green home addition in arlington-rear elevation ALL PHOTOS BY KEN WYNER

Here are photos of a recently completed energy efficient remodeling and addition project in Arlington, Virginia.  The project earned a Silver Award in the county’s Green Home Choice program.

The project included a three story addition, as well as a remodeled kitchen, and other improvements to the existing house.  Features of the addition included careful air sealing, multiple layers of insulation, tripled glazed windows, and an energy recovery ventilation system (ERV).  The most prominent energy efficient feature is generous daylighting.

In terms of its design, a principle theme is flow.  The massing of the addition itself is rotated at an angle to the original house, to help relate it not only to interior spaces, but to the garden as well.   A serpentine path to the new portico, providing a diagonal approach, reinforces the theme.



The builder was Klockner and Co. of Takoma Park, MD.  Help yourself to a self guided tour:





This doorway was relocated to provide physical and visual access from the dining room to the garden.



As you enter the kitchen, the breakfast nook comes into view.



 Moving the door from the dining room provides a kitchen work space out of the traffic pattern.


 A detail of the walnut sink counter, by Treincarnation.


Family Room



View from the family room to the kitchen


Family room and desk


Desk, by Treincarnation



Approaching the master bedroom


Master bedroom


Master bathroom




Patio and sheltered entry way


The angled family room wing shelters the patio from the driveway and neighboring property


Soft color counterbalances the bold geometry


Last night, I enjoyed an intense conversation with my friend, Bill Updike.  Bill, who has been closely following the developing partnership between PHIUS and Building Science Corp,  is the green building specialist at the Washington, DC Department of the Environment.

We were talking about cost effective energy design, and Bill tossed off a comment that the key to any design–at least in our mixed-humid climate–should be the latent load of the building. When he said that, my mind lit up like a pinball machine showing three cherries.

Here’s why:  The latent load of a building–in effect, the amount of humidity inside your home that has to be removed for you to feel comfortable–is largely independent of how much insulation you use in the floor, walls, roof, and the qualities and disposition of the other components of the building envelope.  You can thicken your insulation as much as you want, but you will not substantially reduce the latent load.

So then, why not select the most efficient heat pump that will handle a given latent load, and then scale the envelope components to the point where that same heat pump can just handle the heating load during the winter months?

This is in contrast to Passive House methodology, where envelope and mechanical system design begins with the established value of 4.75 kBtu’s per square foot per year for specific heat demand.  Generally speaking, using the Passive House system, the insulation values are beefed up until the predicted annual heat load is no greater than that value. In theory, that is the point at which the ventilation system–in our climate, based on an ERV–is capable of distributing not only sufficient fresh air–but also the heated air required for thermal comfort. At that point, as the theory goes, a conventional heating system can be eliminated–in turn saving enough construction cost to pay for the extremely high levels of insulation and other envelope components that were necessary to hit the magic 4.75.

The fatal flaw of this system, however, is that even when the envelope is designed to achieve Passive House certification, the ventilation system may not be adequate to manage the latent load.  So a conventional mechanical system remains necessary–and the higher levels of insulation required for Passive House provide what can then be considered unjustifiably diminished returns.

So it seems reasonable to approach energy design from a individually determined performance standard–that is, latent load–instead of an arbitrary value, like the mystical 4.75 kBtu’s.  This provides a rational basis, that hopefully avoids the rapidly diminishing return for extreme levels of insulation.  Of extreme importance is that it may tend to offset the penalty that Passive House imposes on smaller houses, where the higher ratio of wall area to floor area exacerbates the diminishing return phenomenon. Conversely, none of this negates the value of PHPP or WUFI-Passive as design tools.

It was Deep Throat who said, “Follow the money.”  When it comes to designing energy efficient homes, it’s still good advice, to follow the money into the thickness of your walls, roof, and particularly your subslab insulation.  But I think the real story is to “Follow the water vapor.”  That is the key, in my book.  

So, thank you, Bill, for this epiphany. I’m eager to try this approach on the next project.  It may be that the results will not be too far off from a straight-up Passive House analysis. I’ll keep you posted…


passive house certification stampMy previous post, “A Post-Passive House Paradigm for Energy Efficient Design” was recently re-published in The Green Building Advisor.  This generated some lively follow-up; you can check them out here.

As it turns out in these dialogues, they lead you to reconsider your own assumptions, and things that you have been taught. Here are two notions I came away with from that experience:

This dialog brings to bear the nagging issue that underlies its topic–that is, the inherent fragility of what we build due to its vulnerability to moisture.

In my original blog post, I omitted the discussion that preceded the “epiphany.” What I said to Bill Updike that evening–spoken arguably in desperation–was that perhaps we are veering off into the weeds with our pursuit of these immaculate levels of airtightness and wall thickness, and that maybe the best approach for affordable, mass produced housing–a resource that is substantially denied to upcoming generations–maybe the best approach is some good prescriptive formulas based on regional climate, and most importantly, with a focus on vapor management.

Steve’s observation of the kid’s running in and out of the house all day reinforces that notion. And just imagine if the kids have a dog they need to coax along with them.

More fundamentally, we need to take a reality check on our own, personal requirements for thermal comfort. My mother grew up in an affordable mass produced home built at the brink of the Great Depression. The house included a state of the art device for mitigating latent loads during the swampy summers of Washington, DC: a sleeping porch. It would not provide ASHRAE levels of thermal comfort, but it damn sure was net zero.

You can see where this is going. Maybe the problem is not so much in calibrating the astonishing technology of ultra efficient minisplits, but in recalibrating our expectations, and our exaggerated sense of entitlement…


dropping back to illustrate my point that our expectations matter–for study purposes, I did some tweaking of my PHPP file for the Grant residence, changing the summertime overheating value to 80dF from 77, and the winter interior design temperature to 66dF from 68. I keep the T-stat in my own uninsulated home (it’s a high rise condo–I have no access to the wall cavities) set to 66, and I’m comfy with a fleece sweater on . In a modern house, with modest insulation in the walls, and low e- glazing, radiant heat loss is significantly defeated, further raising comfort levels.

The effect of these changes on the PHPP verification page is significant. Specific space heating went down to 3.95 kBtu(ft^2yr) from 4.73. Specific cooling demand was cut in half, to 1 kBtu(ft^2yr) down from 2.

Specific primary energy load (energy consumed at the generating station, and including line losses) went down to 33.8 kBtu(ft^2yr), down from 35.0. That is the equivalent of 610 kWh (or 226 kWh at the meter of the house)

looked at another way–it would have allowed the house to achieve PH certification with 2 1/2″ of subslab insulation, instead of 9″.

None of what is suggested here is a hardship. I think it is reasonable for PHIUS to consider giving people the option of defining their own comfort standard. We are all grownups, I presume.