 2011 Green Building Advisor post “High Performance and Net Zero Homes” develops this concept, with revolutionary fervor, and no holds barred.


Ann Edminster, Green Building Advisor with a revolutionary mindset


Her thesis is that for the green builder, there is a hierarchy of tools for transforming how we design and build.

There is an ironic overtone to this passive house geek, in that Edminster places “mindset” at the top of the list, and energy modeling and technology at the bottom.


Ann Edminster graphic

Green Builder’s Change Toolkit






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…